No vacuum?

[rmarkr]

I dusted the K bike off to give it a tune up. I found next to no vacuum on # 2 cylinder - others were OK. Must be a stuck valve I assumed, but found the compression to be normal (about 150psi). Fitted new plugs - no improvement, pulled the fuel rail and injectors - all were spurting. Pulled the plug cap - the plug was firing energetically, but I was getting a mild shock through the metal cap.
Must be the intake manifold leaking - took a good look at it and sprayed WD40 all around to see if things would change - no such luck. Blocked vacuum take-off pipe maybe? - sprayed oil in there, it came belching out of the exhaust.
The bike is in good mechanical order, when used last, 3 months ago, all was well.
I am sure that this is a no-brainer (I have no brain) Please help.
:type

[deilenberger]

. Blocked vacuum take-off pipe maybe? - sprayed oil in there, it came belching out of the exhaust.
The bike is in good mechanical order, when used last, 3 months ago, all was well.
I am sure that this is a no-brainer (I have no brain) Please help.
:typeI'd suspect the vacuum port might be plugged up somehow. When you say you sprayed oil in there and "it came belching out of the exhaust" - what exhaust?

One other question - just to reassure myself - you haven't twiddled (tech-term) any of the screws that link the throttle-bodies together right?

And how is the engine running? Does it sound like it's missing on one cylinder (which it would be if the ignition wasn't working on that cylinder or a valve was stuck open [VERY unlikely BTW])..?

[98lee]

Just a thought: a bad o-ring on the throttle balancing screw would cause low vacuum (probably not none). It's worth a shot.

Put some grease on your thumb and press it over the head of the balance screw for that cyl. See if the vacuum jumps.

If yes, remove screw (count turns) replace o-ring.

If not, oh well, it was a shot.:dunno


:dance :dance :dance

[rmarkr]

I'd suspect the vacuum port might be plugged up somehow. When you say you sprayed oil in there and "it came belching out of the exhaust" - what exhaust?

One other question - just to reassure myself - you haven't twiddled (tech-term) any of the screws that link the throttle-bodies together right?



Thanks for the responses. A bit more info:
The issue is so bad that if I pull the plug cap off nothing changes (idle speed etc).
If I remove the air screw completely nothing changes. The vacuum port (pipe) is clear - I can insert the straw on the WD40 can into it. When I squirt WD40 into the vacuum port, the idle speed picks up, it appears to burn the stuff, and a cloud of smoke comes out of the tail pipe.
No, I've not touched the idle stop screws, or the butterfly spindle - one thought though - could the flap have come off of the spindle? Would I get symptoms like this. The symtom must have been there before - what caused me to take a look was a light knocking at the rear of the engine at idle speed - I read that poorly synced throttle bodies could manifest like this. I must confess to not realising straight off that there was a complete misfire on one cylinder - the electronics seem to compensate for the problem and the exhaust is well muffled.
The k-bikes.com site describe a similar issue where the manifold 'O' ring (where it seats on the head) was to blame. Hard to believe, but I will take a look at that tonite - I need to strip a good few parts off to get the throttle body assembly out.
To repeat - I do have spark (at twice the firing cycle), and I do have fuel, but I'm not sure that the lack of either would produce the no vacuum symtom.
Thanks again for the input.
Mark
:type

[deilenberger]

Mark,

Before pulling the throttle-bodies off (that WILL require new rubber mounts above and below.. they are old and don't take well to R&R) -

How does the plug on that cylinder look?

Reason I ask - it sounds as if the engine is running OK. If one cylinder wasn't working it would be rather obvious.. and the light knocking you hear at the rear of the engine (usually right side) - is semi-normal for K bike engines. There is a lot on this on the IBMWR K-tech FAQs..

[98lee]

Before you take it apart, check the valve adjustment!!! :thumb

An exhaust valve that is too tight will give you good compression when the motor is not running and low vacuum when it is running ( after it has heated up enough to loose all its lash and hold it open. Exhaust valves tighten up over time (valve recession).

And it would give the slight knocking sound coming off idle. BTDT!

That's my next best guess and I'm sticking to it!!:rocker


:dance :dance :dance

[rmarkr]

Before pulling the throttle-bodies off (that WILL require new rubber mounts above and below.. they are old and don't take well to R&R) -

How does the plug on that cylinder look?

Reason I ask - it sounds as if the engine is running OK. If one cylinder wasn't working it would be rather obvious.. and the light knocking you hear at the rear of the engine (usually right side) - is semi-normal for K bike engines. There is a lot on this on the IBMWR K-tech FAQs..

