1990 yamaha 150. was running great and halfway through the day the motor now is 1) sluggish to plane, 2) will top out at 4000rpms and then drops to 3400rpms after a few seconds. it starts and idles and puts around great but its like it drops a cylinder at high rpms.
initially i thought it was fuel related so i rebuilt the carbs, replaced both fuel pumps, replaced spark plugs, have changed all filters, have run off separate fuel and fuel tanks, ran fuel directly to the carbs, compression is great and i have spark at idle but cant run a WOT test. it will run at 3400 all day but as soon as i get to 4000 it drops back down and is generally weak. any ideas? thanks.
initially i thought it was fuel related so i rebuilt the carbs, replaced both fuel pumps, replaced spark plugs, have changed all filters, have run off separate fuel and fuel tanks, ran fuel directly to the carbs, compression is great and i have spark at idle but cant run a WOT test. it will run at 3400 all day but as soon as i get to 4000 it drops back down and is generally weak. any ideas? thanks.