R100 hard roll on surging

[jforgo]

On my 82RS, I am having a surge/sputter when I roll on hard.
Valves are adjusted.
Plugs have correct gap.
Idles beautifully.
Thought it might be diaphragms, so I just replaced those.
Bike came with too small main jets - went back to spec 160.
Needle was too high, reset to 2d position per spec.
New air cleaner.
Air injection system is gone.
Air tube connections are tight.
In line and in petcock filters clean.
Under tank trigger unit cleaned, heat sink coating renewed, connections cleaned
If I slowly run throttle up, then bike runs fine continuous for several minutes @ 6800 - so I do not suspect ignition can - or fuel flow.
No visible arcing under tank at night.
Surge/sputter persists.

ideas, o wise ones?

[tghsmith]

water in float bowls, float level to low, timing unit not advancing?

[fracture]

You state that when you roll on hard (I assume you mean you open the throttle rather quickly) there is a sputter/surge. Does this sputter continue for a short time (maybe a second or two) and then the engine runs normally, or does the sputter continue indefinitely as long as the throttle is held open?

[GeorgeRyals]

Sometime marginal condition plug wires/caps or coils will do that under load like acellerating hard. It's usually worse if you are a gear lower than you should be. If you acellerate smoothly/slowly they don't do it.

[jforgo]

You state that when you roll on hard (I assume you mean you open the throttle rather quickly) there is a sputter/surge. Does this sputter continue for a short time (maybe a second or two) and then the engine runs normally, or does the sputter continue indefinitely as long as the throttle is held open?

As long as it is cranked hard, near or full throttle, the sputter/occasional surge persists.
Yet if i take it up there slow, ran fine continuous high RPM. But roll off, then back on, forget it

[shire2000]

Last summer had a very similar problem with my Brother-in-law's Girlfriends new to her 1978 R100. Pulled the carbs apart and replaced all the O-rings and other little rubber bits, reset the floats and all was well. Runs smooth as glass and pulls hard from stop till I chicken out. Way more power than she will ever use.

So 2 main things come to mind.

1st. Check those floats and ensure they are adjusted just right. If too low, then you will get to much fuel dumped in all at once, which will cause sputtering, etc.

2nd. Check all the little rubber bits in the carbs. All the O-rings, etc. All it takes is a very small imperfection and it can cause no end of headaches. For what they are worth, I replace them pretty regularly, about every 2 years, just to be on the safe side. This is especially true if bike sits for any length of time, like over the winter.

One other thing, from what RPM are you doing the hard acceleration? Anything below 2500RPM and you should expect it to stumble and stutter - We used to call it Bogging down. Basically the engine may not be turning over fast enough to accept all that extra fuel and will stumble until it can get to a high enough RPM to be able to accept it. These bikes do like their revs.

On my R100RT, if I have the revs below 2500RPM and need to accelerate quickly, I always punch it down a gear to get into the power band. Usually likes to cruise at 3000 or above.

[fracture]

OK, the additional information may be a clue.

More questions, I want to be sure I understand the symptoms:

Let's say you are cruising along on the freeway and suddenly whack open the throttle. You get a stumble, correct? And the stumble persists as long as you are holding the throttle wide open, correct? If you back off the throttle while the stumble is happening, does the engine return to normal operation?

[jforgo]

OK, the additional information may be a clue.

More questions, I want to be sure I understand the symptoms:

Let's say you are cruising along on the freeway and suddenly whack open the throttle. You get a stumble, correct? And the stumble persists as long as you are holding the throttle wide open, correct? If you back off the throttle while the stumble is happening, does the engine return to normal operation?

Whacking it open does cause the stumble, sometimes surge then tumble. And yes, if I back off it will smooth out

[fracture]

jforgo:

I do not claim to be a carburetor expert, but I think you are running rich at throttle settings near or at wide open.

When you whack open the throttle, the slide/diaphragm is pulling the needle completely out of the needle jet. The main jet is now doing the fuel metering. When you back off the throttle, the needle drops, thus closing off some of the needle jet area. Mixture is now back to normal.

I suspect the reason it runs normally when you "sneak up" on full throttle is that the needle is never completely pulled out of the needle jet.

You said you put in a 160 main jet. That sounds right for a bike of that vintage, assuming everything else is per factory spec. However, additional fuel is getting in. Maybe thru the choke, thru a leaking O ring in another circuit, etc.

If you have a smaller main jet, maybe a 150-155 or so, put it in and see what happens. If the problem disappears, we are on to something.

By the way, you did install the washer that goes under the main jet, right? Without it, I think fuel can get past the threads, thus making the main jet larger than it really is.

[jforgo]

Last summer had a very similar problem with my Brother-in-law's Girlfriends new to her 1978 R100. Pulled the carbs apart and replaced all the O-rings and other little rubber bits, reset the floats and all was well. Runs smooth as glass and pulls hard from stop till I chicken out. Way more power than she will ever use.

So 2 main things come to mind.

1st. Check those floats and ensure they are adjusted just right. If too low, then you will get to much fuel dumped in all at once, which will cause sputtering, etc.

