L185 surging

[teachingscience]

So since I last asked for help on My L185, I've got it starting very easliy and thought it was all good. I let it set and idle tonight and it surged like someone hit the foot throttle. It settle back down and then did it again. Any ideas???

Thanks in advance for all your great ideas.
Charlie

 

[North Idaho Wolfman]

Contaminated fuel is about the only thing that I know that will do that.