RPMs at a total loss

[Davenc]

1986 Bayliner 28'. New 260a. Every thing that can be new is new. Switched from old style distributor to Mallory electronic. New wires, plugs and Carb. (Third carb actually.) New manifolds and risers. Timed perfect, no vacume leaks. No fuel restriction problems. idles perfect. Runs well at low speeds. No oil problems, compression checks out great.

Problem is no RPMs under load. The prop is exactly what the manufacture suggests.15"L 19 pitch No dings no chunks missing no nuttin. RPM gauge has been checked and is accurate. The bottom is cleaned monthly.
The boat is turning 3000rps at wot. I have had this problem almost nine months now and have had a marine mechanic do several different things to try and fix the problem, zero luck.

When in gear and moving at a decent speed there is a slight vibration. There is no slipping, no noise.

Could this be an out drive problem? I would think there would be some indication of a bad outdrive. I am more than willing to pull the boat out of the water but hate to if there is no chance of the out drive being the problem.

This is driving me crazy, please help.:%

This is a Volvo Penta OD.

 

[rodbolt]

Re: RPMs at a total loss

thats a lotta wheel for a 28 ftr.
there are a few places that have the volvo adapter for the IDC dyno.
I sold mine to rons marine in portsmouth VA. if thats all it will turn be aware its seriously lugging the motor.
I would drop to a 15x15 and work back up to the 19. also check the ign timing pointer for any mis reference. in other words bring the engine to TDC by using a piston stop or similar device and isure the marks agree with the pistons physical location. then insure the timing is advncing correctly at WOT.
when ya say "new"250a, is that new to you,new remanufactured or brand new crate motor from volvo penta? I have seen a few reman motors with the wrong camshaft do exactly what you describe.

 

[calwldlif]

Re: RPMs at a total loss

I'll be the first to ask
have you weighed the boat?

 

[paulie0735]

Re: RPMs at a total loss

what gears? anything could have been done to that drive over the years. I'd like to see you get the timing verified against actual piston position not just where the marks say it is. Also agree with rodbolt re the engine, when you say 'new' is what exactly?? Bottom line is simple enough, if all is fine with the engine and boat and it still won’t pull the rpm than you're running to much prop for the engine / boat / drive package.

 

[Davenc]

Re: RPMs at a total loss

The engine is a reman. Maybe five or six hours on it. We have checked the timing mark several times by bringing the #1 to tdc. Its fine.

I guess I will pull her and re prop her. Seems to be the only thing left.

Thnx

 

[rodbolt]

Re: RPMs at a total loss

when I say verify the marks, use a piston stop tool or dial indicator on number 1 piston to find TDC, then look at the balancer and tab to see if they agree with the physicall location of the piston.
also try to get the cam specs, if its a reman cam its possible its not indexed correctly.
where did the reman come from?
some places are not so good.the 260 motor used a rather aggressive marine cam and a decent set of heads. if yours does not have them it plain wont make 260 horse power.

 

[Don S]

Re: RPMs at a total loss

You mentioned you have had the problem for 9 months. Does that mean it worked ok before that or that is how long you have owned the boat?
If it has been this way since you owned it, I would verify the gear ratio in the drive. If someone replaced it with the wrong one, you never will be able to make it right.
It's easy to check put the drive in gear. Remove the coil wire so it won't start, then slowly bump the starter over (use remote start button) and count the number of revolutions of the engine to get exactly 1 revolution on the prop.

 

[Don S]

Re: RPMs at a total loss

You mentioned there were no restrictions in the fuel system, but how about an air leak. Might want to test it per this thread.

http://www.iboats.com/bbboard/bbBoard.cgi?a=viewthread;fid=24;gtid=1107009

Here is a list of the possiblilities of things that will cause low WOT rpm.

 

[Davenc]

Re: RPMs at a total loss

You mentioned you have had the problem for 9 months. Does that mean it worked ok before that or that is how long you have owned the boat?
If it has been this way since you owned it, I would verify the gear ratio in the drive. If someone replaced it with the wrong one, you never will be able to make it right.
It's easy to check put the drive in gear. Remove the coil wire so it won't start, then slowly bump the starter over (use remote start button) and count the number of revolutions of the engine to get exactly 1 revolution on the prop.

Don, when I purchased the boat the engine was shot. I knew that going in. What is scary is the bad engine performed about the same as the new engine. Thats why Im thinking outdrive. I will go and do what you suggest, and post the results.
Thnx