2nd. Check all the little rubber bits in the carbs. All the O-rings, etc. All it takes is a very small imperfection and it can cause no end of headaches. For what they are worth, I replace them pretty regularly, about every 2 years, just to be on the safe side. This is especially true if bike sits for any length of time, like over the winter.

One other thing, from what RPM are you doing the hard acceleration? Anything below 2500RPM and you should expect it to stumble and stutter - We used to call it Bogging down. Basically the engine may not be turning over fast enough to accept all that extra fuel and will stumble until it can get to a high enough RPM to be able to accept it. These bikes do like their revs.

On my R100RT, if I have the revs below 2500RPM and need to accelerate quickly, I always punch it down a gear to get into the power band. Usually likes to cruise at 3000 or above.

The carbs were rebuilt by PO. Nice new rubber inside when I changed out the main jets. The floats are pearly white.
The diaphragms looked OK, no tears etc, but i did replace them anyway, since I keep a set lying around and these symptoms are often of diaphragms. . The EUBMW ones are a bit thicker, it seems, than those I removed.
When I roll on, it is anywhere from 3-6K - same problem. More initial surging from higher RPM b4 ssputter sets in. I typically stay above 3K anyhow at all times.
the weird thing is, i did a 5mile loop, twice, at 6000-6800 continuous. As long as I eased up to that speed, no problem. Sounded fine, ran smooth.

[jforgo]

jforgo:

By the way, you did install the washer that goes under the main jet, right? Without it, I think fuel can get past the threads, thus making the main jet larger than it really is.

i do not recall seeing a washer under the main jet. I will have to double check that. I recall main jet, some holey thing whatevr u call it, and something which screws in, and has a large washer, and also an Oring.

The bike had 135 mains in it - PO must have used later 32mm spec. I had thought that was the problem.

i have a nice steep hill near here. Great for road testing stuff. If your vehicle has issues you won't make it over. The bike could barely get over that; coming back i did low throttle with longer run on return, and it did do better.

The surge sputter seems like it is fuel starving. I am wondering about the bowls/floats. New floats would tend to keep less fuel in bowls, i would think.

[tghsmith]

you may have your fuel level in the bowls a tick low(starves for fuel on hard throttle untill the bowl starts to refill)

[fracture]

Main jets of 135 in a bike of your vintage? Way too small. I would like to know what the PO was trying to accomplish. I had an '84RS and it had 160 mains.

Usually, lean surging (such as on oilheads) manifests itself at partial throttle openings. I suppose if it was way too lean you would feel it at all throttle settings.

Fuel starvation, as mentioned by someone else, could also be the problem. I had a clogged fuel filter on an old pickup. Under high demand, like going up a hill, it would sputter. Ran fine with a new filter.

It would appear that fuel delivery is the problem. Either too much or not enough. We have to figure out a way to determine which it is and go from there. The symptoms were there when you got the bike from the PO, right? As far as you know, the carbs are now back to factory specs, right? It sputtered with the 135 mains, that would indicate too lean. But, you put in 160 mains and the problem persists. Maybe there are offsetting problems here.

What about needle jet size? Do you know what size it is? Also, the PO could have changed the needle. I think the tapers are different depending on specific application.

We need to find a way to determine if it is too rich or too lean. I had similar symptoms as yours when I made some breathing improvements that required larger jets. I have a monolever airhead, originally set up very lean with 135 mains. I put in a main that was too big. A smaller one solved everything. So, that is why I suspect too rich at high throttle settings.

[Bill Burke]

Two questions:
Do both throttle cables have 1-2 mm free play at the carbs?
Do both choke (enrichener) cables fully close the choke lever at the carbs when the choke lever at the handlebar or airbox is fully closed?

[jforgo]

The bike did have the roll on issue when i got it.

I did check the needle jet when i replaced the main - was per spec.

I think I should lower these new looking floats.

Also, I am wondering if the advance is crudded up? Maybe pull and clean the can. this doesn't seem like ignition, but still....

[jforgo]

Two questions:
Do both throttle cables have 1-2 mm free play at the carbs?
Do both choke (enrichener) cables fully close the choke lever at the carbs when the choke lever at the handlebar or airbox is fully closed?

The chokes do drop down all the way. Not sure of measure on throttle - there is some slack - since teh bike idled so nice i returned them to the same measured setting after pulling domes and replacing diaphragms.

[Bill Burke]

The chokes do drop down all the way. Not sure of measure on throttle - there is some slack - since teh bike idled so nice i returned them to the same measured setting after pulling domes and replacing diaphragms.
1. Not that I'm the doubting type, but you've confirmed that both choke levers at the carb are fully down by trying to manually press them down further AFTER you've moved the choke control lever to the off position?
2. On the throttle cable question, the goal is equal freeplay on each carb. Lift each throttle cable at the carb until you get some resistance. Compare the sides.
If you get immediate resistance, you have no freeplay. If they're unequal, adjust the freeplay at the carbs to achieve about 1-2 mm. One way to test if you've got enough freeplay is to idle the engine and turn the handlebars stop to stop and see if your idle speed changes. Apologies if this is all old hat.

