I have a 1997 yz 125. the cylinder compression is between 115 and 120. plenty of gas, spark, and air, but wont start. it also backfires about every 8 to 10 kicks. I know the compression is a little low, but is it to low to make it fire?
2 stroke bike are very dependent on compression. and being a bike that is 12 years old my best educated guess is that the top end needs to be rebuilt. i usually have to have the top end done on my honda about every three years.
Check your reed cage assembly, if i back fires means the reeds arn't doing there job
Rebuild it, compression should be 155-160 at least. backfires and hard starting is a common problem with compression as low as yours.
Have a look at your power valves my bikes power valve pins broke and the power valve went into the piston and smashed the piston and power valves
No matter how new i think my plugs are in my 2 stroke bikes, i always replace them first in my troubleshooting sequence. never had much luck with NGK plugs. these would show a good spark (when grounded to the cylinder), but its just not enough for light it off. change the plug and see if that works.
also, if you try to start it and immediately pull the plugs, are they wet? if so, then gas mixture to the cylinder is good, just no spark to light it off.
good luck.
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