Will Not Run When Warm

I am stopping short of saying it is a coil problem. If it.is.only on one cylinder, I would say it COULD be a coil, plug wire, spark plug. All the secondary ignition [high voltage] pieces. If it is on BOTH cvlinders I would more suspect primary ignition [all the low voltage pieces]. I may be wrong. Hard to diagnose from half way around the world ...J.D.

 

Hi
I had almost exactly the same issue with my 78 140V. After replacing the coils,leads and plugs i eventually found rhe problem. Check the temperature of each carb when the bike warms up, they should be cool and not hot. You should have heat resistant spacers between the carbs and the inlets manifold. If they are missing the heat dissaptes into the carbs, the petrol then evaporates and causes the engine to miss and run unevenly. Is it difficult to start when the engine is warm ? Mine was a mare until i replaced these gaskets now it runs great.

 

The choke can hide clogged jets at startup. It's because when cold the engine is running rich under the choke. Once warmed up, the choke disengages and the carb jets have to do the work. If they are clogged, you are going to run lean and will have some spots on the throttle where it can just die from fuel starvation. My old bike would often get a clogged idle jet, so it wouldn't idle. Other times the main jet would be clogged and the engine would bog at half throttle and die.

 

Running with the choke on can hide a lot of things. The rich mixture makes it easier for the fuel to ignite. That is until it gets TOO rich. Running on choke can also cover up a vacuum leak, or a weak spark at times. I recently had the opportunity to diagnose a problem on my rototiller. I had loaned it to my son. When I got it back he said the carb was plugged up and he had cleaned it out. NOW it would run OK until it warmed up. Then you would have to choke it.to keep it running. I found my son had failed to install the gasket between the carburetor and the head. As I said, rich mixture hides a mulitude for problems. ...J.D.