[Bill Burke]

If it isn't cables, be sure to spray for vacuum leaks at the rubber hoses (carb to head), and then you're into checking for a blocked idle passage(s) in the carb bodies or loose enrichener cover screws. HTH

[Guenther]

The only thing that changes quickly with opening/closing the throttle quickly is the vacuum in the carburetor. Let me think that either the jet needle gets stuck because the jet needle or the needle jet are causing this or, it still is the diaphragm. Or the piston attached to the diaphram gets stuck. Maybe the spring that pushed that piston down. Take the intake tube off and try to slide that piston up with your finger and watch for the slightest resistance.

I would replace the jet needles/needle jets. They are not expensive and wear out over time.

I once replace the diaphragms and while the engine ran fine in idle it did all weird things under load. Turned out the diapgram on one site had turned and hence that piston was out of alignment.

/Guenther
(speaking from experience with a R100GS Bing 64/32)

[mmmalmberg]

Would not hurt to do some full throttle plug chops, perhaps on your big hill...

[Bill Burke]

Or the piston attached to the diaphram gets stuck. Maybe the spring that pushed that piston down. Take the intake tube off and try to slide that piston up with your finger and watch for the slightest resistance.

I agree. Start with the right side carb, where the carb slide can be subject to sticking because the oil breather system sends oil film into that side and varnish can build up causing the slide to hang up. If the slide is sticky, remove the top and spray out with carb cleaner.

[jforgo]

First, the left float was in fact way too low. So i adjusted that up. However, bike still had the crapping out. Rechecked timing, which was OK, both advance and idle.
lAlo, the chokes are bottoming out.
But I checked the coils, and they both had secondary resistance considerably below spec
I see where motorrad offers "blue" coils, but says they are only for points bikes - not for electronic.
Any ideas on the coilss for source?
Also, could this be the cause of the high RPM crapping out?

[Radar41]

On my 82RS, I am having a surge/sputter when I roll on hard.
Valves are adjusted.
Plugs have correct gap.
Idles beautifully.
Thought it might be diaphragms, so I just replaced those.
Bike came with too small main jets - went back to spec 160.
Needle was too high, reset to 2d position per spec.
New air cleaner.
Air injection system is gone.
Air tube connections are tight.
In line and in petcock filters clean.
Under tank trigger unit cleaned, heat sink coating renewed, connections cleaned
If I slowly run throttle up, then bike runs fine continuous for several minutes @ 6800 - so I do not suspect ignition can - or fuel flow.
No visible arcing under tank at night.
Surge/sputter persists.

ideas, o wise ones?

I don't see where you checked the timing and advance unit? Maybe I missed it.

:german

[jforgo]

I don't see where you checked the timing and advance unit? Maybe I missed it.

:german

See post above. i did that belatedly since i was able to run steady highR's, as long as i crept up[

[tghsmith]

call euromotoelectrics..... has coils ....

[jforgo]

So the coils could be culprit in thsi?

Also, bike has some sort of afrtermarket muffler. Could this be a cause?

[tghsmith]

do you have a stock airfilter or k&n ?

[jforgo]

Stock flat airfilter. No pulseair

[tghsmith]

try adjusting the floats to give just a little more fuel in the bowls(correct level can be fidely!!!), check the choke cover screws for tightness, make sure all coil connections are good ,clean and tight, wires not pulled away were they connect to the lug terminal...

[Guenther]

I am no expert but just holding my hand onto the intake of such a combustion engine tells me there is a lot of airflow into the carburetor. And so over the atomizer on top of the main jet. I cannot imagine that setting the float a bit higher/lower would make any difference in the amount of gasoline mixed into the air stream. It's enough to make sure the float closes the valve beform gasoline spills out the vent pipe and that gassoline level does not fall below the main jet level.

Therefore no "fidely" thing to do here.

/Guenther

[mneblett]

I am no expert but just holding my hand onto the intake of such a combustion engine tells me there is a lot of airflow into the carburetor. And so over the atomizer on top of the main jet. I cannot imagine that setting the float a bit higher/lower would make any difference in the amount of gasoline mixed into the air stream. It's enough to make sure the float closes the valve beform gasoline spills out the vent pipe and that gassoline level does not fall below the main jet level.

Therefore no "fidely" thing to do here.

/Guenther

While the above remarks are an interesting theoretical exercise, this is yet another case where theory and the real world don't coincide.

The reality is that bowl level can *significantly* influence the mixture and consequent performance of Bing CV carbs boxers -- BTDT, as have countless others before me. Definitely worth doing the "fidely" adjustment to make sure it's right.

[jforgo]

OK, at this point, the coils are testing with secondary resistance below the spec in Clymers, but within the Snowbum specs. Primary resistance is fine. Blue coils are cautioned against for these electronic ignition bikes. Perhaps leave them alone at this time (?)

I did not personally do the carb rebuild. perhaps I should just go ahead and redo that, in case the choke reassembly was messed up. I have done these before.

I am suspicious of the aftermarket exhaust. Could this be a cause? Too little backpressure? Replace with stock?

[fracture]

Do you know what the aftermarket exhaust is?

