1987 4.3 litre intermittent rev increase

[Evinrude Boater]

My engine revs increase intermittently under load at any throttle setting. It seems the power is low most of the time and is normal when it revs up. Plugs are uniformly normal, new gas in the tank. Could an old water separator cause this? Any troubleshooting suggestions?

 

[alldodge]

Being a 1987 I'll assume carb
I would look at fuel pressure 3-7 psi. If that is good, then get back into the carb, but think you have a pressure issue (pump or restriction)

 

[dan2744]

I'd look at the carb too and make sure its opening correctly. A seperator could cause it if its dirty, might as well replace it to make sure. Fuel pump pressure low, clogged screen at carb possibly.

 

[Bondo]

Could an old water separator cause this? Any troubleshooting suggestions?

Ayuh,...... Especially if it's fulla water, 'n crud,..... It should be done at least once a year,.....

When ya pull it, Examine it's Contents for anything but clean fresh gasoline,.....

 

[Evinrude Boater]

Thanks for the advice. Rain rolling in so I’ll be a few days before I get back in the engine bay.

 

[Howard Sterndrive]

slipping prop hub?

 

[Evinrude Boater]

Changed the thermostat and fuel filter/water separator and fired it up. It starts right up with two pumps of the accelerator. It warms up but doesn't run smoothly and after warmed up it was hesitating slightly while idling at the dock. I didn't even bother to take it out for a run.

 

[Bondo]

Changed the thermostat and fuel filter/water separator

Ayuh,...... 'n what did you find inside the ole fuel filter,..??..??

 

[Evinrude Boater]

Ayuh,...... 'n what did you find inside the ole fuel filter,..??..??

The fuel filter/separator contents looked good. The center contact in the distributor cap was worn down so I replaced it along with the rotor and it still stumbled. Took the top off the carb and cleaned the orifices and it's running normal again. I guess 10 years of sucking dust catches up with ya.

 

[Scott Danforth]

has nothing to do with dust, that wouldnt ever get to the fuel side of a carb.

it has to do with the breakdown of fuel and the junk you pump into your tank

fuel systems need to be cleaned, no mater if its a carb or injector, fuel system deposits from degradation of fuel happen