I've discovered what I believe to be the cause for the rpm discrepancies between the 25 and 30cc Homelites. I stripped down my 30cc and converted it back to 25cc last night and while doing so carefully examined the ports. While the intake ports look similar in size/shape/timing the 30cc has a very late exhaust port opening when compared to the 25cc. It looks like I could port that but as the exhaust port is angled rather steeply I need to research it some more.

Can anyone provide me with some good port timings that they have used for a 30cc Homelite? I'd prefer something proven that can have a prop size and rpm measurement provided.

Also, can anyone recommend a good site that explains how to measure the port timing? I understand the concept but as I've never done it before it would be best to review the correct technique.