75/6 high idle speed and ignition mysteries...

[wlovin]

I just picked up my new for me 1975 R75/6. Neat ride home. Very different from my K bike. Anyway, along my route I noticed that idle speed had drifted up to the 2200 rpm level. Otherwise it was running beautifully...

I got home, consulted the BMW oracle or all oracles - this forum - and noticed that stuck timing advance weights are a prime candidate for causing this kind of problem.

So today, I popped off the engine front cover and observed that the timing advance weights didn't appear to be stuck, they seem to move rather freely, the springs are intact, the lube felt doesn't seem like its doing much though.

There is however a rubber conduit that leads from the breaker compartment to the condenser above the alternator (it protects the condenser wires) and I noticed that it is cracking from age where it clamps between the engine front cover and the engine. It *might* have been interfering with the operation of the weights.

So I consult my online part resources and note that the rubber conduit doesn't seem to be on the fiche (at least on the engine electrics/ignition fiche I was looking at). Also, there's a small rubber gasket or o-ring (I guess) that seals the rotor/breaker compartment from the rest of the front cavity. It's not visible on the fiche either.

So question one: does anyone have a part number (or work-around -something like RTV and Permatex blue gasket compound) for the rubber conduit and/or rubber gasket or o-ring. Or should I just get real and forget them?

Question two: my Haynes references several different kinds of ignition grease (Bosch Ft 1v4 and 1v22 or 1v26) to be used on the weights, cam follower, etc. Isn't there one ignition grease I can buy OTC at my local auto supply store that will do the same thing??

TIA,

Bill Lovin

[88bmwJeff]

So today, I popped off the engine front cover and observed that the timing advance weights didn't appear to be stuck, they seem to move rather freely, the springs are intact, the lube felt doesn't seem like its doing much though.

Unfortunately, I can't help you with the proper type of lube, but If you're new to old boxers, make sure you disconnect the battery before removing the front cover. You can short things out that way.

Other good sources of information are

www.boxerworks.com (message boards)

http://w6rec.com/index.html

[wlovin]

Lash me for asking the forum too fast about two part numbers I could have gotten on my own. I should have checked A&S's microfiches first...

B. Lovin

[cjack]

I just picked up my new for me 1975 R75/6. Neat ride home. Very different from my K bike. Anyway, along my route I noticed that idle speed had drifted up to the 2200 rpm level. Otherwise it was running beautifully...

I got home, consulted the BMW oracle or all oracles - this forum - and noticed that stuck timing advance weights are a prime candidate for causing this kind of problem.

So today, I popped off the engine front cover and observed that the timing advance weights didn't appear to be stuck, they seem to move rather freely, the springs are intact, the lube felt doesn't seem like its doing much though.

There is however a rubber conduit that leads from the breaker compartment to the condenser above the alternator (it protects the condenser wires) and I noticed that it is cracking from age where it clamps between the engine front cover and the engine. It *might* have been interfering with the operation of the weights.

So I consult my online part resources and note that the rubber conduit doesn't seem to be on the fiche (at least on the engine electrics/ignition fiche I was looking at). Also, there's a small rubber gasket or o-ring (I guess) that seals the rotor/breaker compartment from the rest of the front cavity. It's not visible on the fiche either.

So question one: does anyone have a part number (or work-around -something like RTV and Permatex blue gasket compound) for the rubber conduit and/or rubber gasket or o-ring. Or should I just get real and forget them?

Question two: my Haynes references several different kinds of ignition grease (Bosch Ft 1v4 and 1v22 or 1v26) to be used on the weights, cam follower, etc. Isn't there one ignition grease I can buy OTC at my local auto supply store that will do the same thing??

