I have spent alot of money and time trying to get this motor back to running normal. Here is the situation, any help is greatly appreciated. This is a 4 stroke 60HP Yamaha High Thrust.
idle to about 3500RPM motor is hesitating and popping in the intake. At idle motor will shake your teeth out. Weird thing is at high RPM motor runs fine. I think initial cause of this was at one point i left gas in motor sit to long.
What I have done:
- had a local shop rebuild all 4 carbs. Spent $900 but motor ran just like it did before i took it in. Not sure if they actually did anything.
- pulled head, had it reworked and checked. Head was resurfaced, new gasket, set valve lash to spec, etc.
- Rebuilt all 4 carbs multiple times
- New fuel line
- new spark plugs
- tried re-syncing carbs but bottom carb wont sync
- leak down test is fine on all cylinders
- pull plug wire on bottom carb and no affect to motor
- pretty much seems bottum carb is not firing at low rpm
- new coil packs
My guess is the bottom carb needs replacing but it has been rebuilt multiple times.
Here is a video of the motor running and vacuum gauge on each cylinder/carb: Motor Run Video