Nope lied again Bike rode fine this morning after sitting all night in 60 70...

netboard

Nope, lied again. Bike rode fine this morning, after sitting all night in 60-70° weather, after sitting in the 90° Sun it ran like crap again..almost certain it's compression.

%d comments
  • Engine combustion temp is much higher than ambient temps, so probably not compression.

  • The coils have been eliminated as a probable source since I swapped coils and still had trouble with same cylinder

  • Weird. Still would not think it's compression, unless the problem comes on as and after the engine is warming/warmed up. Even then I'd look for some external problem. Have you tried swapping the spark plugs and or spark plug wires side to side?

  • Yeah, tried plugs, wires, points, carbs, battery..I've been chasing the problem for a few days now

  • So just to be sure, it only does this on hotter days? And when it does, you loose a cylinder? And when it does it still has spark? If it still has spark, then yes. Something not electrical for sure. Then I'd start with a compression test when it has the problem.

  • That would be correct. During the early morning, and at night the bike rides fine. During the afternoon the bike is on one cylinder

  • Next time it does it, try the choke or enrichener. Might rule out fuel too.

  • Haha, I'm sure it will turn out to be something completely dumb, that was just too simple to think of.

  • There are a few things I can think of but they are pretty "out there". First, if the valve lash is set so that there is litttle or no gap when the engine is real hot the bits expand just enough to lift a valve off its seat. Second, an electrical bad connection which manifests itself when the joints get hot and expand or the air is less moist.

    I used to be fascinated years ago that my bike ran dead smooth when going home on an evening. If there was a fog it ran best of all. Eeerily so. Its because a little moisture helps combustion. Perhaps your bike is out of tune but the dry air during the day is the final straw. Don't forget a lot of small errors can add up to a badly running bike making diagnosing difficult. I sure hope you fix it.

  • Check the air cleaners