TIA,

Bill Lovin

First of all, the part number for the rubber tube is 11 14 1 253 415
The part number for the rubber gasket around the points is 11 14 1 265 394
You weren't looking in the right place on the fiche. BMW almost seems to hide things...but they are there...somewhere. If you have been reading the fiche for a while, you will catch on to their madness.
Do not mess up the area with excess rtv, etc. Glue the gasket seal (comes in a string about 9 inches long) in with something like that contact yellow glue or such.
When the dealer orders the gasket material, it comes in bulk. I don't know if they really know how to measure it and the last time my dealer ordered it, they got a big coil of it. If you don't have any favorites, call Twin City BMW in Savoy, IL and order (217-356-0399). They ship ups every day and charge only actual shipping. They have this kind of stuff in stock...and many other airhead maintenance parts. I part time there, but only because I want to make sure they have plenty of parts and accessories in stock...heh.
They use one grease for the points block (pad) and one for the cam shaft under the advance unit. I don't think it is terribly sensitive. Be careful with the nut that holds on the advance unit. Many have busted off the end of the cam shaft by over tightening. Just snug it up. I don't like torque wrenches for small threads like that unless you have a sensitive one for low torque values.
Treat all aftermarket manuals with caution. Check their advice with BMW owners and techs before proceeding with their take on it. Especially things like torque values, etc. Make sure it makes sense.
If the advance doesn't do it, then check the valves first, cold, then check the carburetors for sync and idle air setting. Especially check the choke housing (probably first before anything else for your problem) with the four screws on it. They can be loose and if they are, the choke housing cover gasket could be sucked into the housing. Leaking.

[cjack]

Unfortunately, I can't help you with the proper type of lube, but If you're new to old boxers, make sure you disconnect the battery before removing the front cover. You can short things out that way.

Other good sources of information are

www.boxerworks.com (message boards)

http://w6rec.com/index.html

By the way, BMW recommends you remove the ground cable at the battery end, rather than at the transmission vent screw because it is so easy to strip that screw.

[pmdave]

General advice on airhead ignitions:

Those little springs retract the weights, which retards timing. At idle the weights should be fully retracted. As the engine spins up, the weights fly outward (stretching the springs) and advance timing for higher RPMs. So, check that the springs pull the weights back all the way. I don't know if the springs are still available, but they used to be a separate part available from the dealer.

If the springs are stretched--or just worn--the timing will be advanced at idle. Check the timing with a strobe light. For 1970 to 1978 models, dynamic timing is correct when the line above the S is even with the notch in the window, with RPM 800 or less.

If not, adjust the points to get the bar aligned.

Rev the engine observing the S dissapear at about 800 RPM. At around 2,800 RPM, the F mark should appear in the center of the window. This indicates the advance mechanism is working correctly.

The smallish points in pre-80 (possible pre-79) engines are tricky to set, because just tightening the plate screw changes the gap. AND if you've been running the engine, those exhaust headers are hot hot hot and in the way. Take your time, and you'll be able to figure how to adjust the points slightly narrow or slightly wide, and get the ideal gap as you tighten the screw.

The 1980 (and possibly some '79) used a "can" that contains the points and advance mechanism. The same "can" got electronic-ized in 1981. But the "can" is removable, and that makes it easy to service off the bike. The ignition points are also much larger than the older versions, which helps them maintain gap. Adjusting timing is also a snap because you just rotate the can while watching the timing marks--similar to an automobile.

If you see a double image of any of the marks, that indicates a bad advance mechanism. Be forwarned that you'll prefer fixing your old part and only pricing a new advance if all else fails. Sit down before asking the price. Next time you're nosing around a swap meet, look for a spare advance mechanism.

There is nothing special about the vent tube to the points cavity or "can". Any piece of rubber tube should work fine. The stock part tends to get hard with age. If you can't find the grommet that seals the tube to the case, get some epoxy paste and make your own grommet. Be sure there is no excess material on the inside of the hole that could interfere with the advance. A vent tube in good condition helps keep water out of the points.

If you find the points in good condition (no pitting or spike) continue to use the same capacitor ("condensor"). If you find the points burned, pitted, or with a spike, change the condensor.

You can check the dwell with a dwell meter (ideal = 120 degrees), but with only two cylinders I don't think dwell is very important. I think it's more important to have correct points gap (0.016" will work for all models, but for '79 - 80 R65, 0.018" is suggested) and spot-on ignition timing. I've never used a dwell meter on an airhead.

With pre-1980 models, NEVER use the nut on the end of the camshaft to turn the engine. With the plugs removed, you can use a hex wrench in the bolt on the alternator rotor to turn the engine. Recently, I've drilled a hole in the front cover of my R100, directly in front of the alternator bolt. The hole is covered with a rubber timing hole plug. Easy access to the bolt is helpful for setting valves.

It's OK to run the engine with the front cover removed, but always disconnect the battery ground wire before removing or installing the cover. If you're going to run the engine more than a minute or so, put a couple of electric fans in front of the cylinders to provide cooling air.

