88 marathon occasional backfire and fouling plugs.

[06dvx]

So I bought a '88 marathon and it seemed to run good when I test drove it but that was last fall. Now it's fouling plugs and has an intermittent backfire. Have searched many forums and have fixed up a few things from reading those.
I have put in a new spark plug(bpr4hs), changed the fuel and made sure was correct 128:1 mixture. Replaced the spring on the throttle as it was missing and adjusted the micro switch to click before the throttle moves. It does drive 100X's better but still has the occasional backfire and fouls the plug after about 1/2hr of use. I also went over the intake to make sure there is no leaks. I'm a 4 stroke guy and no experience with 2 strokes unfortunately. The cart was to be used for transportation around our subdivision when it's nice out. Hoping you guys might have some other things for me too check. I also find this motor to be louder than any others that I have heard and drove and not exhaust loud. It's also a lot faster than any other cart I have driven. Thanks in advance guys!! Been a Lerker here for a couple weeks before registering and tons of great info here!!
Oh as a side note located up in Edmonton, Alberta, Canada. 2200ft above sea level. Hopefully BPR4HS is the right plug as thats what I took out of it.

[cart around]

The intermittent backfire might be from the plug fouling out.

You might want to start with checking the fuel pump. http://www.buggiesgonewild.com/gas-e...fuel-pump.html

[06dvx]

Thanks for the reply. I will look into it. Good read for sure ��