D
Deleted member 12676
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The temperature it take to ignite gasoline is 495F. The hottest a two stroke cylinder head should get is 450 degrees continuous running, 500 for short periods. (see graph below) The picture below is of a motorized bicycle that caught on fire after the owner parked it after a ride and some gasoline dripped onto the cylinder head. What are factors contributing to a higher head temperature?
1. the stock Grubee CDI. It has way too much ignition advance at high rpm which causes engine overheating by combusting the mixture too early (and so causes more peak temperature and pressure).
2. a high compression cylinder head. The higher the compression, the hotter the engine. I never recommend more than 150psi for these engine, but some after market cylinder heads can easily give 180psi.
3. too lean an air/fuel ratio. Try different main jet sizes and use the size just bigger than the one that gives the highest top speed. The excess gasoline serves as coolant.
4. a cylinder head with a squish band. The band lessens the piston temperature (which lessens liklihood of seizing it) but raises the head temperature. I measured a 50 degree difference when I tested heads back to back.
People who have had cracked cylinder heads probably didnt even know their engine was overheating. They just went and bought another head to replace it.
1. the stock Grubee CDI. It has way too much ignition advance at high rpm which causes engine overheating by combusting the mixture too early (and so causes more peak temperature and pressure).
2. a high compression cylinder head. The higher the compression, the hotter the engine. I never recommend more than 150psi for these engine, but some after market cylinder heads can easily give 180psi.
3. too lean an air/fuel ratio. Try different main jet sizes and use the size just bigger than the one that gives the highest top speed. The excess gasoline serves as coolant.
4. a cylinder head with a squish band. The band lessens the piston temperature (which lessens liklihood of seizing it) but raises the head temperature. I measured a 50 degree difference when I tested heads back to back.
People who have had cracked cylinder heads probably didnt even know their engine was overheating. They just went and bought another head to replace it.