Originally Posted by JetMD

I did a little experimenting with this and what I found on my os tz .12 was that when I cut the small grooves in the head button, that gave me a decent increase in bottom end and didn't affect mileage. I tore the motor apart again and did some grinding on the crank opening and lowered the ports on the sleeve. I didn't feel any difference in power and it litterally killed my mileage. I went from about 5.5 min. to about 4.75 min. to a tank. I wasn't too happy about that. So, I put a stock sleeve in it and now it's my back-up motor.