tienken

Some advise please...

I just put a new (454) motor in my 1987 Checkmate Convincer 25' last year with a performance increase of approx 100 hp between cam, intake, card, fireball ignition and distributor... With that in mind, the motor is now only turning 4000 RPM's as it did with previous the old motor. The new motor seems to pull real hard with the new cam @2500 to 4000 and seem like it wants to go more but it stops due to not more throttle left... According to the cam (lunati) manufacture it should pull like a train up to 5800...After taking the boat out of the water after a long run I have black exhaust residue all the way down to the water line where the boat to on plan...

At this point, I'm not sure what the next STeP is to get the most out of my new motor.. Do I re-jet the card first? change timing? or do I change the pro?p... My other thoughts were portable dyno in the NY area

PatriYacht

Could you list all components in more detail?

ragtop409

Do you still have the small valve p-nut port heads because what you describe sounds like a 468 ci I had in my burb. Rag's

Pure Energy

1st thing is to check for WOT. Put the throttle all the way forward and look at the carb to see if it opens all the way. Your linkage may need adjusting.

If the transom is that black it may be running too rich.

Did you test run with the same prop? With 100 extra HP, you should be able to go up a couple of pitch.

I know nothing about fireball ignition. Someone else will have some more info for you.

blue thunder

Definately need more specifics on engine. Also what pitch prop and how many blades.

BT

tienken

The prop is 14.5 X 20, out drive is a OMC King Cobra... What additional information do you need on the motor??
The motor is a OMC 454 motor, edelbrock 750 carb, with a edelbrock performer intake and new electronic ignition.. The throttle assembly is all the way open at the carb @ 4000 rpm's.

blue thunder

What the heads are and the specs off the cam card. It is possible if you have small oval port heads that performance (hp) has not been improved. Was any head work done?

BT

Pure Energy

Just asking, how do you know the carb is open @ 4000 rpm? Was someone back there looking while underway?

formula31

Ut oh, cam and intake change wont do much without heads and exhaust too. The cam must match all the components including compression. If someone talked you into a big cam without doing all the other stuff the engine may run worse.

But I would check ignition advance at wot first.

blue thunder

If no tuning problems are unearthed your only good play is to pitch down to about a 17p prop. Very hard on an engine to run it outside of the recommended WOT rpm band. 4600rpm should be about right for your engine.

BT