92 Johnson 40 Surging at 50%+ RPM

[lowepontoon20]

To make a long story short: I bought a pontoon with a 92 Johnson 40. The motor was running great when I bought it. My buddy owned it and I used it at his place all weekend before I brought it home. I filled it up (I'm about 50% sure I accidentally put ethanol gas in it), and no start. Cranked it about 50 times and couldn't get it to start at all. I checked spark and replaced both plugs, fuel flow, replaced the prime ball and fuel line, checked oil flow from the oil tank and pressure on the oil prime ball, all good. Finally when I went to use my chainsaw I mixed gas from the same fill and it wouldn't run at all... finally figured out I had bad gas all along. I went and got 91 non-oxy and ran the motor off of the gas can.

So now, the motor will start great, idle perfectly, and run, however in both forward and reverse it will start surging/cutting out at about 50% throttle. I thought the in-line fuel filter might be clogged so I replaced that and it still does it. The fuel prime ball is staying hard and if i back off when it starts surging it'll run perfectly again. Any suggestions?

Thanks in advance!

 

[Spartans]

If it was working before and not know it Sounds like an air leak on a fuel line. Try easiest stuff first and swap out tank and hose with a known good one and test to see

 

[juno pierrat]

if you got a really bad bunch of gas, say water, remove air intake, and drain carbs, try again, easy ,if no help then take carbs off for cleaning insuring all small passages are open

 

[He rik]

Done that on a motorcycel(2-stroke), bad gas, had to clean the carbs and it was like yello inside.

Something happends when the fuel got in the carbs, my friends injected bike run fine on same filling so I just cleaned the carbs and tried again with the same result, new fuel and cleaned again and it run.

But check the easy stuff first as mentioned above.