My '80 R100 sometimes idles fast when warm. I've checked, prodded, rebuilt, fixed found problems, adjusted, twiddled, diddled, and fiddled, and it just does this. I don't know why.

pmdave

[Bob_M]

General advice on airhead ignitions:

My '80 R100 sometimes idles fast when warm. I've checked, prodded, rebuilt, fixed found problems, adjusted, twiddled, diddled, and fiddled, and it just does this. I don't know why.

pmdave

My 84 R100 runs great, but it also idles fast when warm. I had planned to twiddle this weekend, but apparently it does no good. :dunno

[R100RS]

Try this test next time the idle won't drop down...

At rest with the engine running and the bike in neutral, grab the ignition switch and turn it to off. Just before the engine dies, turn the ignition back on. If it idles normally, the problem is in the advance mechanism. Alternatively, you can hold the brake and let the clutch out slowly while in gear, then right before it stalls, grab the clutch in full again.

So, if the problem is in the advance, remove the advance unit, disassemble it and lube it up, including some oil where the felt rubs against the shaft. DO NOT OVERTIGHTEN the nut on the front of the crankshaft that holds the advance unit on. It doesn't have to very tight at all - a smidge more than hand tight. It's easily stripped and if you do that, you are in deep deep doggy doo. Don't forget to disconnect the negative lead at battery before pulling the front cover.

If, after lubing the advance mechanism you still experience the problem, you will need to replace the springs. These are available separately, but are pricey - around $10 each. You'll need to replace them both.

[cjack]

General advice on airhead ignitions:

My '80 R100 sometimes idles fast when warm. I've checked, prodded, rebuilt, fixed found problems, adjusted, twiddled, diddled, and fiddled, and it just does this. I don't know why.

pmdave

Choke circuits?
Anyway the advance unit goes for $294 these days and the can appeared as of 10/78 build date according to the fiche.
If the advance is greased and operating freely, I never had any problem with it not going back to idle. So I don't think weak springs as R100RS suggested above. I suppose, but never saw that happen. Usually, other than the advance unit being sticky, it was the choke circuits causing fast idle.

[wlovin]

Other posts on the forum reference the miniscule torque with which the advance mechanism is attached to the camshaft. Also, I noticed when I backed the nut off there was very little release torque. As you say, I've been warned, warned, warned!

The springs seem to retract the weights OK. There is more "slop" in the whole assembly than I would have thought possible, but I guess that's to be expected since the whole thing is really tied together by being mounted on the camshaft. So, I will first disassemble, clean, and lube the whole mechanism, and then proceed through the entire tune-up procedure.

The guy I bought it from seemed to know his stuff. Particularly the part about adjusting the valves twice as much as you think you have to. Also,this thing is in stunning shape for a '75, so I'm sure it's been properly sorted out by its previous two owners.

Thanks for the part numbers. You are right, I was on the wrong fiche. :banghead

I did disconnect the battery before removing the cover, but now that I think of it, that make me wonder *what* is energized on the bike with the key off??? When you say things can get shorted I assume you mean the diode board? Or is there something else in the electrical system that can get blitzed, too?

Thanks again!,

Bill Lovin

[PGlaves]

The two main causes of a fast idle are either the advance mechanism sticking or an induction air leak. The easiest way to tell the difference is to pull the idle speed down by loading the clutch as described above. If it stays down it is pretty sure to be a sticking advance. If it goes back up by itself it is virtually certain to be an air leak. Typical locations are the rubber connections between the carbs and the heads, the gaskets where the enricheners (chokes) attch to the sides of the carbs, and occasionally the shaft seals (O rings) on the throttle plate shafts.

There are a number of other obscure causes of the idle speeding up significantly when the engine is hot compared to when the engine is cold. Often it is a symptom of the idle speed being set too high to start with, because the engine runs poorly when cold. So somebody cranked up the idle speed so it doesn't keep dying when cold.

I would first rule out the advance mechanism by making sure it is working correctly. Second I would make sure there were no air leaks at or downstream from the carburetors. If neither of these seem to be the cause I would try to determine what tuning elements - plugs, wires, valves, jets, enricheners, etc. - may be causing a low cold idle. At least half the time I find a curable low cold idle is the root of the apparent high idle problem.

[cjack]

I did disconnect the battery before removing the cover, but now that I think of it, that make me wonder *what* is energized on the bike with the key off??? When you say things can get shorted I assume you mean the diode board? Or is there something else in the electrical system that can get blitzed, too?

Thanks again!,

Bill Lovin

Folks worry about shorting the cover to the battery positive on the diode board while touching ground at the same time. I think that's about it. Actually the whole bottom metal frame of the diode board is +12 all the time. Given the way the diodes are arranged, etc. it does not look possible to ruin the diode board...just make big sparks, etc.

