242 ss rpm help
 

I have a 242 ss with brand new 454 mag and I'm only hitting 4000 rpm on the water I've changed the fuel filter I've only hit 42 mph ,I'm very frustrated any ideas or has this happened to anybody else ??? Also carb is not new But 1000 rpm loss really .......

What do you have on it for a prop?

and what drive?

Prop is 21 pitch mirage and bravo 1

My 7.4L (not the Mag) started losing RPM and speed. It turned out to be that the heads were rusting through and water was getting in the cylinders. Probably not the situation in your case, but when you say 'new' 454 Mag, it is probably a remanufactured, right?

I would check the basics, if you have not already . . . throttle linkage. You could clean out the carb high speed jets with starter fluid (a great solvent).

If all else fails, I would do a compression test and cylinder leak test to see if there are any issues with the engine, etc.

Make sure there is not excessive weight in the boat . . . water logged foam, etc.

Your engine should get up into the 4800 RPM range, 55 mph +/-

What do you mean water logged foam , the foam around the gas tank ? If so how would I check ??

there is foam around the gas tank as well as foam inside the stringer boxes either side of the tank, as well as in the aft stringer boxes that the batteries sit atop.

if there is a water source, then over time the foam will tend to break down and retain the water, making your boat heavier, etc.

Sometimes folks take their boats/trailers to a set of truck scales to see if the total wieght is within expectations.

I have the same issue.... 3900 - 4000 rpms is max.... New gas tank installed a couple years ago and it was dry as a bone so I am ruling out the water logged foam theory (for my boat at least) but I am dying to find a resolution to this as well.

had compression test, leak down test with good numbers
rebuilt carb
new electric fuel pump, filters, etc.

My kiekhaefer throttle only goes a little past 3/4 way before I cannot push it forward anymore... figured this was normal?

Well at least I'm not the only one