how to tell if an engine isn't making full power?

[lime4x4]

i have a 86 searay 268 weekender. I rebuilt the engine about 2 months ago.I installed an electric fuel pump as well. Also did a full tuneup.This is a 4bbl carbed engine. the engine starts and sounds great. When in neutral she will tack right up with no problem.But when i try to accell she shoots right up to 3 grand and then takes a long time to hit 4000. I've tried numerous props and i still can't get the engine to hit 4600. This boat had the wrong ratio drive 1.98. When we first took the boat out with the wrong drive it would tach up to 5000 easily with a 17 prop but wouldn't really move the boat.then i installed the correct drive 1.47 with the same 17 prop my max is 3500 then installed a 15 and i'm up to 4000 then a 13 i hit 4500 but accell is way down.The 15 gives me a max speed of 36 mph the 13 gives me 18 mph. I just want to rule out engine problems.the engine is a 350 mercruise with thunderbolt ignition.timing is at 8 deg btdc and the timing mark advances when checking with timing light and opening the throttle

 

[mkpj1]

Re: how to tell if an engine isn't making full power?

Compression test the engine. Dry then wet if you find a variance between cylinders. I like a vacuum test as well. A strong engine is going to pull good vacuum.

Remember a new engine is going to be "tight" for awhile. In a car it takes a 1000 miles or more before I feel it loosen up and she just flies, ya baby!

Good luck!

 

[Sorrento 25]

Re: how to tell if an engine isn't making full power?

I have a similar problem with a 7.4 on almost the same boat with an unknown gear ratio, but the same performance also on a 15. Someone posted recently that Don S. had posted a chart with 5 possible causes of low WOT RPM somewhere but I couldn't find it.

 

[cooter2506]

Re: how to tell if an engine isn't making full power?

Engine Won't Reach Operating RPM. Check

Fuel condition. Type and Octane possibly old fuel
Propeller pitch or diameter, damaged blades
Restricted fuel pickup tube or anti siphon valve Fuel System Test
Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
Marine growth on hull and outdrive
Wrong gear ratio in outdrive
Restricted carburetor air intake (clogged flame arrestor)
Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
Poor cylinder compression Compression Test
Carburetor defective, or wrong type.
Fuel pump pressure and vacuum
Boat overloaded, improperly loaded, or improperly trimmed.
Engine Overheating
Engine timing and ignition system operation (Full tuneup done recently)
Remote control cables and linkage for proper travel to open throttle plates fully.
This is copy and pasted from Dons post from another thread