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50 cobra tops out at 3000 RPM

J

Jonny Peters

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"I have a 1991 5.0 Cobra with

"I have a 1991 5.0 Cobra with an OMC outdrive. When the boat is out of the water, the engine revs great. But when the boat is under a load it will not exceed 3000 RPM. I have replaced the fuel pump, filters and had the carburetor rebuilt within the past year. Nothing else (aside from normal maintenance)has changed. What could be causing the lack of power? Please help!!!!"
 
"Ayuh,.....

What you did a

"Ayuh,.....

What you did a Year ago is a moot point,.....

You'll have to Check,+ See if it's getting it's Fuel....
'Cause it sounds like it's Not....

Other-wise,... Do a Full,+ Complete Tune-Up, including Compression,+ Leak-Down tests....
That should tell you Where the issue is....."
 
"The fuel filter/pump were rep

"The fuel filter/pump were replaced in January and deliver 8psi to the carburetor, I will be doing a tune up this w/e so hopefully that will tell. Thanks!"
 
The prop (which is a 17&#3

The prop (which is a 17" pitch 14.5 " diameter s/s) has been looked at by the prop shop and is what the book calls for... someone suggested that it might be the anti-siphon valve. Could that be causing my issue? The general consensus is that it is a fuel or compression issue.
 
"[b]"deliver 8psi to the c

""deliver 8psi to the carburetor,"

Ayuh,....

Is that at WOT,..??

Has the motor ever been overheated,..??
Any Cooling Issues,..?? At All,..??"
 
"The motor has never overheate

"The motor has never overheated, and the fuel pump delivers 8psi at idle speed. I do not have any cooling issues... the engine never exceeds 180 degrees farenheit"
 
"Ayuh,..... I just borrowed th

"Ayuh,..... I just borrowed this from a Bud at another site,.....

Engine Won't Reach Operating RPM. Check

Fuel condition. Type and Octane possibly old fuel
Propeller pitch or diameter, damaged blades
Restricted fuel pickup tube or anti siphon valve Fuel System Test
Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
Marine growth on hull and outdrive
Wrong gear ratio in outdrive
Restricted carburetor air intake (clogged flame arrestor)
Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
Poor cylinder compression Compression Test
Carburetor defective, or wrong type.
Fuel pump pressure and vacuum
Boat overloaded, improperly loaded, or improperly trimmed.
Engine Overheating
Engine timing and ignition system operation
Remote control cables and linkage for proper travel to open throttle plates fully."
 
Thanks! I have a good list of

Thanks! I have a good list of things to check... I just want to know what's wrong with the stupid thing so that I can go back out on the water!
 
"Are you sure you're getti

"Are you sure you're getting full throttle travel. check your cable rigging, make sure your cable housing is not slipping at the control counsel, and just the cable it-self is moving. Out of the water under no load it may seem like it's full open..... but it may not be."
 
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