1975 johnson stinger rebuild won't accelerate under load

I have a 1975 Johnson Stinger (orange and black) on a Glastron v-162 that was profeesionally rebuilt by a reputable omc dealer recently. New power pack, coils and rings, and a new lower piston. After running 2 6gal tanks at 25:1 oil ratio with great performance, switched to 50:1. Ran just fine. Next trip to the river it started fine and idled out past 6knot zone and boat wouldn't get up out of the water. Played with throttle hoping it would clear itself.Linkage ok. Switched tanks, no better. Seemed to shudder at WOT but had to just idle back to ramp. At home pulled plugs, they seemed fine, all 3 the same, just a little wet with gas. With muffs started right up and accelerated just fine. Got plenty of spark from all 3 cyl using a spark checker.7/16" hot blue cracking.Any ideas where to go now?

Re: 1975 johnson stinger rebuild won't accelerate under load

I realize you just had it rebuilt, however, mine had very similiar issues and my compression was low. Especially in one cylinder. I ran some seafoam through it, 2 cans. It runs in the water now.

Good Luck

Re: 1975 johnson stinger rebuild won't accelerate under load

check compression .

Re: 1975 johnson stinger rebuild won't accelerate under load

what do the plugs look like.

Re: 1975 johnson stinger rebuild won't accelerate under load

dsinger said:

what do the plugs look like.

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The plugs all three the same, .030 gap and just a little dark around the electrode insulation. The motor has only had 12 gals of 25:1 mix and maybe 2 gals of 50:1 since rebuild run thru it. The correct champion plugs. New fuel, no fuel line abnormalities, new vented tank, new fuel feed hoses.Spark advance moves properly..I dunno....thanks