I'm measuring fuel presser at the aeromotive reg now, i had it on the carb fuel line last week, my real problem is i cant get to 56-5800rpm, i have a MSD set up, i bought that becuse i thought the thunder bolt merc had a rev limiter holding me back, i have went up and down on props , carb jets sizes w/o any real change,( just returned from a high speed run trying 86p 6.5pv 97s ( see pic of black rich exhause sut ) i have went down to 72/87 with no real change, it runs fast up to the 72-75 mph range. i changed back to 86/92. my 253 checkmate i have done everything i can think but sink it, I have a marige 25p that goes a fast as my 24p maximus of my 25p px5 hydro, added a 1 1/2 spacer between the lower thinking the -2 was hurting did not change much i removed it a few weeks ago., 3/4 or 1/4 tank really does not change top end. I had a BG 850 last year, one thing is that if I overtrim i would think the rpms would go up but no change , I can turn a stock b1 24p at 5400 but speed is 72mph rpms go up and i burn more fuel, i checked all my fuel lines today even removing them from the tank.

The black soot on the transom is another indicator that you you are not running out of fuel or lean. It seems likely that your peak HP has been reached at around 5000 RPM. Was any dyno testing done on this engine?

no dyno testing was done. thanks

when i first got my 28 aerotek it had a beck racing 509 in it.the engine dynoed at 607hp at 5900.it would only turn 5000 with a 25p 3 blade so i put a 24p 4 blade and it would turn 5300 72mph.so i put a labbed 26 4 blade i t still ran 5300 but ran 74.2.i put a bigger carb,tried the spacer on the outdrive too.never could figure why it wouldnt turn anymore rpm.50 hp difference from 5300 to 5900.got tired of spending $$ so left it alone until it finally broke an ex valve.if your pressures and all are ok and its making power maybe thats all its gonna make.just my thought.

I was waiting for someone to mention exhaust valves. I had too small of a fuel pump on a 505" motor and it leaned out on the top end. Went like hell right before it spit the head of an exhaust valve out the header. Of course it was after it bounced around in the cylinder long enough to crack the cylinder and wipe out the top of the piston and combustion chamber. After that I put on a larger pump and a set of Manley Inconel exhaust valves. From what I've seen those valves are pretty much a must in a high performance marine application. Haven't had a problem since. Looks like you got plenty of fuel delivery now. Maybe that's all your going to get out of that motor.

I removed most of my extra stuff from the boat this week, wt does not really affect the top end, I will be out on a run this weekend and hope for a steady 75mph gps. thanks, glen