1991 454 surging, no power under load...

[mkino]

I have a 1991 Sea Ray, 454 carbureted. Rebuilt the whole thing including the carburetor last year. Ran great for a while, then in February it wouldn't start. I replaced the fuel pump and filter, it ran fine on the hose. Took it out today, not so good.

I did replace the fuel pump with a Sierra rather than Quicksilver, and when I started the boat is sounded a little different, but seemed to run smoothly as I warmed it up, then it kept dying at idle. So I adjusted the idle, seemed fine. Left the harbor wakeless speed, seemed fine. When I took it up on plane, it was fine the first time, but then it started backfiring thru the carb a little and surging badly. At first it was OK up to 2200 rpm, if I gave it more gas it would surge and lose power fast. The top rpm level I could push it to kept declining, finally it wouldn't go over 1200 rpm without surging. Took it back to the dock wakeless and it continued to be fine under minimal or no load. In neutral, it was able to rev smoothly up over 4000 rpm, just under load, surging.

I'm thinking some sort of fuel blockage, but I would really appreciate your ideas, thanks in advance!

 

[Bt Doctur]

Re: 1991 454 surging, no power under load...

anti-syphon valve restricting the flow

 

[NHGuy]

Re: 1991 454 surging, no power under load...

Sure sounds like lack of fuel.
Did you change your filters? What broke the old pump? Maybe there are bits of stuff in the filters or the fuel inlet. Could be what killed the old pump. Or there could be parts of the old pump or gasket causing blockage too.
Best start is to check for blockages or fuel supply.
Sometimes folks will think they need a pump when there was actually a blockage or leak in the supply to the pump. So check the tank, lines, pickup, anti siphon valve, filters and carburetor inlet.

 

[Bondo]

Re: 1991 454 surging, no power under load...

Sure sounds like lack of fuel.
Did you change your filters? What broke the old pump? Maybe there are bits of stuff in the filters or the fuel inlet. Could be what killed the old pump. Or there could be parts of the old pump or gasket causing blockage too.
Best start is to check for blockages or fuel supply.
Sometimes folks will think they need a pump when there was actually a blockage or leak in the supply to the pump. So check the tank, lines, pickup, anti siphon valve, filters and carburetor inlet.

Ayuh,... Agreed,.... Verify that the fuel pump is pumpin,....

If it checks out, rebuild the carb again,... a year is long enough to corrode from crap in the fuel,...

 

[mkino]

Re: 1991 454 surging, no power under load...

Today I pulled the intake stem from the gas tank and siphoned out about five gallons. Looked good, no flakes of any kind... cleaned the anti siphon valve, everything looked perfect. So I thought spraying some carb cleaner in it while running might help. I sprayed for about ten minutes, then tried to adjust the idle back down to about 600, no good, stalling. Kind of works around 800, which is higher that it used to need to be. Then I tried revving it quickly, and it backfired thru the carb. So I'm convinced it isn't getting enough fuel. I'm thinking about going back to a Quicksilver fuel pump, maybe the Sierra doesn't pump enough...

Questions:

1) Is it possible that the Sierra is inferior to the Quicksilver fuel pump? How many PSI should it be pumping? I'm probably going to buy a fuel pressure gauge.

2) Is it possible that the metal fuel line from the pump to the carb is blocked? Kind of hard to take it out and clean it, but all the other fuel lines are new as is the fuel filter.

3) I took apart the fuel pump I replaced in January. It seems to have some strange whitish sandy stuff in it, which turns to dust when you rub it between your fingers. Any ideas as to what caused this?

Thanks so much for your help...