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Hey fellas, I'm at my wits end here, so Im gonna see if you guys have any ideas. I have a 2004 40 horse Yamaha 2-stroke on my duck hunting boat. Purchased brand new last October. About I month after purchase, motor began to drop Rpm's when crusing, as if it's dropping a cylinder or something. (3 cylinder motor) I have checked, checked, and rechecked for problems. No air leaks in gas tank or fuel line, checked plugs, checked fuel filter. Gas is of good quality and have used stablizer/conditioner as recommended. Thats all I know how to do myself. Have had it at the dealer 3 times, now, everytime, they have told me that they have checked compression, ignition, yadda yadda and nothing is wrong. In addtion, everytime they have come along for a test run, the motor runs fine, making me look like a fool. I am planning on taking it back in again, but with nothing new to tell them about the problem, I dont know if it will have any effect. This intermittent problem destroyed my hunting season last year, and I dont want it to happen again. I spoke with a Yamaha mechanic who mentioned that he has heard of Yamaha 40's and 50's having faulty power packs which will drop a cylinder? Any of yall heard of this?? Any help would be greatly appreciated, as Im about scream. Thanks
 

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Anytime you start dropping cylinders the main two suspects are the power pack and stator. Since the problem takes a while to act up I would target the power pack. Something in there probably isn't liking the heat. PP's can act strange as the temperature of the module changes. You'll need a manual and vohm at a minimum to test the PP. I've never worked on a Yam so I don't know what's involved in their tests.
 
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