350 Mercruiser WOT RPM??

Hey guys!

Brand New to this sight, thought maybe you guys could help, Pleeeeaaaase!!

I have a 1990 Glastron CSS 19 with a 350 Magnum Mercruiser. Bought it two months age. Was told it was a new motor put in due to improper winterizing. Motor was apparently out of a GM van and rebuilt by a race engine shop. Apparently bored 30 over, new pistons,etc. Don't know what cam is in it.

Motor runs great, good compression. Here are the props i have tried. 23 pitch high five stainless, 19 pitch revolution 4(had to put a flat trim tab to use this one), and a 21 pitch 14 1/4 aluminum 3 blade.

Problem is the most RPM at WOT I get is around 4000 with all the above props and 50 MPH on GPS.

Boat has a new tach I installed. I get the same reading off the coil with a DMT that the tach shows. Is it possible that the reading off the coil I get with a DMT is wrong?

I know the 4 barrel carb does not open completely. Haven't had time to take the cable off and manually open the carb with someone else driving. If I adjust the barrel on the cable to open it full at the carb, it pulls it off idle and idles at about 1500 RPMs. Would it make a difference if the flaps on the carb are vertical about 75 -80 degrees, not the full 90 degrees?

Is it possible the cam needs to be changed?

How much does this boat weigh? around 2000 lbs.?

Mercury prop chart says it should have a 23 pitch 3 blade prop?

Any other ideas?

Help would be awesome,

Thanks.
Kevin

Re: 350 Mercruiser WOT RPM??

The tach set to 8 cyl. on the back.

The thing is less pitch more rpm if using the same sort of prop :ie 3 blade stainless.

Also lower top end.

That a marine carb?

What make alot of people know carbs here real, real well.

These race car guys put a high recovery oil pump in that bad boy?

Better not have gonna suck that pan dry and blow up ya motor.

This ain't a race car.

Re: 350 Mercruiser WOT RPM??

"Would it make a difference if the flaps on the carb are vertical about 75 -80 degrees, not the full 90 degrees?"

Absolutely yes.