1990 20 hp Mariner runs great but no top end

[rudewrencher]

I picked up a 1990 20 hp Mariner recently and went through it systematically .Good compression ,spark ,clean carb ,lu end lube has no water ,shifts well .It now starts and idles well but seems to top out at about 3/4 throttle .I checked all the linkage and it seems to be advancing properly but this is a make I don't have much experience on so maybe i'm missing something basic ,any ideas?

 

[fastjeff]

That model had (I think) electronic spark advance. You can tell ifthe trigger coil is fixed, or if it moves with the throttle.

If it's fixed, then the high speed circuit is not operating--either the trigger coil is burnt (which you can check with a volt meter), or the switch box is shot. But if the trigger coils move with the throttle...not sure what that could be (possibly over-propped?)

Jeff