1985 Yamaha 4 HP races on start up - can't control

fishon71 · #1 July 15th, 2008, 09:22 PM

2 stroke Yamaha 4 hp, starts right up and races to full throttle. Throttle cable disconnected and carb butterfly closed all the way. If I choke it completly the rpms will come down. Also smoking like crazy. Seems to be sucking air from some place, any ideas ???

DadTo2Marines · #2 July 16th, 2008, 05:15 AM

torn gasket at the carb or intake. I would use pull both and replace each gasket.

fishon71 · #3 July 17th, 2008, 11:21 AM

Okay solved sucking air problem, you led me right to the spot. Previous owner mounted carb with lock washer in between carb & gasket. Now motor start runs well but I can’t get to idle. Every time the RPM’s drop to idle motor want to die. If I choke slightly and give it gas it comes right back. Iv’e been messing with the mixture screw but really don’t know where to start and not sure if there is another problem. I cleaned tank, put in fresh gas and took carb apart soaked and blew everything out. I look forward to you suggestions.