Need some Help on Sluggish boat Please!!
 

Got a 19Ft Four winns U-19 with a Volvo Penta 5.7l GL, Brand New Holley 4bbl 600cfm. Engine Fresh rebuild late last summer. Not sure if I got a carb issue or running the wrong prop size. Only running about 53-56mph and only getting 4100-4300rpms. I know the boat is more than capable of running 60+. Start to push pass 3/4 throttle and just wants to die out(not stall). Hesitates and sometimes powers up for a fraction of a second and then back to hesitating. It should be getting enough fuel. I was told by my mechanic that my pump puts out more than enough gas gph for the carb. Before I spend a bunch of money to get it dialed in, I am hoping someone has some suggestions I havent thought of yet. Prop is 3blade stainless 14.25x23 on a VP sx outdrive. Not Duo-prop. Thanks

Change both fuel filters to be sure there is no blockage.

Check your total advance on your ignition timing, should be in the mid thirties.

Have you had it running properly since you put the new carb on? Since the rebuild?

It could also be dumping too much fuel killing the spark. Too big of a power valve or having the power valve come on too early or late

I had a different carb and manifold before the rebuild. New airgap manifild, marine carb and ignition. I am assuming that it was done correctly. All done through Volvo penta mechanics. filters are both new. got a 1 yr warranty. I should just bring it in before the warranty is up.

Double check water separator. Maybe full of water.

look for a check valve in the fuel line it will look like a regular brass fitting could be sticking

Hell yeah that changes everything. Change the water separator (should always be done in the spring, not the fall) and if that is not the problem take that baby back

You are describing an engine starving for fuel. I agree with the other posts. Tank check valve, fuel lines or filters.

You should not assume anything !!!! And yes if it is still under warranty get it back and let them fix it. Just my .02