Rpms limits at 3000

Have a 89 luhrs 40 454s around

Have a 89 luhrs 40 454s around 800 hours new boat just pick it up from maryland and trucked up north in the winter..Full throttle with tanks full of gas and 4 blade 24x24 props it only revs to 3000-3100RPMS 22knots per hour...I thought 454s should be cruising around 4000RPMs By the way in neutral with no load engines will rev 4000--5000 RPMs Any help will be appreciated..

"Here's the usual list:

"Here's the usual list:

1. Tune up: timing spot on (and advancing fully)

2. Carbs opening all the way and functioning correctly

3. Bottom clean

4. Props in good shape

5. Good compression on the motors (they could be a bit wheezy), and

6. It might just be heavily loaded. You have full tanks--how about all kinds of extra stuff on board?

Jeff"

"Thanx Jeff...props are in goo

"Thanx Jeff...props are in good shape..bottom is clean...compression is normal.. the weight is around 28000--29000 pounds i guess with tanks full and 5 people on board..i will have to check timing,,,but again both engines stop reaving at 3100 RPMs Also may have to double check gas lingage since the flybridge and console was removed for shipping..Is there a simple way to check that the 4 barrels open all the way on the carbs?"

I would think your overpropped

I would think your overpropped. The boat is making the speed but the rpm's aren't there. My 502 will turn a 23x24 3 blade to 4000. Stu

Thanx Stu You may be right the

Thanx Stu You may be right the boat came with 2 sets of props The set iam using now 24x24s 4 blade and a 3 blade 23x24s i believe wich i havent use them yet Is it safe to run the engines at 3000 RPMs for the rest of the season without doing any damage? And next season i can switch to the 3 blade set up and see the difference if any

"Hi Peter, I would either haul

"Hi Peter, I would either haul the boat or better still find a diver who does prop changes. If you're sure about the size of the wheels on the boat now a propellor rebuilder would be able to tell you exactly the size prop you would need to get to 4200 wide open. Have the three blade wheels repitched if necessary and have a diver swap them out. You won't have to haul the boat. Running overpropped will put a big strain on the engines. Stu"

"Stu- Please explain the term

"Stu- Please explain the term "overpropped" I've got a similar problem on my 34' Luhrs with twin 454's. Low RPM's (2900-3000) max at WOT - 12-13 mph max. I'm running 3 blade, 17" props -
Thanks-
Mike Austin"

"Hi Mike, every boat and engin

"Hi Mike, every boat and engine has a spec for max rpm. It all depends on the horsepower, hull type, weight and trans ratio. The engine manufacturer gives a spec for wot rpm's. If all is right the engine will run at that speed with the throttle wide open. Too little pitch or too small prop diameter will cause over revving. Too much pitch or too much diameter will prevent the engine from reaching max rpm. All this assumes proper running engines and a clean hull. There are several programs out there to help you figure out if you're at least close. http://www.castlemarine.co.uk/download/propinst.exe
Stu"