Being that we are working with little engines that have no form of intake valve (reed or rotary) and no tuner pipes (well, for the most part, we are mainly talking work saws here) we are pretty limited on how aggressive we can go with the intake. If there were an intake valve of some kind that closes and traps that charge in the case the instant the piston starts moving downward rather than approaching closure of the intake port itself, we could really have some big power mills. Think about the HP a 125cc dirt bike makes compared to a 3120. Yeah there is more than just intake valves and tuner pipes involved, but it certainly plays a role I think. But I digress a bit and we have what we have.
I understand the intake enough to know that we don't want too much duration for fear of low case compression inevitably creating a slow and lazy transfer action as well as some loss of fuel atomization. But at the same time we want that case to get a good gulp of fuel/air too. All I can really say with confidence on this subject is that generally speaking most of us are looking at between 70 and 82 degrees BTDC plus or minus a degree or two for the most part. I can definitely understand why we need to be cautious not to give it too much intake duration. Besides freeporting, transfer is the first in line to suffer a loss in performance and efficiency. How to determine what is too much or how far one can take it, I do not yet fully know. Standing by to listen and learn.
