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OMC 5.7 1989 lacks RPM at WOT
I just bought a used Bayliner Trophy 23 foot and the engine is OMC 5.7
1989 (model 574 APRMED), i believe it has 250 HP. The prop is 15'' x
17''. But the max rpm I get is 3400. Is that the maximum rpm on this
type OMC engine? I should think it lacks at least 1000 more rpm. I
believe the engine should be able to get at least 4400 rpm at WOT. The
max speed i currently get is just 24 knots. The engine seems fine and
I just replaced the spark plugs. Anyone has ideas of what could be
wrong?
Thanks
Jens-Erik
Nuuk, Greenland
My boat: http://www.123hjemmeside.dk/Nukappiaaluk/1442331 |
Jens_Erik
May 15
2006
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| Thanks for your replies.
I will check the distributor and the carb (it=B4s a 4 barrel carb).
Another thing about the carb: It is leaking just a little bit when I
pump gasoline in to it just before I start the engine. It is leaking
around the corner where the secondaries are placed, I think. I am
thinking of replacing the gasket. Any other thing i should be aware of
regarding leaking carb? Or will it be enough just to replace the gasket? |
Jens_Erik
May 16
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| I'd replace that gasket before I do anything else. But you might want
to open the carb up and clean it out in the process. If the float is
stuck, or the jets (the secondaries in particular) are clogged it will
cause problems. |
Capt
May 16
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| It's hard to tell, not knowing what the original prop was, how much that
boat weighs, (is it waterlogged?) or how you have it loaded. Assuming there are no problems with the engine, coil, carb, etc., it is
possible that the previous owner installed a higher pitch prop, thinking it
would go faster (common mistake). FWIW, one of my first boats, a 1982
Century with a 5.7 L engine and alpha drive had a similar prop (17 pitch)
when I first bought it used and the engine would only get to about the same
RPM (3200-3400). I had to drop to a 12 pitch prop to get the RPMs up to
over 4200. RCE |
RCE
May 15
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| It is difficult to say what the problem is but something is definitely
wrong. I have the same engine in a boat of about the same size and
weight and it tops out at around 4400 RPM and 31 knots, also using a
15 x 17 prop. Have a good mechanic check out the engine. It could be anything from
poor compression, ignition problems or the carburetor, but it is not
developing full power. |
Wayne.B
May 15
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| Jens-Erik You should be getting more RPM's out of the boat. Two things I would
look for. First, I would remove the distributer cap and make sure the
advance isn't stuck, holding the rotor you should be able to rotate it
freely about a quater turn in one direction, and it should snap back
when you let go. If that's stuck some silicone spray should help free
it up. The next thing I would look for is the secondaries on the carb,
if it's a four barrel carb. With the engine off place the throttle at
full throttle. The secondaries operate by either mechanical or vaccume
action. The mechanical linkage should move freely, if it's mechanical.
If it's a Holly carb it has vaccume secondaries, again, make sure
everything moves freely, if it does you may need to repair the vaccume
secondaries (it's easy, just get the part and replace it). Also, make
sure that little hose going to the vaccume actuator isn't leaking. |
Capt
May 15
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