Actually it is the poor mans way to increase port timing. Think about it the skirt gets out of the way sooner and closes later, increase of time open. When we were kids we had no way to port but we had a hacksaw so you guessed it we used the saw. I would not recommend it, the pistons were cheep and we had all the time in the world, ours was an experiment and the porting was better on those Hodaka's. The happy time has gotten better in the last few years, I got an engine from Dax and the exhaust was right on 1.1" from the top. I never match ports on these engines they just run too slow in my judgment to warrant the extra work. I do look to see if I can find a thick gasket to insulate the carb though. I have never used an expansion chamber yet, and that was a must for our bikes back in the day, I guess the reason is that my bikes will pull from any stop without my having to pedal so what is the need! Also I am running a 39 tooth sprocket. I have a Whizzer now and the happy will still out pull and climb the Whiz. The Whiz has a higher top speed but I never go that fast. Have fun, Dave
PS:This is a barrel off a Honda CR 250, Look at the exhaust ports and how they go over the Scavenging ports! I would think that the charge would just go out the port.