[R100RS]

How do you know it's retracting properly? It will act very different on the bench than in the bike. Is the bike coming down off of advance (check with timing light)? The unit in the /6 I'm working on also felt very sloppy, but it works fine (now).

Another neat way to see what's going on is with it acting improperly: take the bike home and park in a moderately dim place (garage) in neutral, pull the battery negative, pull the front cover, hook up a timing light, reattach the battery, start the bike. Aim the timing light at the advance mechanism and work the throttle around. See what happens. Can also try cutting the ignition off and on as described above. It should be very informative.

I had the exact same idling problem with the /6 I'm rebuilding. One of the advance return springs was bad (and it was in desperate need of lubrication).

Here's another way to check for air leaks:

With the bike idling in neutral, grab a can of carb cleaner and spray it on the outside of the carburetor (especially where the butterfly shafts are) and the outside of the air tubes between carbs and engine. If the engine picks up speed, you got an air leak.

[wlovin]

Jeez, that little square rubber gasket is a PITA to get in around the breaker assembly!

Anyway, got it all together, and it fired immediately using the time honored starting sequence. Through the 60Hz flicker of the flourescent lights in the garage, I could make out that weights were expanding and contracting equally on both sides as I thottled up and down.

As an aside, when the bike first started it idled at 800 RPM (with generator light on BTW) and as it warmed up it slowly floated to up to 1200 RPM. Sounds like unmetered air leaning the mixture out...

Unfortunately its been raining cats and dogs here in Big D so no riding today to check the longer term stability of the idle.

On a separate note, I found a small puddle of hypoid gear oil (perfectly clear with a heavy sulfer smell) under the rear end of the boot between the transmission and the drive shaft. Manual inspection doesn't indicate a torn boot, but suggests that the leak is aft of the clamp that clamps the boot to the driveshaft. Maybe the clamp is too loose.

Anyway thanks to all again. I'll be poking around looking for air leaks..

Bill Lovin

[vanzen]

Just in case:

Be sure the motorbike is THOUROUGHLY warmed up
before setting the idle speed ...
I have seen this problem happen when the carbs are set after just running the engine for a short while in the garage, while tuning -- idle seems fine, but then after a good ride of 20 miles or more, it's idling 2,000+rpm.

take it out for the "good ride" first, then adjust the idle speed.
Your problem may be as simple as that.

[wlovin]

Maybe idle speed is misadjusted and I'm taking it off the choke too soon. Hence the idle at 800-1000 initially (off the choke within 60 seconds of firing) and steady climb to the (improperly) set idle speed as it warms up.

It probably should be adjusted to require the choke to be set at the warm-up position until thoroughly hot, then idle properly off the choke some minutes later...

Thanks, I didn't think of this as something to check!

Bill Lovin

[vanzen]

(assuming valves, timing, etc are right --
that the bike IS otherwise in good tune)

try running the bike till it idles up to that fast idle you speak of.
THEN readjust the idle speed to @ 850 - 1100rpm --
which, I believe, is the spec range.

If the idle speed is adjusted before the engine is THOUROUGHLY warmed up, that FAST idle - once it IS warm - is sure to happen.
think about it: setting the idle speed before the engine is warmed = using the idle speed screw as a choke!
Start the bike and take a ten minute (or longer) ride ,
THEN adjust the idle speed.

Choke needs will vary from bike to bike.
I have seen well tuned 247s that want choke for just a minute, and others that want it for a mile or more.

[wlovin]

Pulled out the timing light and freaked because I was seeing double images at the S mark. Twiddled with the pickup on the light and noticed that by manipulating the pickup I could get either double images or one image rock steady right where it was supposed to be. I'm assuming the pickup is bouncing around on the plug wire or something, because when I hold it steady againt the plug wire the image settles down.

Anyway, looks like proper advance all through the throttle curve with a smooth return to the S mark when the throttle is closed.

So, I've now checked the valves, I know the static timing is pretty darn close, and it still warm idles at 1500 RPM.

My working assumption is that the idle is indeed set too high, so I tuck in and adjust the mixture settings for best idle (nothing changed because they were already set for best idle), and slowly screw out the throttle stop screws until I get to 1000 RPM. The idle is now much "lumpier", so I assume that minute tweaking of the mixture and throttle stop screws will get it closer to best idle.

Of course, I still need to sync the carbs.

Progress, I think, is being made...

Bill Lovin

[vanzen]

hang in there, likely you are on to it!