Re: ’83 15hp, no power at top end

[johnyrude200]

I switched carbs prior to posting, 1 was #56, the other #58, no significant change on the jets in terms of influence on performance. This one has me stumped. Changed leaf valves and while the motor gets about 400RPM more now, it’s still topping out around 4200-4300RPM. Idles down low to 600 RPM smooth no problem.

Switched powerpacks, switched the float inlet orifice to a larger one, no difference. It’s as if it’s not getting enough fuel at the top end. I went as far as to switch fuel pumps, and the lines are all clear and new.

It’s not bogging down at the top end, smoking excessively, or blubbering, it still runs smooth, just won’t max out in RPMs as it should. It does not stall out at any range. I’ll try a 3rd high speed jet.

One thing of note, it appears this motor >might< have been overheated at some point because the top of the block and cylinder head are a light/medium brown (it’s a white block). So while compression numbers are still 110-120 (OK), I’m wondering if somehow the cylinder head has been affected/distorted. It was necessary for me to change out the head gasket as it was leaking initially in multiple areas.

It seems that these 9.9/15’s run hot on the top of the cylinder even when the cooling system is OK, and it takes awhile for the thermostat to get warm enough to open. So while the top of the cylinder may be 170°, the bottom where the thermostat is may still only be 100-110°, and the actual cylinders themselves (from the port side) are only at 100°.

I did not see any major scoring on the cylinder walls when I removed the head (top cylinder had minor scoring, nothing too major).