88 spl surging,dropping rpms,then surging.

[73 Dolphin]

Took the boat out today for the first time in a year. I do start in up regularly out of the water.
I don't have an RPM gauge but it will top out at about 42 mph.
I was doing a sedate 25mph and after 20 or 30 mins the RPMs started surging. RPMs increasing and dropping without me moving the throttle.
Probably dropping to <20mph then surging to 35mph or there abouts then repeating.
Yes its old fuel. I know they don't like that.
Pumping the ball made no different and the ball did not collapse.
I will check for water in the fuel, compression, carbs leaks, spark plugs etc.
Is there something else if should be looking at?
Thanks.

 

[racerone]

Post the actual compression values here.----Test run with the cowling off and a timing light hooked up.----Test run one cylinder at a time.----Observe the flashing light.

 

[saltchuckmatt]

Are you running a nice spin on fuel filter?

 

[kd4pbs]

Water in fuel.

 

[Crosbyman]

flush the old gas and run a small tank with some engine cleaner ...maybe you can clear up some obstruction... if not a carb job may be in order. jmho

 

[airshot]

Once you said running on year old fuel, you answered your own question !