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

OMC 5.7 1989 lacks RPM at WOT
 

"Jens_Erik" wrote in message
ups.com...
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


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

OMC 5.7 1989 lacks RPM at WOT
 

On 15 May 2006 05:52:18 -0700, "Jens_Erik"
wrote:
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?
================================

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.

OMC 5.7 1989 lacks RPM at WOT
 

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.

OMC 5.7 1989 lacks RPM at WOT
 

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.

OMC 5.7 1989 lacks RPM at WOT
 

I removed the flame arrester yesterday and the secondaries where
exposed. From what i could see everything on the top part of the carb
seemed to be able to move freely. But i did not open the carb entirely
and checked the carb core. I have not yet replaced the gasket yet as
they are not in stock here in Nuuk.

OMC 5.7 1989 lacks RPM at WOT
 

It's very possible you have vacuum secondaries. Which means the engine
vacuum opens them. If the carb is faily square and the secondaries are
significantly larger than the primaries then you probably have a quadrajet.
If the secondaries are the same size as the primaries and the float bowls
are square blocks on the front and rear of the carb it's probably a holley.
Inability for the secondaries to open would explain your problem. You have
to get someone to watch them while you are underway. They will not open
without a load if they are vacuum actuated.

"Jens_Erik" wrote in message
ups.com...
I removed the flame arrester yesterday and the secondaries where
exposed. From what i could see everything on the top part of the carb
seemed to be able to move freely. But i did not open the carb entirely
and checked the carb core. I have not yet replaced the gasket yet as
they are not in stock here in Nuuk.

OMC 5.7 1989 lacks RPM at WOT
 

OK. Then i will have someone watch the secondaries. The carb is fairly
square and the secondaries are larger than the primaries so it seems it
is a quadrajet.
So to have someone watch the secondaries I will have to run the engine
without the flame arrester mounted.
I will just mention that the rpm gets over 4000 with ease when in
neutral. Therefor it seems the engine is not producing enough power to
get over 4000 rpm or more when in gear.

OMC 5.7 1989 lacks RPM at WOT
 

OK. Then i will have someone watch the secondaries. The carb is fairly
square and the secondaries are larger than the primaries so it seems it
is a quadrajet.
So to have someone watch the secondaries I will have to run the engine
without the flame arrester mounted.
I will just mention that the rpm gets over 4000 with ease when in
neutral. Therefor it seems the engine is not producing enough power to
get over 4000 rpm or more when in gear.