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I bought this old 340 for my son and he's just begun his 3rd season with it. I took a buddy's advice when looking for an old sled to find a nice clean Yamaha 340. It's been great and has provided hours of enjoyment. Up until now the only issue we ever had with it was the coil wire detaching from the coil body. I was able to carve back the plastic/rubber far enough to solder it back on, taped it up for safety, and never looked back.

This season it fired right up and was working great until just recently. It still starts up fine and after it's warmed up for a minute or so, we can do a few rips with it but then it loses power, sputters, coughs, pops, misses, and just won't rev up any more. You have to kinda feather it back to the garage.

- I've swapped plugs, no change
- I've swapped coils, no change
- I've cleaned the carb (it was fine), no change
- compression when warm 100/105 psi
- sprayed brake cleaner on PTO side of crank and intake gaskets, no change

I've attached a picture of the plugs and they are light brownish, but maybe just a touch lean? Also the oil pump setting is threaded outwards from the carb bracket to the max (for max oiling). And, we also put a blurp of oil into the gas tank for safety.

I have another '81 Enticer here and thought I could swap CDI's, but the wiring connections are not compatible.

Am I missing anything else????
 

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