Hello, This is my last resort for help on my bikes issue. I hope your experience as a group may come up with a solution.

I have a 1987 K100 RT 2 valve motor.

Bike had sat under cover on a trailer for at least 4 maybe 5 years with intermitent running.
I was given the bike by a really cool neighbor and spent 1 1/2 years restoring it to on road/ safe condition. I have been riding it for a few months now with the original owner riding by me on his Harley. The last few rides I have been having an issue with the engine running eradically at slow speeds under load. While in town I tried to maintain the 25MPH speed limit and the throtle could not keep constant. It acts like it cannot make up it mind on too much or too little. As soon as you pull the clutch in it it stops acting eradic. It does not stall but if you down shift or up shift it still does it in those three gears anywhere from 2000 to 3500 RPM. The bike still goes but it sounds like the metal trap door on the air inlet is going nuts slapping open and closed constantly. The bike seems to run great in 4th and 5th gear just fine, No problems downshifting either.

Things I have replaced or fixed:
Fuel filter ( BMW and in correct manner)
Fuel lines on the entire bike in tank and out (correct ones for each)
Air filter
Plugs NGK (the BMW Bosch plugs fouled early on and the bike would not even start) replaced with the correct NGK and the bike had run fine till now. By the way took the plugs out and they all look normal.
Crank case breather hose is new.
all the vacumn nipples and hose on the throttle body end is new.
New tires, brake pads/brake fluid
new engine oil
new trans oil
new final drive seal and oil

I just bought new plugs to try
I unplugged the Throttle position sensor last night and ran the bike on centerstand and held throttle at constant 3000RPM. It still had trouble keeping a constant RPM even in neutral so i think I eliminated that as an issue.

I have not replaced the spark plug wires or coils.
I have not replaced the fuel pressure regulator
I have not replaced the fuel injectors

I do not know but I speculate that this is a electrical or vacumn problem. I am hoping someone out there may have had a similar problem can may have a solution I can try. The bike is great and I enjoy riding it but I know it is not runnning correctly. I have put a lot of time and money in this bike and want to get it running as well as possible. Any ideas or help is greatly appreciated.

James

It sounds like an air leak.
Have you looked at the intake manifold (rubber intake connection between the throttle body and the engine)?
The easiest way to check it, is to start your engine and use a propane torch.
You DON'T ignite the torch but just blow propane around the rubber intake connections. If the engine RPM goes up, this reflects a crack on the rubber. This is a 'common' problem on a 20+ years old bike. The rubber dries up and cracks.
Caution: Any time I am working with flammable material I always have an extinguisher ready to be used. With this procedure, the risk of fire is inexistent to very low but just be prepared for any unexpected event,
Let us know your finding.

Bert

I will absolutely second the motion to have a fire extinguisher handy (ask me how I know - and still have a K).

Sounds all too familiar, It took me 4 years to figure out and fix mine. The flaping may be the air/fuel sensor. It's bad if it's flaps around--it's supposed to be spring loaded. I also replaced the wires and coils and then the bike problems went away. "Now" I have and bike that is awesome to ride again.

You mention plug leads, but don't say if you have changed them?

I've come across several folk who have eventually traced a mis down to the leads - AFTER changing everything else !

Leads are one item that seems to get overlooked in the routine annual maintainence scheme.

I will attempt to try each of these and will let you know what I find as the culprit. Another K bike owner suggested using starter fluid around the throttle body area. I do not have a propane torch. Would starter fluid work the same. Thought I would ask before I try with Fire Extinguisher on standby. I have not replaced the spark plug wires or coils yet. I believe that is what you were refering to. Is there a way to test the coils other than running the bike in the dark and looking for a spark? Would the airflow meter(This is located in the Air filter box correct?) flap uncontrolably at lower speeds due to a spark plug or coil issue? If anyone else has had a similar problem and had fixed it please let me know. Again, Thank you fellow K bike owners for the help in tracking down this issue. James

Starter fluid is a bit too flammable for that function for me. Do you have any carb cleaner? You can use that to spray around the boots to detect air leaks, but really, do yourself the favor and have a fire extinguisher right beside you. I had a little raw gas spilled at the injectors and I think the vapors ignited from the alternator spinning/arcing as it did it's job. Without the extinguisher right beside me the bike would have gone up for sure, taking the garage and attached house with it.

The usual garage standby is a squeezy bottle with some washing up liquid and water - totally non-flamable and cleans as it goes !!! Works for outward leaks as well [ small ] as you then get a bubble formed where the leak is.

Would washing up liquid and water be more appropriate to detect leaks in a hose under pressure? Could you see the bubbles 'exploding' if the soapy solution is sucked into the boot? I never tried it on the boots and don't deny that it may work.

The boots between the head and the throttle body are under a depression.
The goal of using the torch is to have the engine sucking the propane through the crack which will create an excess of combustible material in the chamber and should be reflected by an increase of the idle.

The theory is that the liquified gas temporarily "seals" any inward leaks - washing up liquid / water does exactly the same thing - been using it for the past 45 years or so! When used in that mode the engine will settle momentarily indicating you have found the leak. It's quite precise - we found a pin hole in my pal's Volvo emission system using this method - curing an annoying miss that he'd had for months. Also a faulty intake gasket on another pal's Renualt Espace.

And conversely when there is an escape of pressure - a bubble will form. Only low pressure obviously.

Starter fluid is not really a good idea, standby fire extinguisher or not !

126,000 on 85 K100RS
I'd check valve clearances, easy to check, hard to adjust. Mine was rough below 3000RPM, esp first 5 minutes, with 7 of 8 valves too tight, esp exhaust.

I'd invest in Stabilant 22, NAPA CE-1, a $70 ear dropper full of "contact enhancer" dab a drip on each blade and female computer connection under seat, F1, other places good to get are under tank and both blades on each fuel injector.

The Caig labs DeoxIT is way lower cost than Stabilant is made in the USA and widely available. Many consider it superior. http://www.caig.com/
Regards,
K-BIKE

Hello all, This is long overdue. I forgot to post a reply and follow up about this. I appreciated all the advice. I tried the cheapest thing first and it seems new spark plugs may have done the trick. Thank you all again. James

K-bike, is the deoxit any better than the CRC precision contact cleaner?

Hi geordnz,
My belief is yes, I didn't find the CRC very effective at fixing cell phone problems where DeoxIT was an instant fix. I was also staggered by how when I cleaned the pins on my ABS & Motronic with DeoxIT which I had previously treated with contact cleaner (Electrolube which was much touted in the UK when I lived there) the amount of black stuff which came off after the Deoxit treatment absolutely staggered me. I had previously sprayed with aerosol contact cleaning solvent to remove all loose stuff and previous Electrolube.

After using the DeoxIT cleaner I used the DeoxIT Shield and then have progressively gone through every connection on the bike. Jaycar stock the two bottles of the Cleaner but you will need to chase around for the aerosols of the Shield. I got mine at Ron Enright Tools in Ellerslie about $30 for the aerosol from memory. The mini aerosols from Jaycar are a WOFTAM as they are too small.
Regards,
K-BIKE