My 8n has been running great till I tried to bush hog the other day. Under load it runs slightly rough and backfires through the exhaust. I also noted the same backfire and slightly rough running at 3/4 thottle (no load). I pulled the plugs and they look fine. It is a front mount distrubtor and I don't know how to get it off to replace the points, have to buy a manual. Anybody have any other idea besides points or condenser?