[fracture]

Forgot to ask earlier. What do the spark plugs look like? A bit black and sooty, or clean with a tan colored insulator?

[keelerb]

95% of carburetor problems are electrical.

Plugs? Wires? Ignition module? Coils? (edit, scratch coils if you've already tested...)

[keelerb]

PS, you might also want to dump the current gas and try a fresh tankful. Ignore that if the problem has persisted over several tankfuls FROM DIFFERENT STATIONS.

[OHScot]

Hose it off see if it gets worse. Hose it off and crack the throttles at night see if you can see any spark leakage. :lurk

[jforgo]

Do you know what the aftermarket exhaust is?

No, I see no name on it. Hmmmm, if they don't put their name on it, what does that tell me?

[fracture]

What does the exhaust system look like? Is there a muffler on each side, or only one muffler? Is it much louder than stock, or about the same?

I do not think that by itself the exhaust is the problem. But, you never know. The mufflers may have been modified internally to affect back pressure.

[jforgo]

What does the exhaust system look like? Is there a muffler on each side, or only one muffler? Is it much louder than stock, or about the same?

I do not think that by itself the exhaust is the problem. But, you never know. The mufflers may have been modified internally to affect back pressure.

There is a muffler on each side. They are a bit louder. Without tearing into them, they sound like glass-pacs.

[jforgo]

PS, you might also want to dump the current gas and try a fresh tankful. Ignore that if the problem has persisted over several tankfuls FROM DIFFERENT STATIONS.

Thanks. I did empty and put in gas from a well-running stablemate. This made no difference.

[fracture]

With a muffler on each side it does not appear to be a Supertrapp. Supertrapp may have made a 2 into 2 system for that bike but I have only seen a 2 into 1. Is there a series of plates on the back of the mufflers with an end cap, and these plates and end cap held on with screws?

Just wondering about something: Did the previous owner know of this stumbling problem? He may not have known if he never ran at high throttle settings. The problem would never have been experienced.

Was the PO the one who did that carb re-build and changed the main jet and needle position, or someone before him? Is it possible to contact previous
owner(s) to ask a few questions?

Although nothing, including ignition, can be eliminated as a cause until positively ruled out, I suspect carbs. You know that some internal components had been changed and you restored them to factory spec. Something else could have been changed, either deliberately or accidentally, before you got the bike and now there is a problem.

[jforgo]

With a muffler on each side it does not appear to be a Supertrapp. Supertrapp may have made a 2 into 2 system for that bike but I have only seen a 2 into 1. Is there a series of plates on the back of the mufflers with an end cap, and these plates and end cap held on with screws?

Just wondering about something: Did the previous owner know of this stumbling problem? He may not have known if he never ran at high throttle settings. The problem would never have been experienced.

Was the PO the one who did that carb re-build and changed the main jet and needle position, or someone before him? Is it possible to contact previous
owner(s) to ask a few questions?

Although nothing, including ignition, can be eliminated as a cause until positively ruled out, I suspect carbs. You know that some internal components had been changed and you restored them to factory spec. Something else could have been changed, either deliberately or accidentally, before you got the bike and now there is a problem.

No, I can see no plates on the end. i was thinking some "universal fit" except they do have welded on plates with the two matching holes for the bracket.

Yes, I am thinking to just rebuild the rest of the carbs out of hand. Don't know how else to verify choke internals

PO didn't do the carb work - he had the bike a little while and decided he wanted a crotch rocket.

I am suspicious of mufflers, as it seems to me lack of back pressure would come most into play at high revs.

Coil secondary below Clymer spec as far as resistance - but within Snowbum published range. Primary is fine. I am thinking these are OK - higher resistance would seem more problematic.

Should I polish the needle slides with something?

[fracture]

Before taking anything apart, let's step back a bit. At this time I can only suggest a few simple things to look at. We may find something here, or at least, eliminate it as a cause.

You are using good fuel. So, we can eliminate that.

Ignition "appears" to be OK. I am not sure we can eliminate it as a cause, but let's look elsewhere first.

These "mods" were done before you got the bike. Since you mentioned that the air injection system is gone, I assume a PO removed it. Is everything gone, that is, the pipe from head to airbox is gone, the valves in the airbox are gone, etc. This system was vacuum operated. There was a vacuum line from the bottom of each carb to the airbox. The air valves in the air box were activated this way. If that vacuum line was removed, it is necessary to plug that nipple on the bottom of the carbs.

Also, have you verified that there is a washer under the main jet? I was not sure if you had verified that.

Is the pilot jet the correct (factory spec) size? All O rings in good shape?

Again, how do the spark plugs look?

It has been a long time since I have had one of these carbs apart. So, I am not sure about the details of the choke system. I would think that if the choke is malfunctioning and adding excess fuel it would stumble all the time. If the choke is operating properly, a warm engine will stumble badly when the choke is activated. It will not take much movement on the choke lever to flood the engine. Is it possible for you to make this check?

Can't think of anything else to check at this time.

[Guenther]

This has been said in the original post:

"If I slowly run throttle up, then bike runs fine continuous for several minutes @ 6800..."

