motor losing rpm

[bondjeffrey]

any suggestions on what would cause a motor to act like it is losing rpm's while at full throttle, but you can let off the throttle and get back on it and it may run fine the rest of the day or it may act up the whole day. At first i was thinking it was a carb issue, but have went through them twice already, any suggestions PLEASE!!!!!SORRY this is a 40 hp yamaha 2-stroke.

[99yam40]

what motor are you talking about?

Spark, too much fuel, or too little fuel are all possibilities.

plugs, plug caps or wires
you can test to see if dropping spark with a induction timing light maybe by hooking it up to the different plug wires
Change plugs test caps and wire and coils like manual says

check fuel system pressure and vacuum and see if it is sucking air or restricted, maybe bad fuel pump

My C40 had jets someone drilled out that caused high speed miss had to replace them to fix