Low RPMs at full throttle

[c.adams]

I have a 1989 Bayliner Trophy 2159 with a 3.0 omc cobra, only had it a couple of months, will only turn approx. 3000 rpms at full throttle. I have checked the fuel pump, cleaned the spark arrestor, emptied the fuel tank, and put 93 octane non ethanol back in it. I pulled down the rubber hose between the riser and the L pipe and the shutter valve is missing, the shaft is still there. Today I pulled the outdrive off and so far have not found any evidence of the missing shutter valve, I was wondering where it is typically found when it goes missing. Is it likely to get all the way to the lower unit?

 

[Howard Sterndrive]

Re: Low RPMs at full throttle

shutter could be here:

a couple other things to check - advance weights and springs possibly all gummed up and rusty in distributor, anti-siphon valve could be stuck

 

[c.adams]

Re: Low RPMs at full throttle

I checked the anti siphon valve when I drained the fuel tank, and replaced the fuel line and both filters. I pulled the distributor cap off just to look, every thing looks ok, not gummed up, have not checked timing or dwell yet, pulled spark plugs they look good, there was one occasion when I throttled up that it got up to 3600 rpms, planed out and did good, but my omc manual calls for 4400-4800 at WOT.

 

[Maclin]

Re: Low RPMs at full throttle

What is the speed at 3000rpm?

 

[c.adams]

Re: Low RPMs at full throttle

Less than 20, won't plane out at 3000 rpms. The one time it turned 3600 rpms the speedometer showed 26 mph.

 

[Gilded_Splinters]

Re: Low RPMs at full throttle

Since this boat is somewhat new to you, you might consider that you have the wrong prop on it.

Is this a new condition since you bought it or the way it's been all along?

All of the suggestions you've gotten here are certainly valid, but wide open throttle and low RPMs is a direct equation to incorrect pitch.

 

[c.adams]

Re: Low RPMs at full throttle

My research says the prop is correct 13 ? X 15 3 blade alum.

 

[c.adams]

Re: Low RPMs at full throttle

I seperated lower unit from upper gearcase today, still have not found any pieces of the shutter valve. The only place left to look is the L pipe between the riser and the transom. I have looked through the exhaust bellows and have seen nothing, possibly going to try to rod out the L pipe with a piece of plastic tubing.

 

[Howard Sterndrive]

Re: Low RPMs at full throttle

I pulled the distributor cap off just to look, every thing looks ok, not gummed up,

you can't see the advance weights by just pulling the cap off. You have to remove the plate the points are mounted on.

 

[scott11]

Re: Low RPMs at full throttle

My 2.5 is basically doing the same thing as yours man other then i get a loud tick when the motor warms up over 140 degrees. You dont happen to have this problem on yours do you?

 

[c.adams]

Re: Low RPMs at full throttle

I don't have a tick with mine, it runs and sounds good from idle to 3000 rpms, just won't get past that 3000 rpm mark.

 

[scott11]

Re: Low RPMs at full throttle

Ok lucky you haha. I am going to try checking my dwell and points gap when I get back to Ontario. If that doesnt help anything im going to pull the carb apart. As for my ticking I will probably have to check out the valvetrain. I will let you know if I solve anything to do with the low WOT rpm.

 

[4Wins]

Re: Low RPMs at full throttle

Have you found the cause of the problem on this?

 

[c.adams]

Re: Low RPMs at full throttle

Have not worked on it in over a week, will probably do a full tune-up next.