"As long as it is cranked hard, near or full throttle, the sputter/occasional surge persists."

By this symptom description anything that when there is a quick change would get "stuck" or "clogged".

That could be the mechanical part in the ignition advance unit (THE CAN) or, the pistons in the carburetors. Too much guessing - too little symptom description. :dunno

And 6,800rpms??? I would never do that to my R100GS. :eek

/Guenther

[jforgo]

This has been said in the original post:

"If I slowly run throttle up, then bike runs fine continuous for several minutes @ 6800..."

"As long as it is cranked hard, near or full throttle, the sputter/occasional surge persists."

By this symptom description anything that when there is a quick change would get "stuck" or "clogged".

That could be the mechanical part in the ignition advance unit (THE CAN) or, the pistons in the carburetors. Too much guessing - too little symptom description. :dunno

And 6,800rpms??? I would never do that to my R100GS. :eek

/Guenther

I have an 82 RT which runs well. I am thinking of swapping electrical components piece by piece, like coils and wires, to see what that does.

As to 6800RPM for a few miles to test, that is harmless. You do these a lot more harm idling, like in traffic, or lugging the motor.. These are not Harleys - they are rated for up to 7K continuous. The high RPM test does surface certain issues which a lugster might not catch.

[fracture]

jforgo: When you put the needle back to the factory specified position and installed the 160 main jet, what did that do to the stumble? Make it worse, reduce it, or no change?

[jforgo]

jforgo: When you put the needle back to the factory specified position and installed the 160 main jet, what did that do to the stumble? Make it worse, reduce it, or no change?

I would say it made it worse.

[fracture]

I am trying to determine if we have a mixture problem. This is why I asked what the spark plugs look like. If it is a fuel problem, is it too rich or too lean. And, when the sputter/stumble occurs, is it so bad that the bike can't keep up with traffic and rapidly loses speed, or is it just an "annoyance." The severity of the sputter may tell us something.

You said you have another bike, an '82RT, that runs just fine. You have run this bike at or near full throttle without stumble? Has anyone been in those carbs and changed anything? Do you know what jet sizes are in that bike?

I was working on a possible explanation but it may not hold water if your RT (unlike the RS) runs just fine at factory carb specs.

[jforgo]

I am trying to determine if we have a mixture problem. This is why I asked what the spark plugs look like. If it is a fuel problem, is it too rich or too lean. And, when the sputter/stumble occurs, is it so bad that the bike can't keep up with traffic and rapidly loses speed, or is it just an "annoyance." The severity of the sputter may tell us something.

You said you have another bike, an '82RT, that runs just fine. You have run this bike at or near full throttle without stumble? Has anyone been in those carbs and changed anything? Do you know what jet sizes are in that bike?

I was working on a possible explanation but it may not hold water if your RT (unlike the RS) runs just fine at factory carb specs.

The sputter/stumble on the RS is bad; like barely making it over a large hill.

Yes the RT runs fine at full throttle, all the way to red. I rebuilt the cards after I got it, Orings, diaphragms, floats and float needles all replaced. All jet sizes verified as stock; needle set per manual.

The plug tips look brown; the end of the threads look black.

I wonder about that exhaust...

[fracture]

No doubt this is frustrating. You have two bikes that are mechanically alike yet one runs poorly at the high end of the operating range. I can only make a few more suggestions.

Your spark plugs appear to be fine. At least, mixture seems OK at normal speeds. Hard to tell what is happening at or near full throttle.

If it is possible to do so, can this test be done? Can you take the RS out again and have someone ride behind you? When you get to the stumble point, maybe they can spot black smoke from the exhaust, indicating too rich a mixture.

I doubt if the choke is at fault here but maybe we can use it to try to obtain another clue. Have you verified choke operation? If you add choke to a warm engine, does it sputter? Another possible test is to add choke when you get to the stumble point. If the stumble is reduced, this may indicate too lean, maybe an air leak somewhere.

Normally, an aftermarket exhaust would be less restrictive, thus making an engine run leaner unless jetting changes were made. Without knowing what the exhaust is there may be no way to determine what characteristics it has.

If you are inclined to do so, maybe swap carbs from the RT to the RS. This may not be the thing to do, but when all else has failed.....

If I happen to think of anything I will post it.

[beemerPhil]

Does the bike seem to have more power if you back off the throttle a bit?

:scratch

Early EPA airbox bikes (the first ones with the flat filter and a metal air filter cover) had a severe flow restriction at high rpm/throttle settings. BMWNA went through a string of Service Bulletins regarding various solutions that didn't seem to do anything for my bike or others I was addressing at the time. I found my own answers this way-

:banghead

Stock jets and needle position, except use #50 pilot jets. (45 pilots were never right for the R100, it was an emissions band-aid and made them stumbly and cold-blooded). Clean any oil & water residue from the pilot and main jet air circuits. Be careful with carb-cleaner around Bing CVs- it eats diaphragms if you leave it in there. Run the bike right away to clear the fumes out.

