Hey all,
Here's a challenge for the best of you...The problem I am having is that the bike will run great for a while and then randomly start loosing power. It sounds like it is only running on one cylinder but there is no backfiring, fuel dump or anything to indicate that. The bike doesn't immediately die and none of the warning lights come on it simply begins to run out of power. I can continue to ride it for a couple of minutes while the power drops out but at some point it finally will stop. It will run at idle but very rough. If I let it set for about 10 minutes it will fire up again and will either run a little ragged (like the timing is off) or run fine. That too is random. If I let it set for a couple of hours (4 or 5) it starts and runs like it never had a problem. It is irregardless of bike temperature, air temperature or riding type (cruising or throttle on/off). I cannot duplicate the problem when the bike sits running in my garage and it usually takes at least 5 miles (sometimes more) before the problem shows up (if it does). I have checked all of my electrical connections and grounds to make sure and they are all good. To make it even more baffling all of my electrical components are Magneti Marelli including my coils so my electronics do not look like the stuff I've seen from other posts or in the manual. Because it happens randomly when I ride I haven't been able to strip the bike at the side of the road and check fuel flow or vacuum into the carbs (dual dellortos) or anything electrical. The only thing I have confirmed when it happens is that the fuel pump is working and the fuel circulates back into the tank through the return line and I have full electrical (gauges, lights, etc.). According to a local shop that knows the Dellortos they said everything is jetted right and they can find nothing wrong with the fuel delivery because the bike won't misbehave for them either. Any ideas? I might have to put a steak dinner on the line for the person who can solve this!

I know you say the problem occurs regardless of bike temperature, but I think the trouble may be tappet clearances. Four or five hours is the kind of time it would take a tight tappet to cool down sufficiently to let a valve close if the tappet has been running too tight.

It can be difficult to estimate what temperature the valve gear has reached. You could let the bike sit at a fast idle and see the gauge reach 100 degrees, but the valve gear could well still be cooler than if you had been riding for an hour with the gauge never going over 80 degrees. This is because it takes time for the mass of the valve gear to heat up.

The only time you can be sure of valve gear temperature is when the bike has been sitting overnight - which is why the manual says to let it do that before adjusting the tappets.

Hmmmm - maybe Skins - is worth checking, but it probably be something simplier - how about checking the vent for the fuel-tank is'nt blocked...................

I wish I could help but i don't have a clue, (no steak Dinner for me ) It is interesting though to see another Paso / K100RS owner. There seems to be a few of us out there

I know the vent is not clogged because that was one of my first inclinations from earlier postings. The tappet issue sound interesting. If I understand what you are saying it sounds like I may have a valve that is sticking? I don't see how that could happen on a desmotronic valve system without creating permenant damage.

Speaking from experience, while the desmodromic architecture greatly eliminates any ambiguities in the valve system, it is not impervious to defect. If you had a valve that was sticking, you'd know it, that doesn't mean their timing can't be unaffected. At the very least, the half-rings that sit in the valve stem and hold the closing shims in place can cause the valve stem itself to disform and 'mushroom' above the half-ring - this happens due to the high temperatues and the force of the closing rocker pulling the valve shut. This happened to a small degree on my Monster, when I replaced the half-rings with MBP's collets. (I wound up covering up the service opening, suppressing the closing rocker and sanding down the valve above the notch for the half-ring in order for the closing shim to be removed.)

Otherwise, you're right - too much free play in the valve system will cause permanent - or rather, expensive -damage.

But I'd think any changes in the valve system sufficient enough to create combustion problems only after things are hotted up would cause trouble right off the bat. I'd think you'd only notice a deterioration in performance over a span of months, not hours, and certainly not getting any better.

Another thing to check might be the exhaust headers and collars, which hold the pipes to the manifold. How about your belts - how many miles on them? Are they tensioned properly? Actually - how many miles do you have on the bike? Also, back on the topic of the valve service ... how does your carb and the airbox look? Any oily residue up in there? Have you tried R&Ring the carb, checking the valve settings, etc?

No, the valve isn't sticking. This is what might be happening:

The cold setting clearance on the opening shim is supposed to be 0.1mm (about 4 thousands of an inch). When things get hot and expand this clearance will reduce to running clearances, which will be close to, but not quite zero.

If the cold clearance is out, say 2 thou instead of 4 thou, when things get hot and expand, all the clearance and then some will be taken up, and the rocker will be in constant contact with the valve stem, preventing it from closing properly, so you lose compression and proper combustion. There should be no damage, because the valve is still nowhere near hitting the piston, and without proper combustion, things won't be getting too hot inside the head.

Of course the constant contact between rocker, shim, and valve stem will generate heat and wear in that area, which should be looked at closely.

Remove the fairings - ride it till it plays up - then check for spark getting to both cylinders. Could be a coil breaking down under load/heat.........

I would focus my attention on the fuel system and delivery. It sounds like you have a fuel pump AND Dellortos. You do not need a fuel pump with these carbs. They sit below the fuel tap and really only need gravity ( I have them on my 750, no pump) feed to make them work. I would find a way to disconnect the fuel pump or eliminate it and see if that solves the problem.

When this problem happens, have you ever pulled the plugs to see what they look like??

Have you checked for spark when this happens?

Was the bike running fine and then this problem cropped up after some work had been done?

Let us know what you find.

Something else worth thinking about - is the voltage regulator playing up?? If this is sending power-spikes/overcharge into the ignition system - this will create these symtons sometimes. Bike stops - regulator cools down & reverts to 'normal' - then plays up once it gets hot again.........

Hey everyone many thanks for the tips. I just finished the 90,000 mile tune up and go through on the BMW so now I have the time and space to dig into the Paso. But, I have a couple of quick questions before I begin my quest for the answer.
1) What is the best way to check spark? Previous posts have mentioned how bad it is to disconnect the plug lead while the engine is running. I heard that someone makes an LED indicator that you can wrap around your plug wire and it blinks to confirm spark. Anyone else heard about this?
2) Any ideas how to test the voltage regulator until the problem surfaces? If not I'll just have to spend a day riding around until it happens (come to think of it that's not all bad).
3) After I exhaust these ideas I will check shims, belt tensions, etc. The bike was in for a tune up about 1500 miles ago so I hope not to find a problem there.
4) In regards to not using the fuel pump...I assume the carb inputs need to be below the petcock for that to work? Being the retentive person that I am I do not want to run the fuel lines across the top of the engine or between the cylinders so I ran the fuel line along the frame up to the crown then split it and ran it back to the carbs along the frame rails. Because of this added distance I think I may still need the fuel pump.