So I've got a strange little problem. I run a Grubee Skyhawk 48cc with a CNS carb and NGK B5HS plug gapped at .025, with a fuel/oil mix of 20:1. With my 48t sprocket I can usually get around 28mph on flat ground and climb the huge hill in front of my house at about 17mph (huge hill!). But lately, I'm doing good to get up to 20mph on the flats and can't climb the hill at all without pedaling. When I'm running WOT on flat ground, the engine sounds like it isn't getting up to full RPMs. I have no exhaust leak, but when I took the end off of the muffler there was a lot of oil laying in the bottom of it. I've taken the carb apart and cleaned it and the air filter, changed the fuel filter and out of desperation, tightened my head bolts. I found that they weren't loose to begin with, but I was afraid maybe the head gasket was leaking, not the case as far as I can tell. The plug is a little fowled, but I've had worse and it ran better. I was going to try a new plug anyway, but I thought I would ask around here first and see what you guys have to say.

I noticed a few other threads about engines with low power, but they seem to be different than my situation. Any help at all would be greatly appreciated.