First thing I did was fit new plugs. They all looked the same - tan colored center insulator, and a little black soot on the ends of the threaded body, no noticeable electrode wear. The suspect plug had been working OK it seems.

I have not checked the valve clearances - they sounded fine and the bike was performing well. After my first assumption about a stuck valve, I was about to pull the cover, and thought that the compression test would verify my diagnosis. The rather casual comp test was performed only on this cylinder, first under cranking only (all plugs out, throttle open - about 150psi) then started the bike and got a reading of about 175psi. Would an open valve be struck by the piston? I shudder to think.

Would I be able to lift off the throttle body assembly with all hoses still connected - the hose clamps are crimped on and would have to be cut to release them - not a pleasant proposition.

I will check the valve clearances, and do a good inspection under the cover. I feel I really need to get a look down the throttle body - again my dodgey assumption leads me there.

Thanks again for the help.
I'll let you you know.

Mark
:scratch

[rmarkr]

Before you take it apart, check the valve adjustment!!! :thumb

An exhaust valve that is too tight will give you good compression when the motor is not running and low vacuum when it is running ( after it has heated up enough to loose all its lash and hold it open. Exhaust valves tighten up over time (valve recession).



Lee,
Your response certainly made me think. My good old assumption was that valve clearance would always increase (from wear) but, I can see that a valve that drops further into its seat will loose clearance, and that the cam, bucket etc is well lubed, while the valve head operates in a very hostile environment, with minimal oil. I'll check the clearances next.
Thanks

[98lee]

Intake: 0.15-0.20 mm (0.006-0.008 in.)
Exhaust: 0.25-0.30 mm (0.010-0.012 in.)


If you have to make an adjustment shoot for:
Intake: 0.006 in.
Exhaust: 0.012 in.

Tight side of spec on intake and loose side of spec on exhaust.

All measurements COLD (head temp less than 95 deg.F.)

Let me know what the exhaust valve clearance on that cylinder was. (inquiring minds want to know).


:dance :dance :dance

[bmwmick]

Lee,
Your response certainly made me think. My good old assumption was that valve clearance would always increase (from wear) but, I can see that a valve that drops further into its seat will loose clearance, and that the cam, bucket etc is well lubed, while the valve head operates in a very hostile environment, with minimal oil. I'll check the clearances next.
Thanks

Mark,
Any rodents around? I'd pull the air cleaner element and look for a restriction in the #2 inlet hose. SOMETHING is causing the 'no vacuum' condition and you've ruled out about everything else.

[deilenberger]

First thing I did was fit new plugs. They all looked the same - tan colored center insulator, and a little black soot on the ends of the threaded body, no noticeable electrode wear. The suspect plug had been working OK it seems.
Sounds perfect..

I have not checked the valve clearances - they sounded fine and the bike was performing well. After my first assumption about a stuck valve, I was about to pull the cover, and thought that the compression test would verify my diagnosis. The rather casual comp test was performed only on this cylinder, first under cranking only (all plugs out, throttle open - about 150psi) then started the bike and got a reading of about 175psi. Would an open valve be struck by the piston? I shudder to think.
A non-adjusted one would have to be VERY out of spec to be struck by a piston. I think this is a non-issue.
Would I be able to lift off the throttle body assembly with all hoses still connected - the hose clamps are crimped on and would have to be cut to release them - not a pleasant proposition.
Unfortunately - no. It's a fairly major job (BDTD) - the clamps all have to be cut off - and usually replaced with the same type of clamp (there isn't room for screw-clamps, and the crimped clamps provide a very accurately controlled clamping pressure) - and I'd suggest replacing ALL the rubber, above and below the TB's. The TB mounts are made of rubber - and they have an O ring embedded in the bottom. AFAIK - that O ring is not replaceable - you have to replace the entire mount. Given the hostile environment they live in (think HOT) - and the age of the bike - the rubber has very likely hardened up, and may have started cracking (my '85 did back around '96.. only 11 years old..)

It's a fairly major job. It took me most of a day to do it - but I did do some other things (had injectors cleaned, some lily gilding, etc) while it was all apart.


I will check the valve clearances, and do a good inspection under the cover. I feel I really need to get a look down the throttle body - again my dodgey assumption leads me there.

Thanks again for the help.
I'll let you you know.

Mark
:scratchSounds good. Waiting to hear what you find.

