30hp mariner Engine surging

[Captmn]

Hi, I'm looking for some advise for a surging issue. I recently rebuilt the carb and replaced the fuel pump, gas tank ( with fresh fuel) and fuel line to my 1985 Mariner 30 hp. The engine idles well and runs fine until about 3/4 throttle then it starts to surge. Tank is the new EPA regulated non vent screw type. There's a vacuum build up that i understand is normal. I've cracked open the cap to prevent that but the boat still has the same problem. Could this be a vacuum problem somewhere in the system or perhaps an improperly adjusted high speed mixture setting?

Thanks in advance for your advice
Steve

 

[minuteman62-64]

Re: 30hp mariner Engine surging

I thought the new EPA compliant tanks have a one way vent that allowed air in but do not allow fuel vapors out? So there could be a pressure build up, not a vacuum build up?

 

[Captmn]

Re: 30hp mariner Engine surging

I thought the new EPA compliant tanks have a one way vent that allowed air in but do not allow fuel vapors out? So there could be a pressure build up, not a vacuum build up?

The tank I have does have a vacuum but I thought I read this this can occurr. I loosen the cap to overcome it but it does not solve my problem.