The porcelain cone of the dissected spark plug does not show any detonation that I can see, The operating temperature of the porcelain cone is too cold. I do not know if that is because the heat range is too cold or the combustion temperatures are not in the range where they should be when an engine is making close to maximum power. You have cut off the most important part of the spark plug that tells experienced tuners about the heat range and combustion temperature. Please do not destroy any more good spark plugs trying to find the optimum jetting. Please read this link. http://trx250r.org/threads/7326-More-power=67051&viewfull=1#post67051 I hope that it will prevent you from becoming another victim of another one of the very popular internet myths that are causing novice tuners to destroy pistons when trying to tune their engines using the spark plug dissection approach to jetting.
Show me the top of the piston. I can tell you much more about where you are in your search for the main jet that will give you the highest power and whether your piston temperature is knocking on deaths door.
Coolant temperature has very little to do with burning a piston unless the engine package was not well designed and tested. A well designed package will not be driven into detonation with 175 deg coolant temps. A poorly designed package can experience detonation when coolant temps are at room temperature. A hole will not burn in the center of the top of the piston or burn off the edge of the piston on the exhaust port side unless the engine is experiencing detonation.
Detonation will raise it's ugly head when one or more of the following conditions exist:
1. The engine is too lean.
2. The ignition timing is too advanced.
3. The cylinder head design does not match the rest of the engine package.
4. The exhaust pipe design does not match the rest of the engine package.
5. The exhaust pipe discharge path has too much restriction.
6. The fuel's octane rating is below what the engine package requires. You will never cause an engine to experience detonation by using fuel that has a higher octane rating than what the engine package requires.
This is the first plug I've ever cut because I keep reading to look at the base of porcelain.. I normally just look at the electrode. My complete engine was built new by Pete @ Hybrid Engineering so I'm assuming all is up to par. I started by dialing in the air screw pilot and needle which feels great but it always seemed very sluggish up top with a 200 main. I couldn't even pull the front end off the ground in 3rd or 4th gear and it felt sputtery so I dropped it to a 190 and that's where I'm Sitting now. The bike has woken up tons and feels great! Now she will stand up in 5th and the power comes on smooth all the way through.. The plug on the left is after 30 min hard ride with 190 main and the plug on the right is same jetting but with a 200 main.
Thea other pics are all of the 190 plug
Here is my piston after 14 hrs of running with the 200 main jet
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