5.0L runs weak only up to 3500 rpm

[GREGB1954]

Power is weak coming out of the hole. Once it planes and rpm's get to 3500 there is a strong power surge to WOT and it appears to be running at full power. It starts and idles perfectly. It revs just fine also when not under load. So the problem is weak power in the mid range under load.

I have been using mostly gas from gas stations (likely with ethanol). I put 2 cans of Seafoam in it with about 25 gallons of gas and ran it to almost empty. Then filled it with marine gas (no ethanol). It runs a bit stronger but has same problem.

Any suggestions?

 

[Bondo]

Re: 5.0L runs weak only up to 3500 rpm

Ayuh,.... Welcome Aboard,... Sounds like a Carb problem,....

What carb ya got,..??

 

[GREGB1954]

Re: 5.0L runs weak only up to 3500 rpm

It is the 2 barrel Mercarb. Boat is a 1999 Maxum 2100SR with the Alpha 1.

Seems odd to not have the problem all the way up to WOT. I used to work quite a bit on cars including carb rebuilds so that is my temptation with this situation.

 

[Volphin]

Re: 5.0L runs weak only up to 3500 rpm

Rebuild the carb and check fuel filter. If it doesn't have a water separation filter, add one.

 

[GREGB1954]

Re: 5.0L runs weak only up to 3500 rpm

I failed to mention that I did replace the fuel separator and drained the old one. It had some small amounts of debris and small amount of water. The incoming filter to the float bowl I also checked to and it was perfectly clean. So the fuel filter is doing its job.

I am close to pulling the carb. Just seems odd to have the problem only at mid range/rpm power band, and is OK after 3500 and idle.

Any thoughts on what circuit in the carb would cause this?

 

[Bondo]

Re: 5.0L runs weak only up to 3500 rpm

I failed to mention that I did replace the fuel separator and drained the old one. It had some small amounts of debris and small amount of water. The incoming filter to the float bowl I also checked to and it was perfectly clean. So the fuel filter is doing its job.

I am close to pulling the carb. Just seems odd to have the problem only at mid range/rpm power band, and is OK after 3500 and idle.

Any thoughts on what circuit in the carb would cause this?

Ayuh,.... Does it really matter, ya gotta rebuild the Whole carb anyways,...

It could be the hi-end of the low speed circuit, or the beginnin' of the hi-speed circuit, or it ain't transitionin' properly,...

 

[GREGB1954]

Re: 5.0L runs weak only up to 3500 rpm

Any suggestions on where to get a high quality kit?