Re: Yamaha 25HP 2 stroke misfiring
I can only think of three immediate possibilities, SPARK, GAS, FUEL TANK VACCUM. Since you say you had the carbs done and the engine completely serviced, your problem sounds like a coil going bad. A bad coil will still let you run at lower RPM's and give you trouble at higher RPMS's. When this type of problem is present, it's usually heat that causes the coil to break-down and malfunction. If this is a heat related problem, Ohming out the coil may not do you any good. Try pulling the plugs to see if one is more fouled then the other. If So, you might try swapping your coils and see if the condition of the plugs reverse. Without know what model or year your engine is, it's hard to tell. All fuel tanks need a vent so when gas is removed, air can take it's place. Without proper venting, the fuel tank can develop a vacuum and starve the engine for gas at higher RPM's (greater fuel demand).