[rmarkr]

11491
Yes, it is the rubber boot below the throttle body that connects to the manifold inlet tube (injector housing). It looked OK while assembled, and as you say, Don, it is a bitch to get out. I had to destroy two of the crimp-on clamps, the other is a screw-up clamp (lower). The rubber fatigue is serious, and I'm sure the rest are headed south as well.
To find the leak this is what I did. Removed the intake pipe from the airbox and plugged the TB with a rubber crutch tip I found in the garage (stop s******ing in the background), closed the air screw, and blew air (by mouth) through the vacuum take off pipe. I could feel the air escaping, no need for soapy water etc.
This was after checking the valve clearances - they all seemed spot on, cam lobes nice and shiny - no problems here. Depressed the cam followers to feel for any sticking - seemed good. Then I did another compression test on all the cylinders. My readings were 190, 195, 200 195 psi (all spark plugs out, throttle open, engine at about 30 degrees C, cranked with the starter) Seems high, could this be right?
This is a 91 KRS, 37k miles (I've put last 15K miles on it over the previous 18 months - no record of its previous history)
The bad news is that it appears that the offending rubber tubes are pre-installed on the throttle body assembly and are not replaceable, according to my Clymer manual. I'll see what my dealer has.
Thanks again for all the input, it is certainly nice to have the support.

[deilenberger]

Mark.. see http://www.realoem.com/bmw/showparts.do?model=0533&mospid=47924&btnr=11_1822&hg=11&fg=20

I'm not certain (I'm much more familiar with the earlier design..) - is PN-5 what you need? The drawing indicates it's above the TB assembly.. which doesn't make sense to me unless the TB's bolt directly to the head.. (unlikely..) since http://www.realoem.com/bmw/showparts.do?model=0533&mospid=47924&btnr=13_0522&hg=13&fg=15 shows what looks much like the older K bike design - where a rubber tube fastens to the bottom of the TB to go to the head.

Also - a question - you didn't disassemble the TB "assembly" (the four bolted together) to get to this hopefully?

Best,

[rmarkr]

Mark.. see http://www.realoem.com/bmw/showparts.do?model=0533&mospid=47924&btnr=11_1822&hg=11&fg=20

I'm not certain (I'm much more familiar with the earlier design..) - is PN-5 what you need? The drawing indicates it's above the TB assembly.. which doesn't make sense to me unless the TB's bolt directly to the head.. (unlikely..) since http://www.realoem.com/bmw/showparts.do?model=0533&mospid=47924&btnr=13_0522&hg=13&fg=15 shows what looks much like the older K bike design - where a rubber tube fastens to the bottom of the TB to go to the head.

Also - a question - you didn't disassemble the TB "assembly" (the four bolted together) to get to this hopefully?

Best,

Don, yes it is part # 5 that is needed. The diagram is confusing as it appears to show it connecting to the hose from the airbox, but below it is correct, sitting above the manifold (a misnomer) or injector housing. The sequence from the cylinder head up is the manifold, then the "bushing PN5", then the TB and above that the airtube to the airfilter housing.
No, I have not taken the TB assembly apart (I would'nt dare!). I removed the fuel rail and injectors, all the electrical connectors, backed off the screw up clamps on the bushing (PN5), and lifted the whole deal, with air tubes connected, just enough to pull this part off. To remove the TB assembly from the bike, the fuel pressure regulator, which is attached to the back of the assembly, has to be removed. And to get to it the airbox has to be pulled out. (They dont make it easy!) I have not disturbed the manifold pipes.
The good news is that the parts are available (I use Bobs), including the crimp up clamps, which appear to use some kind of open mouthed pliers to pull them up - I'm sure I can find or fashion something to work.
Some bad news - the sticky oil from the fancy K+N filter is on all the inside surfaces, and won't wipe off - found it on the airscrew needle too. I hope its not going to be trouble.
I'm looking forward to having a smooth running machine.

11492

[deilenberger]

