1990 30HP Revs HI and lo under power

[Austin Runner]

My 30hp was unused for a year. One pull start and idles fine. Revs fine initially under power but after a short time it begins to rev up and down repeatedly. It will run ok just above idle. Originally suspected fuel but changing gas, fuel tank, fuel hose does not change symptoms. Pumping bulb does not help. Fuel filter appears totally fine. Carb inspection showed no problems with all passages open. Changed spark plugs too without change of symptoms. Electrical connections appear uncorroded. What did I miss?

Thanks, Randy.

 

[reload]

Re: 1990 30HP Revs HI and lo under power

I think you missed something fuel related, most likely carb.

 

[grid]

Re: 1990 30HP Revs HI and lo under power

I'm guessing a piece of trash in the bowl that disappears when you flip the carb upside down to remove the bowl. Try holding the carb in its normal upright position and then removing the bowl. There should be something floating around, partially blocking the main jet.

 

[Austin Runner]

Re: 1990 30HP Revs HI and lo under power

Thanks Reload and Grid. I am looking forward to rechecking the carb for previously undetected gradeau!! Thanks.

 

[Austin Runner]

Re: 1990 30HP Revs HI and lo under power

Sure enough, removing the carb and keeping the bowl in its operating position showed up some deposits at the bottom. Not much but I guess it doesn't take much. I have ordered a manual and online subscription after reading several suggestions to others. I am also considering ordering a carb kit but this might be overkill. I'm just not sure.