Anybody else have a problem with run-on/dieseling  By  indymoped (Read 337 times)

Too lean of a engine will cause it to overheat. Check your airfilter intake boot and intake manifold closely. You very likely have a crack or cracks that are letting air leak into the system causing the engine to run too lean. This is the most common ailments with the 150cc scooter engines. That rubber intake manifold tends to dry out fast and start cracking and leaking. The large air filter box rubber boot also tends to have that problem too. I have had the rubber boot between the air filter box and the carb come loose and it caused the engine to not be able to go faster than 25mph then.

You might want to go one or two sizes larger on the jet in the carburetor as they tend to be set very lean like that from the factory too, right on the thin razor's edge of being too lean. Thus it takes very little for something to cause it to be too lean.

Another thought is the PAIR system may be leaking and causing it to to be a bit too lean. But it isn't the pair system per se, as much as the vacuum lines going everywhere can develop an airleak. If the PAIR system valve fails the rubber hoses burn up pretty quickly.

The carb diaphragm for the CV slide valve can sometimes be a problem if it develops a small tiny pinhole or tear in in.

If you haven't done it also check the valve gaps to make sure they are OK, if the valve gaps close up, the engine starts doing funky things like stalling out at stop lights or stop signs as you slow down, not wanting to idle good, etc.

Now then one needs to be careful with a new engine, they run more hot at first until they get broke in and run in real good. If it is hot outside and you are riding around at or near full throttle all the time, the engine does get real hot like that. But normally dieseling went out of style with the old automobile engines and their crappy mechanical emissions systems of that era years ago. The computer controlled systems they use today don't have that problem.