Originally Posted by davis
I am in the south east, thanks for the advice MOS , stripped the carb again today cleaned and blew it out , changed the oil , put back together and it started and ran for a while then I turned it off. Tried to start again and no go so maybe what you are saying may be the problem , but the engine is not in warranty anymore so probably no hope of a new carb from them. I was going to try the fuel line and pump next to see if there is any dirt in there ,other than that I dont know , but the fact that it started and run it must be a fuel problem.
These engines are not easy to get at everything seems to be packed in around each other.
OK, It does sound like the issue is the carburetor. The dealer you should have bought it from should help as it is a known Yamaha fault... Even out of warranty. We used to just change the complete carb for a new one and it did solve running issues. I have also known people to drill the main jet out slightly which improves the engines performance as it allows for fuel to mix with the air.
Also, try this:
Try putting a brand new BR6HS NGK plug in.
Remove carb again, completly strip it down including top heat shield with white plastic dowel. Allow the carb to be submerged in fresh petrol for a good 24 hours. Then blow out with a 100PSI + Air line...
Thirdly, reset the pilot screw... Some F4 carbs allow you to change the pilot screw but others (newer models) had blanking plates so you couldn't. If yours is not blanked off then you will need to create a special tool (half mooned screw driver) to screw the pilot out 1.5/8 turns +/- 1/4 ...
Hope this helps