i cant even find a techwell .12 on the net. i havent seen one nor have i heard of them before. i fyou are running a std threaded crank with a pull start ? then i would suggest an OS 12cvrx, they are a littlebit more in price but believe me its worth the bit extra. the quality of the motor would be better and being a direct fit for a threaded crank and pullstart, they put out nearly 1hp, reliable and easy to tune and they hold their tune. if you have a bit extra dough, then i would spend it on a better engine. i am going through the same thing at the moment and maybe i should have spent the cash to start with in the beginning.
Serpent - Walter RC
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