rpm's

Hello; I have a 19ft. crestliner,3.0 omc cobra stern drive.I've try to inprove
my rpm's with no luck.I'm getting 38 to 40 rpm's,with a 3.0 I should be
getting better then that.


George

Re: rpm's

1st on the list is to make sure the engine is making full power. That means a compression check to insure the engine is capable of making full power. then a complete tune up. then inspect the outdrive for gear lube quality (no water/metal). Then check the bottom of the boat for growth if it lives in a slip. If all is good then start looking at the prop. Could be the wrong pitch and possibly, the wrong gear ratio if someone had issues and swapped the outdrive/engine.

Re: rpm's

the moter and the heads have ben rebuilt,an carbator ben rebuilt, had a tune,new prop with pich ok.this is why I can't understand the lack of power.
The man that use to work on it ,I'm never taking it there to have work done
on it,I get it back an have something else go's wrong.I new he was doing it on purpus,I've worked on car's and trucks to long,when it comes to boats well.I thought it might ben in the linkage,but was wrong.

George

Re: rpm's

I'm getting 38 to 40 rpm's

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My guess is that you mean 3800 to 4000.

new prop with pich ok

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What pitch is it? What pitch was the old prop?

the moter and the heads have ben rebuilt,an carbator ben rebuilt, had a tune

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Why was all of this done? Has the motor EVER run over 4000 RPM? Did it used to run higher before the rebuild and the new prop?

Re: rpm's

The moter was already rebuilt,when I got it. I had redo the heads because
water was getting in the oil,probly the heads wasn't tighten to spec.I don't
know for shure. I've got a 13 3/4 x15 pich the old one I don't remember what it was.I don't know how fast it use to run. Carb rebuilt to.

Re: rpm's

With only a 15 pitch prop, It's time to check the gear ratio of the outdrive.

Have you adjusted the trim of the drive while running? Full down and you will be plowing through the water and will never get full throttle.

Here is a list of things that can cause low WOT rpms.
In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully