I have a 2006 Yamaha F6 4 stroke engine. The engine will start first time, first pull. Thereafter, once warm/hot it is unlikely/impossible to re-start. I have cleaned carb and coolling which improved re-starting but still totally unreliable for a guaranteed hot re-start. Any suggestions?
I used to have the same problem with 4 stroke off road motorcycles, generally after being dropped. Some possibilities:
1.Marginal pick up or ignition coils or plug that start to break down with heat
2.Float level too low or high. Try shutting off the fuel at re-start. If it finally fires it may be being flodded.
3. Float that is leaking, causing over rich condition which may allow cold start
but not on hot re-start.
4. Check all hoses and connections for air leaks. Hoses close to the block may develop cracks from the heat.
5. Check for debris in any air bleed jets in carb, possibly causing an over rich condition when hot
6. Make sure carb is tightly bolted to the manifold flange.
7. A stretch, but make sure the valve clearances are set properly. Perhaps try the above items first.
Let us know what you find.