Re: Does this spark plug look good?
The photo is blurry but that sure looks like aluminum throw-off from the piston due to detonation.
The top cylinder of a pair usually runs slightly leaner than the bottom so on a pair of cylinders, if mixture is marginal, it is usually the top one that will first show damage. Check the setting on the carb (7/8 to 1 turn open preferred)and check to see that there is no clogging. Once you run a compression check, if compression is high, the engine is run-able once you correct the detonation. However, with that amount of aluminum throw-off, you will definitely want to replace the piston as a winter project. Reason: The crown of the piston is now rough and can trap deposits which MAY remain glowing and cause pre-ignition. Depending on the condition of the combustion chamber, you may also want to replace the head.
If the cylinder liner is not scored, the piston can be removed without tearing down the engine. Remove the carb and manifold and unbolt the con rod capscrews through the reed block opening. Push out the piston through the cylinder. Keep a rag under the reed block opening to catch any rollers that may fall out. Some of the rollers will drop into the crankcase but they have no where to go so you can fish them out with a piece of fine wire. Just be careful to not let any fall out the exhaust ports then you will probably not find them and then you will not be able to count them. Count them to be sure none are left in the engine. You need to retrieve 16.
It is a little tight to do it this way, and takes a little time, but it sure beats dis-assembling the engine. It is cheaper and easier this way but the negative is that if the cylinder is worn more than .002 over, you will lose a bit of performance.
