'88 k100LT,70k--bogs, surges, etc., after heavy rain

[Tighthead]

I posted this over on k-bikes.com earlier, and someone suggested that I might get better information here. Thanks for any assistance you can offer.

My story:
Bought an '88 k100LT with 69k miles a few weeks ago. It ran wonderfully with great power, acceleration, starting, etc. Last week I rode it from Harrisburg, PA to Montreal for work. On the way up, riding through the Adirondacks on rt 87, I fell in love--what a nice bike!

On the way back (last Thursday), I rode through heavy winds & rain, including a torrential downpour around Lake George. The kind of rain that turns the seat into a bathtub. Around this time, the instrument panel started acting up--the gear indicator and neutral light, primarily. I chalked this up to the rain and didn't worry about it too much.

I had to stop for both gas and other sundries and the bike sat and got absolutely soaked for about 5 minutes. I forged ahead and the bike developed a noticeable lack of power--I held the throttle wide open and managed only (an indicated) 80mph and 5000 rpm. I rode the rest of the way home like this. On the back roads from the highway to my house, I noticed it would bog and surge around 2000 rpm, then continue to hesitate and just not run very well. I had no problem with starting or idling.

The bike's been sitting in the garage since last Thursday night, completely dry. The instrument panel is behaving, and the bike starts immediately and idles a little rough but not too bad.

The bike still exhibits the same behavior when I open the throttle. When I open the throttle quickly, it hesitates, makes some rattles/clunks, then the rpm increases. It's really in the moment that the throttle opens when it sounds (and feels) the worst. I can feel the rattle/clunk in the handgrip. It is pretty rough. When I roll on the throttle slowly and smoothly, it seems to like that much better. I took it for a short test ride and it really bogs and hesitates under a load. So much so that I don't feel comfortable riding it.

I had already purchased plugs and a fuel filter, intending to change these out at some point. 2 of the 4 plugs I pulled had dry carbon deposits, but not really all that bad (they were just black). The other two looked very good. The wires looked fine so I re-used them. I replaced all 4 plugs and noticed no change at all. I pulled the side panels off and cleaned every connector I could reach, and unplugged and plugged the big ECU connector. I cleaned the ground coming from the battery & coils. None of these really looked bad at all.

I replaced the fuel filter, and noticed no change at all. I pulled the cover off of the HES and the gasket looked in pretty good shape--flexible and not cracked. I have not pulled the tank off yet.

I'm pretty far from a mechanic, so I'm not sure where to go from here. This definitely seems like something acute rather than chronic, as it really just popped up from nowhere, and only once the bike was ridden through heavy rain. But I'm not sure if that's really the cause.

Should I look at the coils more closely, or the air filter? Any other thoughts or suggestions? Am I missing something obvious?

Many thanks--I know you guys get these questions a lot, but if I end up getting things back to normal, I'll certainly be sure to post the solution.

[wmax351]

Check the old plugs. Should let you know if there is too much fuel/no spark or if there is too little fuel.

Check the wiring on the injectors, coils, spark plugs, etc. Remove, WD-40, and dielectric grease all of the connections.

Also check the Air intake for holes that could suck in water. Shouldn't be an issue. A hot engine ingesting small amounts of water is harmless (its how you de-coke older engines).

[mystic red]

Yea, I suggest that the rain had nothing to do with it, just coincidence.
You might have an air leak in your intakes. That's kinda what mine was doing. Look at this thread.

[johnny]

greetings tighthead...

welcome to motobrick.com...

the moes here will get your motobrick sorted out...

j o

[Rick G]

I agree with Mystic Red and also remove the plug on the ECU under the seat and make sure it is dry also the CDI unit which id right behind the steering head under the top frame rail and make sure it is dry as well. I have had water in both of those and it caused problems.
The gear indicator problem is also caused by water in the switch which is on the back of the gearbox behind the swingarm. If it is working OK now leave it alone but it will most likely give you more trouble and you will need to water proof it with some silicone or similar.
Glad you like the brick they are a mighty good wagon.