Be sure that your throttle cables are balanced correctly, and that your cold start valves are closing completely. Don't trust the wimpy spring; push the valves shut with your finger. Make sure someone hasn't put the valves back on the wrong sides; they'll fit, but they won't work on the wrong side! It's also possible to put the cold-stgart levers on the cold-start valve shaft backwards- this won't work well either.

Now, take off the air filter cover with the troll horns on it. Put back the air filter, and secure it in place with wire or elastic across the retaining clips. Don't run it with no air filter, even for a minute; the potential downside to this is steep!

Go someplace straight and lonely and open it up. Mine was a different motor without the cover in place, from around 5500 rpm up.


My guess is that your PO with the 135 main jets was trying to compensate for an over-rich condition; he was on the right track, he just hadn't found the source of the problem.


Let me know how you make out. Not all of the early EPA bikes seemed to be affected; of course, how many of those bikes ever got opened up over 5500 rpm?
As far as I remember, the plastic filter covers never had this problem, or had it to such a lesser degree that it wasn't a major issue-


My fix was to cut the horns completely out of the front of the cover, and cover the hole with screen to keep out the bees and mice. The intake was loud, but the bike ran like a bull right to redline!

As always, YMMV......just my .02:dance

[fracture]

True, the PO may have had this same problem and put in the 135 main jets in an attempt to correct a rich condition. Or, it was an attempt to re-jet for higher altitude.

Other things to look for: The diaphragms have indexing tabs on them. If these tabs are not in the slots the diaphragm will not seat well and there will be a leak. Also, is it possible to install the slide incorrectly? That is, can it be rotated so that the circular cut at the bottom is not aligned properly? I think the diaphragm tabs are there to prevent this but I am going from memory here so I can't be sure.

[beemerPhil]

You wouldn't step from 160 down to 135 to compensate for altitude unless you were planning to put the engine in an airplane. Too big a jump. Of course, not everyone with a tool kit knows that.....

:lurk

You could get the diaphragms in wrong, but the perimeter would still be pretty well sealed by the carb lid, which is a pretty tight fit on the body. And you'd have to fight with the diaphragm twice; it has alignment nubs on both the inside and outside edges.

The slides have an alignment groove that engages a guide pin in the slide bore- you could get them in wrong, but you'd have to break off the pins.

It IS possible for someone to break off the pins....but if the bike had that kind of history, it would have other, more severe issues to fix!

:violin

[fracture]

Yes, going from a 160 to a 135 is a big jump. Why so big a jump? No way to answer that as there could be many possibilities. No way to determine what a PO was thinking or trying to accomplish.

We are considering the possibility that a PO was trying to correct an over rich condition with a smaller main jet. The source of this over rich condition, if it did/does exist, has not been found.

It has not been determined if this stumble is due to too rich, too lean, or ignition related. Until this has been determined we can't do much but guess.

[jforgo]

True, the PO may have had this same problem and put in the 135 main jets in an attempt to correct a rich condition. Or, it was an attempt to re-jet for higher altitude.

Other things to look for: The diaphragms have indexing tabs on them. If these tabs are not in the slots the diaphragm will not seat well and there will be a leak. Also, is it possible to install the slide incorrectly? That is, can it be rotated so that the circular cut at the bottom is not aligned properly? I think the diaphragm tabs are there to prevent this but I am going from memory here so I can't be sure.

I replaced the diaphragms, and the tabs are aligned correctly. As such, it does not seem possible to put the slide in wrong.
I could replace the slide needle out of hand.

Since I never like to rule out mere stupidity as a rationale for something being done, the 135 jet would have been applicable to a later monoshock with 32mm carbs. Maybe someone looked at the wrong spec?
The bike came from near sea level - I live a mile high.

The idea of taking off the airbox lid and running is simple and intriguing. I have to see what i have to secure filter.
it does blow black smoke revving in garage

[fracture]

A 135 main jet in a monoshock R100 with 32mm carbs is factory spec. To put that jet in an R100 of '82 vintage with 40mm carbs is pretty lean.

You mentioned that the RS idles OK. The problem is at the high end. You say that the RT runs perfectly from idle to wide open. If you have a chance to do this, compare the idle mixture screw settings between the RS & the RT. From fully seated closed, how many turns do you count? No two are perfectly alike but they should be close to the same.

[jforgo]

OK, I pulled the air filter cover off, and ran it on the lift last with the uncovered filter. Ran up to 6500 - no sputter etc at all!

I had also checked the idle mixture screws - they were at 1 1/4 turn spec.

This seems to clear the electrical part of the equation.

Now I am thinking to just pull the carbs and replace the Orings - even though this appears to have been done - in process maybe I will find some crud?

Or just reset needle to first position?

[beemerPhil]

Does it still blow black smoke revving in garage ? or is the problem resolved?

:dunno

Ride it!

[tghsmith]

sounds like your getting there, make sure all of the lower passages in the carbs are clean, no shreds from old orings and the like. double check the float levels.. 81-84 r100's like a higher level than other bikes,, light flywheel they rev faster than earlier 100's remember the float bowl was designed when 750cc was a big motor and was never changed..

[jforgo]

Does it still blow black smoke revving in garage ? or is the problem resolved?

:dunno

Ride it!

