Boat dies out above 3000 rpm

[trailshredder]

90 Regal 360 with twin 7.4L Mercruiser bluewater Inboards. Runs strong until I hit about 3,000 RPMs then my starboard engine looses power and stumbles badly. If I try to throttle up more when it does this the RPM will actually just keep dropping. If I back it down to 2800ish RPMs, purrs like a kitten. I have changed the fuel filter, Carb was rebuilt 2 seasons ago, was re-timed last year. Thoughts where to begin?

 

[greno]

Sounds like a fuel restriction somewhere. Put a fuel pressure gauge on and watch it while you throttle up.

 

[wellcraft-classic210]

It does sound like fuel delivery

If any Debris gets caught in the check valve located where rubber fuel line attaches to the tank that can cause the issue you describe. It the first restriction in the line size. A visual inspection & compressed air cleaning may help.

If the fuel filer has not been changed since the problem started -- I would consider replacing that also // pour the fuel out of the used filter into a clear container to look for debris

 

[Bondo]

Ayuh,...... Pull the fuel filter, 'n inspect it's Contents, for anything but clean fresh gasoline,.....

 

[trailshredder]

As I mentioned, the filter has been changed. I might add that I did pour the contents into a mason jar and there is no separation (water/gas) and it is very clean. I will give the check valve an inspection. Can compressed air be blown back into the fuel tank, through the check ball?

 

[achris]

They have Q-jets, yes? And that sounds like just as the secondaries start to open. I'd be looking at the carb internal secondary supply... Check the hangar hasn't dropped the rods, and things like that...

 

[trailshredder]

Yes, Q-Jets. Are these the linkage rods on the outside of the Carb?

 

[Maclin]

Internal, hang down from the secondary plate I believe. Part of the secondary fuel metering, to vary the fuel enrichment as they open up. There is a spring mechanism that keeps tension on the plate controlling the opening rate, the rods move with the plate.