issue with top speed

[scottschmitt]

My 89 SupraSunsport 351 PCM has lost some on the top end. We spent the last part of the summer focused more on wakeboarding than skiing, because our top speed seems to be ~32. The engine purrs just fine at idle and will rev to 4500+ at idle. At WOT I think we are getting ~3500 rpm.

The boat lives on the water. The bottom was painted with anti-scum paint ~5 years ago. It has some gup down there, but not bad. The transmission was leaking like a sieve, so we dropped it off at an inboard shop last winter. They pulled the tranny and we had Fantastic finish marine rebuild it. The transmission is back in and not leaking, so great. We were planning to get the boat re-painted, thinking that might be the issue with top speed.

For various reasons, the shop has been slow on repainting and we had a repeat conversation about the speed issue and that being our interest in repainting. They looked at the gup on the bottom of the boat and think it is not too bad and maybe we are loosing 1-2 mph from that issue.

I think I will pick up the boat without the paint and see how we run. I'd like to get back to skiing though.

We had OJ rebuild our prop last summer and that didn't help.

We had changed the cap, rotor, points, and wires ~3 years ago and they still look good. The dwell time is good. Plugs changed last year. Fuel filter changed.

The carb (Holly) was rebuilt ~4 years ago. I've adjusted the idle mixture screws a little bit at idle and the engine feels good at 1600 rpm. There is no vacuum leak that I detect spraying carb cleaner around the carb.

The fuel pump is original, and there is no fuel in the external hose. I am getting spark to each cylinder and the exhaust ports feel warm from each cylinder.

If drag isn't the major issue, is this likely a fuel problem?

So, things I can look at. Compression, but I don't think this is it. Fuel pressure at the carb. Fuel filter at the carb. Timing advance. Rebuild carb.

What is most likely?

Thanks.