I saw no black smoke

[jforgo]

sounds like your getting there, make sure all of the lower passages in the carbs are clean, no shreds from old orings and the like. double check the float levels.. 81-84 r100's like a higher level than other bikes,, light flywheel they rev faster than earlier 100's remember the float bowl was designed when 750cc was a big motor and was never changed..

i did reset the float bowls for 28mm depth before.

I guess go thru carbs and replace Orings

What would consequences be of doing first position on needle?

[tghsmith]

I would stick with the factory needle position, untill the surging is sorted out, I used to play with different jet sizes and needle positions(all the way down, and such) came to the conclusion that for general all around performance stock jets and settings plus good clean carbs with fresh o-rings made life much better...

[fracture]

Running it in the garage with no load on the engine may not tell you the whole story. Can you ride it with the air filter cover off?

No more black smoke may mean that with an airflow restriction removed by taking the air filter cover off the mixture has been leaned.

I was looking to see if the idle mixture screw settings on your two bikes were the same or considerably different.

If both bikes (RS & RT) have the same idle mixture screw setting then that may eliminate the choke as a possible problem source. If the RS needed to have the mixture screw turned in much more than the RT in order to idle properly I think that would mean fuel is getting in somewhere else. The choke is the most likely source. I do not know of any other way for fuel to get in other than the idle circuit, the choke, and the main jet-needle-needle jet circuit.

[beemerPhil]

+1 to both the above posts- I want to hear your ride-test results!

Because I think it sounds like you're there. Those damn covers were a nuisance for riders who used the throttle; tie down the filter and see what you've got on the road!

[jforgo]

+1 to both the above posts- I want to hear your ride-test results!

Because I think it sounds like you're there. Those damn covers were a nuisance for riders who used the throttle; tie down the filter and see what you've got on the road!

Yes, but I ride in the rain. i need a fix other than running the filter topless!

[fracture]

I am beginning to wonder if the jetting is simply too rich for your elevation and density altitude. My conclusions may be incorrect but I will offer this for discussion.

With the 135 main jet and the needle in other than factory spec position you had a stumble, a sputter, at or near wide open throttle. It is quite possible that what you experienced was fuel starvation. The 135 main jet is pretty small even for the elevation where you are. You would never notice this at less than wide open, or near wide open, because the needle and needle jet are the main fuel delivery control in this range. There would be enough fuel available, maybe just barely, at normal running but not nearly enough at high demand.

With the 160 main jet and the needle in factory spec position you still had a stumble and sputter at or near wide open throttle. It may now be too rich for your elevation. There may have been an overcorrection.

You state that there is no more black smoke when running in the garage with the air filter cover off. Has the mixture been leaned enough with the air filter cover off to eliminate the smoke? Maybe. But, this makes me wonder if the main jet is just a bit too big.

What is the density altitude in Reno now? What is the ambient temperature? Maybe 80 or 85 degrees F? If there are any private pilots out there they may be able to do a calculation to determine just how much the air density has decreased under your atmospheric conditions.

If you do in fact have an over rich condition, there is a possibility that there is a leaking O-ring or some other internal leak. We cannot dismiss this possibility until certain that all internal components are OK.

I have had to experiment with jetting changes on my monolever airhead. A change of just 5 points in jet size (i.e., going from a 160 to 155, or from a 150 to 155) makes a very noticeable difference.

It would be nice if you could ride it with the air filter cover off. It would be interesting to see what happened to the stumble, if anything.

[jforgo]

I am beginning to wonder if the jetting is simply too rich for your elevation and density altitude. My conclusions may be incorrect but I will offer this for discussion.

With the 135 main jet and the needle in other than factory spec position you had a stumble, a sputter, at or near wide open throttle. It is quite possible that what you experienced was fuel starvation. The 135 main jet is pretty small even for the elevation where you are. You would never notice this at less than wide open, or near wide open, because the needle and needle jet are the main fuel delivery control in this range. There would be enough fuel available, maybe just barely, at normal running but not nearly enough at high demand.

With the 160 main jet and the needle in factory spec position you still had a stumble and sputter at or near wide open throttle. It may now be too rich for your elevation. There may have been an overcorrection.

You state that there is no more black smoke when running in the garage with the air filter cover off. Has the mixture been leaned enough with the air filter cover off to eliminate the smoke? Maybe. But, this makes me wonder if the main jet is just a bit too big.

What is the density altitude in Reno now? What is the ambient temperature? Maybe 80 or 85 degrees F? If there are any private pilots out there they may be able to do a calculation to determine just how much the air density has decreased under your atmospheric conditions.

If you do in fact have an over rich condition, there is a possibility that there is a leaking O-ring or some other internal leak. We cannot dismiss this possibility until certain that all internal components are OK.

I have had to experiment with jetting changes on my monolever airhead. A change of just 5 points in jet size (i.e., going from a 160 to 155, or from a 150 to 155) makes a very noticeable difference.

It would be nice if you could ride it with the air filter cover off. It would be interesting to see what happened to the stumble, if anything.

i live at 5200'. But my 1982RT carbs are all set up per stock specs, except the mixture screws are a tad farther out. That bike does fine - even two up going over Sierra passes. These 40mm Bings, on all my bikes besides R65, seem pretty adaptable.
With the aftermarket exhaust, shouldn't the RS do even better?