Don, yes it is part # 5 that is needed. The diagram is confusing as it appears to show it connecting to the hose from the airbox, but below it is correct, sitting above the manifold (a misnomer) or injector housing. The sequence from the cylinder head up is the manifold, then the "bushing PN5", then the TB and above that the airtube to the airfilter housing.
What I thought..
No, I have not taken the TB assembly apart (I would'nt dare!). I removed the fuel rail and injectors, all the electrical connectors, backed off the screw up clamps on the bushing (PN5), and lifted the whole deal, with air tubes connected, just enough to pull this part off. To remove the TB assembly from the bike, the fuel pressure regulator, which is attached to the back of the assembly, has to be removed. And to get to it the airbox has to be pulled out. (They dont make it easy!) I have not disturbed the manifold pipes.
A very good thing. Don't disturb the screws that connect the TB's together either.. these are set at the factory, and tweaking them on the bike isn't a good thing..
The good news is that the parts are available (I use Bobs), including the crimp up clamps, which appear to use some kind of open mouthed pliers to pull them up - I'm sure I can find or fashion something to work.
KD Tools makes one that isn't awfully expensive - it's basically an end-cutting "nipper" (wire cutter type) where the jaws don't quite come together. This type of clamp is commonly used on CV joints on cars.. they're called Oetiker Clamps. Here is a link to some tools and supplies: http://chadstoolbox.com/index.asp?PageAction=VIEWCATS&Category=521

This particular tool is one I have - and it works fine.. http://chadstoolbox.com/index.asp?PageAction=VIEWPROD&ProdID=7914
Some bad news - the sticky oil from the fancy K+N filter is on all the inside surfaces, and won't wipe off - found it on the airscrew needle too. I hope its not going to be trouble.
I'd suggest ordering the standard paper filter while you're getting the rest of the parts, then take the K&N and throw it as far as you can.. aside from not giving more power - it also gums up the works (as you've seen) and allows more dirt into the engine. The stock filter - due to how it sits in the airbox is good for well over 25,000 miles between changes if you're not going off-road with the bike. K&N = evil IMHO.
I'm looking forward to having a smooth running machine.

11492

Good luck, and take a photo or two while doing the job, it would make a good FAQ for the forum!

[98lee]

No Vacuum? Found the Culprit!!!:thumb :clap :clap :clap


:dance :dance :dance

[bikerfish1100]

I do so love it when DIY meets with JCS (Job Completed Successfully).
Nice perseverance.

[rmarkr]

Intake: 0.15-0.20 mm (0.006-0.008 in.)
Exhaust: 0.25-0.30 mm (0.010-0.012 in.)


If you have to make an adjustment shoot for:
Intake: 0.006 in.
Exhaust: 0.012 in.

Tight side of spec on intake and loose side of spec on exhaust.

All measurements COLD (head temp less than 95 deg.F.)

Let me know what the exhaust valve clearance on that cylinder was. (inquiring minds want to know).


:dance :dance :dance


I must make another embarassing crawl into a crack here. All I had was a feeler gauge in .05mm increments (and an imperial ignition gauge with thick blades) - so it was a 'go/no go' type deal. All the exhausts would take a .25 but not the .30, the inlets took the 0.15 but not the 0.20, except one which was greater but would not take the 0.25. I set out to do a careful measurement of the valve clearances, but had to back off when I took a look at my feeler gauge. I was left with the impression that the valve clearances had been carefully adjusted before I got my grubby paws on the bike. I was relieved as I really didnt want to mess with valve clearances, and focussed on dealing with the intake issue.


:blah

[bikerfish1100]

I must make another embarassing crawl into a crack here. All I had was a feeler gauge in .05mm increments (and an imperial ignition gauge with thick blades) - so it was a 'go/no go' type deal. All the exhausts would take a .25 but not the .30, the inlets took the 0.15 but not the 0.20, except one which was greater but would not take the 0.25. I set out to do a careful measurement of the valve clearances, but had to back off when I took a look at my feeler gauge. I was left with the impression that the valve clearances had been carefully adjusted before I got my grubby paws on the bike. I was relieved as I really didnt want to mess with valve clearances, and focussed on dealing with the intake issue.


:blah

.05mm increments are pretty close to standard (or are at least consistent with the gauge sets I have), and the method you described sounds pretty much dead on correct procedure. does sound like you have one intake valve that needs adjusting. yours is a 4-valver, yes?

[98lee]

I must make another embarassing crawl into a crack here. All I had was a feeler gauge in .05mm increments (and an imperial ignition gauge with thick blades) - so it was a 'go/no go' type deal. All the exhausts would take a .25 but not the .30, the inlets took the 0.15 but not the 0.20, except one which was greater but would not take the 0.25. I set out to do a careful measurement of the valve clearances, but had to back off when I took a look at my feeler gauge. I was left with the impression that the valve clearances had been carefully adjusted before I got my grubby paws on the bike. I was relieved as I really didnt want to mess with valve clearances, and focussed on dealing with the intake issue.


:blah

Those are all fine.

They are all in spec., except for the one intake, which would cause no problem except for an inperceivable lose in horsepower (due to the lose of lift on that valve).

