[QUOTE=onesickpantera;3458503]I hate to say it but the fact that you're only turning a 21P prop to 5100 tells me you're down on power.

Personally I would try a 23P Rev4 and see what happens. But I'm guessing similar speeds at lower rpms.

Are you getting full timing advance? Jetted correctly for your altitude?[QUOTE]

I am not sure how to check if i am getting full timing advance. It was jetted in Hurricane utah now that i think about it. I boat at 4800ft it was tuned for 3200ft. Is that a big enough differnce to cause that much power loss? And also does anyone kno what the timing should be set at?

Timing 34* total. It may be a jetting issue...but as stated before, if your turning a 21p at 5100....anything bigger is gonna pull the rpms down into the 4500-4700 range. I think your down on power sir. My old boat (25' Chris Craft Limited) had a slightly warmed up 502 in it. I had a labbed 25p Mirage Plus on it...and it went 67 mph (GPS) at 5000 rpm's. Do you know what jets are in it now ? Did you look down the top of the carb to see if the throttle blades were perfectly vertical with the throttle pushed all the way forward (engine off) ? This will tell you if your throttle is adjusted right, and your actually getting WOT. Just an idea. :drink:

First problem I see is take that air filter and put it back on your lawnmower ! Get the biggest spark arrestor that you can find and try that , it will only help. You will need all the air you can get at that elevation . As stated with out running it on a dyno it's all just a guess ! It takes some good parts to make 600 HP, not just pretty one's . Just my .02

Fixx
 

I'm guessing the boat has foam cores and is saturated with water.. Find out what the stock weight is and trailer is and go have the boat weighed..