Loss of RPM and TOP Speed
 

I have a 26 Searay OV with a rebuilt 454 330 Merc i have always (since i owned the boat) got 4600 RPM and 48 MPH ( i know not as fast as most of you guys :angry-smiley-055: ), well last year for some reason i lost 300-400 RPM?

I have tried everything i can think of:

New Prop 19 Mirage (old one was the same but had dings)
New Wires
New Plugs
New Cap & Rotor
New Fuel Pump (had and still getting 9psi pressure)
New Carb Rochester and Edlebrock both tried Edlebrock is on now since it idle smooth and runs great with it.
New Fuel Filter
Cleaned K&N air filter
Tried High Test with Octain booster
I have through Hull exhaust so no restrictions
Timing is set to 10 degrees / advances to 30
Did a compression test

I think i covered all i have done with no change in the results.
Here is another kicker say i get 4300 rpm with low fuel and one person and then i fill it with fuel and a couple more people my top speed 42 (curently) and RPM of 4300 will not change of corse it does if i really load up but under basic conditions it will not.
I can get the motor to run up more RPM by trimming more but at that point i am losing speed from cavitation.

If any one has any ideas for me they would be greatly appreciated since i need every bit of speed to try and keep up with you go fasts!

Thanks in Advance!
Jason

Any strange noises, or flat spots, or does it just quit winding a that rpm?

I would try your old prop again. You stated that it had a few dings in it- that might be enough to give you a few hundred rpm back, gaining some speed since the engine would be running at the best rpm for hp again. I would also put a little more timing in, try 32 deg and see if that helps.

Besides for the loss of RPM i purs like a kitten. It idles at 650-700 (lower if i want) smooth as silk. At WOT it does not hesitate or bog just will not rev up to the original 4600.

Thanks for asking/posting

Had problem both with old prop and the new prob.
thanks!

Verify tach and then check lower unit, look for sparkles.

Julie

Did this happened right after the rebuild?????

I agree, advance the timing to 32*

Do a compression and/or leak down test.

The rebuild was done a little over a year prior to this happening. advance timing to 32?? Did not know i could change that how do i do that? I know how to set initial but thought the advance was Hard Set? Sorry if i sound stupid. Also not mater where i ahve put the timing 6, 8, 10 etc the top end has not changed?

The total advance is set and can not be changed but if you bring up your initian to 12 and your total will be 32......

Not sure if that is a great idea or not. I can not remember what total is sapposed to be on those things....

Damn dude only 35 posts in over 5 years..... you suck!!! LOL

Flattened lobe on cam