78 Mercury 7.5 thunderbolt

[Muskieman]

I have a 7.5 horsepower mercury outboard that has been driving me crazy and I need help. I love this motor but lately it's been surging alot at all rpm ranges. I tried everything ,changed fuel, cleaned carb, checked spark,changed plugs, and it still surges can anyone guide me on where to look next. It will do this for a couple of weeks and then stop for a while. I do think it gets better when I remove and clean bowl, although I don't think its good enough. I almost think it is sucking air but I don't know from where or if I'm on the right track thinking that way. PLEASE HELP!!

 

[Laddies]

Re: 78 Mercury 7.5 thunderbolt

It sounds like a check valve in the fuel pump is acting up. Have you replaced the diaphrams and check valves yet

 

[Muskieman]

Re: 78 Mercury 7.5 thunderbolt

No I Haven't does this sound more like a pump or a mixture problem

 

[Laddies]

Re: 78 Mercury 7.5 thunderbolt

With you having to pump the bulb to keep it running its the pump

 

[Muskieman]

Re: 78 Mercury 7.5 thunderbolt

Thank you for the info I will try fixing that next. Although It will stay running without priming as I run it. It just surges and really runs rough.