The exhaust is MUCH more critical because:

1. the exhaust valve gets cooled by seat time as opposed to the cool inflow of the air fuel mixture (like the intake valve)

2. the exhaust valve tends to tighten up over time (valve recession)

3. normal operating temprature in the exhaust causes expansion that reduces the clearance ( that's why you have lash or clearance when cold) and that's why they have to be checked cold.

4. if the clearance ever gets so tight that, during operation, the valve doesn't seat well, you will loose a great amount of power and run a great risk of burning that valve

I would not be concerned at the moment. You can change the shim now or wait and see if it has changed the next time you check the valves.

Congrats on finding the problem. I was a little misled when you had said that you had checked for cracks in the manifold tubes. Plus I usually try to check the things that are easiest to check first or need to be checked anyway (basic first).

Although, while reviving one of my bikes that was a salvage recovery, I was chasing an extremely lean condition and figured after eliminating almost everything else, that it had to be cracked manifold rubbers. So I changed them all. No change.

THEN I checked the valve adjustment!:doh

That was it. The vacuum was higher, the power and mileage dramatically increased, the motor turned electric motor smooth and that annoying rattle just off of idle disappeared.

It took WAY less TIME and MONEY to do the valves than it took to do the intake rubbers. Oh well, Live and Learn (I keep living, I hope one of these days I'll learn)


:dance :dance :dance

[rmarkr]

The irony of this situation is that a leaking manifold rubber cost me dearly in an offroad race that I was leading. It was a SWM 360 (not a common bike) and the inlet tube got hot, soft and let air in behind the carb, and sure enough the bike seized up. It was difficult to diagnose because by the time you got to take a good look at the bike, the rubber was firm again. I vowed it wouldnt happen again to me - and look at this. Thankfully, no engine damage (I hope). Furtively, I did put a light into the spark plug hole to look for a burnt piston - it had to be unlikely.

What did cost me though, is a dropped valve on the Guzzi, about a year ago. I had just done a full on head job with new valves, guides, the works - the bike was purring. I got caught in a heavy downpour and one pot stopped firing, so I stopped under a bridge to dry it all out, including the points (old bike). I must have upset the gap, and hence the timing, and in a fraction a second the engine was trashed. I could have wept. My guess is that the exhaust valve got hot, soft and let go.

Here's the damage

11494

[rmarkr]

11526

All went well. The bike is idling smoothly and the gentle knocking from the rear of the engine is gone. I have not taken it for a ride - its cold and wet out there.

A few notes on the repair. I suspect that more of the older bikes will suffer this malady judging by the fatigue of the rubber manifold bushes - they were all about to fail.

WARNING!!! There is a clear and present danger that dirt and small parts will fall into the intake manifold or ports. Clean the engine first, have a vacuum cleaner handy and be careful. Ingesting a nut or bolt could spoil your whole day!

To get the TB assembly out all the crimp-on (oetiker clamps - thanks Don) will need to be cut off (they cannot be reused). I was able to find a few from Bob's and surprisingly Napa had an adjustable clamp (see next post). There are 8 in total. Reattaching them was easy - using a pair of end cutting pliers.

The replacement parts I fitted are:
New rubber intake bushes
New O rings under the manifold tubes (injector housing)
New O rings to both ends of the injectors
All the hose clamps - 8 oetiker clamps and 4 screw-up (no pun intended) clamps

I found that my throttle position switch does not make the "click" as is described. What I did is, with the engine running with a very small throttle opening, I rotated the switch to clear up the hesitancy and surging. I sounds good in the garage.

Thanks once again for the knowledgeable advice, and it was great to have the problem fixed. Itching to ride!

I will fiddle with my new toy until the weather improves - a Nolan N-com helmet with BTooth.

[rmarkr]

11527

These clamps are too narrow to be substituted for a srew-up type. They are easy to apply, and by the way, they can be tightened up at a later date with another squeeze of the pliers.

[deilenberger]

Mark..

Looks good. One thing - your TPS (throttle position switch) doesn't click. Instead of being a switch - it should be called a throttle-position-sensor. It's actually a potentiometer that tells the ECU how much fuel to send the engine. Setting it requires an Ohmmeter and the spec's which I don't have offhand..

The Oetiker clamp pliers are made to tighten the clamps to a set pressure.. which keeps from squeezing the rubber under it too hard. As long as you didn't pull your end-cutting nippers as hard as you can - you're probably good to go with those.

Hope it warms up enough so you can do a test ride!