[Chaos]

The rain might have been a red herring.  Check you crankcase breather hose for cracks, it can lean out the mixture if leaking air causing hesitation.  Appox 3" S-shaped rubber hose to the rear of #4 throttle body.   Buy a new one here: http://www.beemerboneyard.com/11151460480.html

[frankenduck]

I agree with Mystic Red and also remove the plug on the ECU under the seat and make sure it is dry also the CDI unit which id right behind the steering head under the top frame rail and make sure it is dry as well. I have had water in both of those and it caused problems.
The gear indicator problem is also caused by water in the switch which is on the back of the gearbox behind the swingarm. If it is working OK now leave it alone but it will most likely give you more trouble and you will need to water proof it with some silicone or similar.
Glad you like the brick they are a mighty good wagon.

Wow. You got water in the ICU connector?  :o You're not supposed to submerge K bikes you know.  ;D

[Rick G]

I agree with Mystic Red and also remove the plug on the ECU under the seat and make sure it is dry also the CDI unit which id right behind the steering head under the top frame rail and make sure it is dry as well. I have had water in both of those and it caused problems.
The gear indicator problem is also caused by water in the switch which is on the back of the gearbox behind the swingarm. If it is working OK now leave it alone but it will most likely give you more trouble and you will need to water proof it with some silicone or similar.
Glad you like the brick they are a mighty good wagon.

Wow. You got water in the ICU connector?  :o You're not supposed to submerge K bikes you know.  ;D

We did get 14 inches of rain in 3 days and I had to ride through near 15 inches of water on 2 occasions. Had lots of fun till it started playing up.

[Tighthead]

Sorry for the delay in updating this--I appreciate the suggestions so far. I have not been home more than a couple days over the past few weeks, so I my time's a bit limited. So I haven't tried all of the suggestions--I did not look at the crankcase breather hose, for instance.

I checked the spark plug leads with a spark indicator (the kind you press on the lead and it glows showing spark), and it seemed to me that the indicator showed weaker spark on the wires attached to the left coil, especially at rpms where I have trouble (starting at 2500--3000).

I took the coil pack off and test it with a multimeter. The resistance of the high-tension leads look dead-on, at around 12.6kohms (I have an analog multimeter, adjusted correctly), and both are exactly the same ('dead-on' based on a k100 EFI troubleshooting guide I found online).

The document I found on the web says that the resistance at the primary coil should be 'about' 2.6ohms. Both of mine look like they're right at 2.0. Obviously not the same as in the doc, but both were exactly the same.

So, while the spark indicator appeared to show weaker spark, the resistance measurements appear to be identical for both coils.

I suppose the spark plug wires are next to check? Any other suggestions? Thanks!

[johnny]

fuel pump connector... under the seat and under the tank...

j o

[wmax351]

Could be cracked coils. They develop micro-cracks, and voltage will leak out of them. You should be able to see it in the dark. The problem is exacerbated when it is wet. Either replace the coil, or dry it out really well and coat with JB weld. I had it happen on my Jetta VR6. Used a coil pack, and it would stumble when wet. Soaked it in JB weld, and its good as new.

[kennybobby]

+1 on the micro-cracks in the left coil. 

Another way to test for leaking coil voltage is to put some spark plugs into those cylinders with an extra small gap, say  ~ 0.010" and see if the problem goes away.  This is just a temporary setup to check for weak coil voltage--the smaller gap takes less voltage to fire.

[mystic red]

I still smell an air leak.........get the propane out and fish around the intakes just to rule it out and make me happy.

[Tighthead]

Sorry for the long delay.

I think I found the issue. Today I picked up some starter fluid. I used the friction screw on the bar to hold the rpm at around 2k. I sprayed a generous bit of started fluid in around the intakes and the rpm increased to around 3.5k, then after a bit came back down. I repeated this 3 or 4 times, and it works like a charm every time.

Thanks to all for your help--I'll post here again once I've completed repairs and verify the fix worked.

[mystic red]

Sorry for the long delay.

I think I found the issue. Today I picked up some starter fluid. I used the friction screw on the bar to hold the rpm at around 2k. I sprayed a generous bit of started fluid in around the intakes and the rpm increased to around 3.5k, then after a bit came back down. I repeated this 3 or 4 times, and it works like a charm every time.

Thanks to all for your help--I'll post here again once I've completed repairs and verify the fix worked.

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