[fracture]

It would be nice to know what that aftermarket exhaust is. It may have an influence on what is happening.

The fact that your RT runs fine with settings identical to the RS does confuse things. It looks like we are not there yet.

So far, indications are that there is an over rich condition. This has not been proved yet, but the fact that the black smoke is gone with the air filter cover off would lead us to that conclusion. Still, we do not know for sure.

Again, I think it would be worth the try to run without the air filter cover, or try a smaller main jet. Some type of test has to be run to help us with a diagnosis.

[beemerPhil]

My fix was to cut the horns completely out of the front of the cover, and cover the hole with screen to keep out the bees and mice. The intake was loud, but the bike ran like a bull right to redline!


I sold this bike years ago or I'd send a picture- I went straight across the front of the cover below the intake horns, and around the front above them, with a dremel cutter wheel.

It took a while, but the result was worth it. Of course, the newer plastic cover wasn't available yet......besides, I was pissed at those damn horns, and at BMWNA for leading us such a ridiculous chase over the whole thing. You could ventilate the cover any way you like and achieve the same thing.

Try riding the bike with the cover off- if it's all good, try swapping the cover off of your other bike(I assume it's the newer plastic one, since it's giving you no trouble?) If it still runs as it should, get yourself a plastic cover, and case closed.

FWIW, the earlier R100s had a similar problem, and a similar fix- after '78 or so, they all had a group of holes drilled in the back of the pre-EPA airboxes- you could do the same with a hole-saw and save the $$ for a new lid. Just do something about bees and mice, they like it in there!

:dunno

If enough water gets under your gas tank while you're riding to cause any trouble getting into your engine, you'll need to think about getting a taller bike!

:blah

[jforgo]

Try riding the bike with the cover off- if it's all good, try swapping the cover off of your other bike(I assume it's the newer plastic one, since it's giving you no trouble?) If it still runs as it should, get yourself a plastic cover, and case closed.

:dunno

If enough water gets under your gas tank while you're riding to cause any trouble getting into your engine, you'll need to think about getting a taller bike!

:blah

Well, the 82 RS and RT both have the plastic covers

[beemerPhil]

Tried swapping the covers yet?

Either one cover has a bigger "throat" than the other, or one bike has bigger "lungs" than the other- doesn't really matter which, you just need to make them both breath properly.

[Guenther]

I run my R100GS from 6,800ft (my ground zero) to 12,000 ft all with stock settings and no problems. C'mon guys, the engineer(s) who decided the stock settings did something right. Why try to be smarter?

I am still not clear on the symptom mentioned in the original post. Is it this "surge/sputter", still? Only at high rpms? How high? And it only does it when quickly opening the throttle? No matter how, it always does this after a while on higher (how much) rpms?

Without getting a better idea on the symptoms I recommend to get everything to stock settings and thouroughly inspect the ignition system and the carburetor.

/Guenther

[beemerPhil]

C'mon guys, the engineer(s) who decided the stock settings did something right. Why try to be smarter?

/Guenther

The engineers weren't neccessarily riding the bikes under the same conditions; witness the 1985 K100 footpegs recall.

The engineers also sometimes had other considerations besides how the bikes actually ran in the field; witness the early 80s R100s with 45 pilot jets. Or the first Wehrle diode boards.


Overall, BMW does a very good job with these bikes; I think this goes without saying. If they didn't, we wouldn't all be on this forum! But, over the years, there have been more than a few instances where we've found solutions in the field that worked better one way or another than what the engineers shipped out. BMW's experts are no more infallable than anyone else's; and even if they were, given their routine stubborn refusal to openly address persistent issues with various models, even with their certified technicians at BMW Service School, it would be difficult to make any practical use of their expertise. We've been left to find our own solutions, with little if any actual support from BMW, and over the years that's what's happened.

Can you say ring seating? diode boards? fuel lights? valve seats? rear drives? nivomat? stiction? rear main seal? and on and on.......

:scratch

Engineers? Bah! Humbug! Most of the solutions to all of these and many more like them were discovered in the field by people who had already called BMW with relevant questions and got no answers.

:banghead

They do a great job, maybe the best in the business, but the final word, the be-all and end-all, they are not.

:dance



In this instance, we're trying to pin down why one bike seems happy with stock settings, and one apparently identical bike isn't. The airbox cover is an area that's caused this same problem on some bikes in the past, and so far his reported test results, though incomplete as yet, seem to support this theory. I agree that the basic stock settings are a good place to start, but there are areas where we know changes that work better; hence my recommendation for stock jets except for the anemic #45 pilot jets. #50s run better!
Someone put 135 mains in this bike; possibly because they were trying to compensate for air-starvation at full throttle, which is symptomatic of the airhorn restriction I'm discussing. Also possibly because they took the carbs apart on the same bench as some 32mm carbs and got the parts mixed up; we can't know this for sure, we can only work with what we have.


Quite sure, now, that this horse is dead. But anybody can kick it again who wants to......