Yamaha 1986 PROVJ 150 HP- cuts out at hi speed

MGA

Cadet
Joined
Jun 21, 2007
Messages
17
The engine runs great - but at full bore after about 5 minutes I feel like I am losing one cylinder - drops a 100 rpm or so them catchs back then drops. you can't really feel it but you can hear it and see it on the tach. It runs all day at 3000 rpm.

I have cleaned the gas tank, put in a fuel water seperator and a filter, new fuel pumps, cleaned carbs, I don't think it is the fuel systems.

I just replaced the plugs, the top starboard plug top screw on part along with the connector were corroded, cleaned the inside as best I could with steel wool on the end of a drill bit and replaced.

I am temped to replace plug wires, next but I still don't know what the problem is I am just blindly trying stuff
 
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