Engine dies under load above 2500 RPM

[edhorv59]

I just installed my 4.3 carbuerated engine - new heads, plugs, wires, coil, water pump, manifolds, etc. Everything but lower end. Good compression, rebuild 2 bbl mercarb.checked fuel pump pressure (rund from 7-8 psi) removed anti-siphn valve, checked plugged vent. I have an new SEI replacement drive for my Alpha One, Gen 2 (SEI116). The engine runs good in the driveway and at the dock in the water at all speeds - UNTIL i'm on the water with the prop engaged running at about 3000 rpm at which point the engine drops off quickly until I throttle back below 3K. I have tried a new coil, checking fuel pressure, removing anti-siphon valve, opening the gas filler cap. Took off top of carb took for water or contaminants, removed and checked new fuel separator twice. Checked timing. HELP - not sure what the problem is! NExt stop is calling in a marine mechanc if y'all can't help. Appreciate any ideas. THanks

 

[Benny67]

Did you check the fuel filter on your tank?

 

[alldodge]

What year is the motor and does it have points or electronic ignition?

Take a 5 gallon gas can and stick the fuel line going to the filter down in it

Install a fuel pressure gauge between pump and carb and leave it there to watch what it does when running

 

[Rick Stephens]

I'd be considering redoing the carburetor rebuild. This sure sounds like it is misbehaving. Make darn sure the float is at the correct height. And check every passageway to be certain it is clean and open. And don't feel bad, most common repair needs redoing.

 

[GasCan II]

I just had what sounds like the same problem. Turned out to be the fine mesh screen on the end of the dip tube in the gas tank was clogging up with a small piece of what looked like a plastic bag .Removed the dip tube and the screen.Now the fuel/water separator will pickup anything but won’t shut motor down.

 

[Tycer]

I just had what sounds like the same problem. Turned out to be the fine mesh screen on the end of the dip tube in the gas tank was clogging up with a small piece of what looked like a plastic bag .Removed the dip tube and the screen.Now the fuel/water separator will pickup anything but won’t shut motor down.

I’d bet that plastic bag was varnish from old gas.

 

[edhorv59]

Thanks for the responses. I did check/replace the fuel filter separator, replaced the fuel pick up tube, used a 5 gallon can directly - all to no avail. It is a 2001 4.3L gen+ motor with electronic ignition (Thunderbolt V). removed the top of the carb a couple times and checked/readjusted the float height. Not sue how to check the carb for proper operation other than watch the acceleration jets squirt...

 

[Bondo]

removed the top of the carb a couple times and checked/readjusted the float height. Not sue how to check the carb for proper operation other than watch the acceleration jets squirt...

Ayuh,..... Welcome Aboard,...... Sounds like the carb needs a full on rebuild,.....

 

[alldodge]

Probably should have asked for the serial number, but does it have a TKS carb?

Float level 14 mm (.550 in)
Float Drop 27.4 mm (1.080 in.)

NOTE: Measurement taken from gasket.
NOTE: All measurements are +/· 1/64 in. (0.4 mm) unless otherwise listed
NOTE: Float level measurements are ±0.059 inches. Float drop measurements are +/- 0.075 inch

 

[ajent]

Pull the screen out of the carburetor fuel inlet port, and take a test drive. I've seen more than one coated in a layer of varnish slime that looks fine, but not even an air blower can clean the gunk out of it.