Fuel starvation on new rebuilds.

[Rusted Nut]

fresh Gen V rebuilds in a 370da installed and was breaking them in yesterday.
Up to 2800 both were strong and responsive. If seems when the secondaries are opening the stbd engine fells off( doesn’t die drops6-800 rpm) and is non responsive.
Both are strong coming on plane,never a stumble until getting into the secondary.
Stopped and switched fuel to be pulled of the port tank only- then the port engine stumbled and the stbd run flawlessly.
Ten minutes or so later it returned back to the stbd side.
Trip was throttling up and down, stop and goes burned 37 gals.
Both Weber’s professionally rebuild and tested last summer and ran well with the old motors.
New fuel and water seperaor filters installed. Thanks

 

[Strecker25]

Seems a lot of us are dealing with fuel starvation this year. Did you see the long thread from @370Dancer ? His are mpi, but same principles apply. Could be collapsing hoses, sediment in the system, or just a clog at the pickup ( although you said you switched)

I’d start with monitoring fuel pressure at those revs with a mechanical gauge. That will at least tell you that it’s actually falling off

 

[PlayDate]

I agree it sure sounds like a fuel pressure problem. Are the fuel pumps mechanical?

 

[Rusted Nut]

93 gen v mechanical pumps both new in 2015. Last summer the old tried engines pulled to 4K. Not saying two pumps can fail at the same time but- the starvation was switching from one to the other. Thinking one getting another set of filters for the water separator, read of the 10 micron filter can cause flow issues. Not sure what I put in I just know they fit.

 

[PlayDate]

It does sound like they are running out of fuel. When mechanical pumps stop creating pressure it shows up under load around 2000-3000 rpm and the motor runs out of gas. You have to get a fuel pressure gauge in line before the Weber and see what is going on. If you have a steel line from the pump to the Weber......make one up out of rubber with a fuel gauge on it with a couple of hose barbs. Max pressure is only 6 psi but it shouldn't fall off as the rpms increase.

I wouldn't replace anything until you know the existing fuel pressure under load between 1000 and 3000 rpm. Once you know that....the rest is easy.

 

[dtfeld]

I'd check/replace the fuel filters. May have some issues there and they are cheap and easy to inspect/replace. Could be something from the fuel tank, maybe a slug of water from being stored? Cut them open if need be to see whats there.

If that doesnt clean it up, go to the more invasive steps...adding the fuel pressure guage.