unsteady speed

[flyingscot]

I need help ! This one's got me baffled. I bought<br />an older Wellcraft boat in the spring equipped with a 1987 Yamaha 200 HP , model 200ETXH, ser.#<br />7176A787. The motor starts very easily. Up to<br />about 2800 rpm it runs great. Then things start<br />to happen. Above 2800 rpm and up to about 4000 rpm<br />the engine rpm's fluctuate very slightly, not even<br />enough to affect the tachometer, but, just enough<br />to be very annoying. You can actually hear the<br />speed change slightly in a steady rythm of maybe<br />+- 50 rpm's. This condition disappears completely<br />at around 4000 rpm's and the motor runs like a<br />top all the way to wot which is 5200 rpm's. I had<br />a knowledgeable professional Yamaha mechanic check<br />it out. He claims that the problem is definately<br />ignition and not fuel. He was quite confidant that<br />the power-pack was at fault. He loaned me another<br />used, but good, one to try. No improvement. He<br />checked the coils with a meter. Again, OK. He says<br />I should just use it the way it is. I can't accept<br />that. Can anyone offer advice ? By the way, I've<br />had the carbs off for cleaning. AOK. He also <br />found a plug wire with a lot of resistance. He<br />replaced the spring connector in it. Still no<br />improvement. WHAT GIVES ?<br /><br />THANKS.......<br /><br />P.S. - Initially believing the problem to be fuel<br />related, I replaced both fuel pumps, and all fuel<br />line. I also installed a Racor seperator. I even<br />tried running the engine from a 5 gal. jerry can<br />with a short length of hose. No improvement.<br />Also, I noticed on a fishing trip recently that<br />the motor ran great and exhibited none of the <br />symptoms described above ! The weather that day<br />was rainy with very high humidity. Could that have<br />an effect on the motor, or perhaps was this just<br />pure coincidence ?<br /><br />Thanks..<br /><br />Larry