Does the motor use oil ? It looks more like oil fouled than fuel fouled. You are fully correct, if it was over rich in gas, it would actually be opposite in hard starting issue, easier to start cold, but hard to start once hot. I had one messed up carb that made the bike miss and run real bad, any hard throttle and black smoke blew out the exhaust, still the plug never fouled, it takes a lot of gas to do that, enough to be very bad running at all times that you would have noticed.
You need to check the spark condition, is it a sharp, big blue spark or tiny weak orange. Then a compression check and leak down test to see where any comp loss is from. Valve clearance should also be verified correct if any concerns about previous work.
I suspect weak spark topped with some oil burning. Ignition coil may be weak or a poor grounding of the motor. Can you get an Iradium plug to try? I use Denso IX24B , splug fouling issues and weak spark is where iradium plugs are a big help , otherwise not a real benifit for the cost.
.
|