I have converted several engines over the last like 4 years (ok, so only a handfull got finished) and know the Mac 28/32's are about 4.5lb, homies are around the same (assuming still on magneto), and I've stripped down a few featherlite engines, had a 18cc down to 2lb with prop for gas/glow but didn't realize that those things come in right at 3lb on magneto, that's pretty good considering.

I know everyone knows that the featherlites are low on power, but I'm sure that has something to do with the 115-120* exhaust timing, getting the timing up to 145-150 requires nearly doubling the port height, they start out about 5/32" high... I have two of the 21cc engines ready to go and will run them this weekend so I can sell them and see what kind of power they put out. I use the mufflers held on by springs, the older style aren't crimped together or anything and you can just remove the baffles, if the plane allows you don't have to make any fancy outlet, you are left with about a 1/2" outlet (I imagine about right for the 18cc), even the mufflers I added the 1/2" tube to that's like 3" long are only 3oz. I'll try to get some pictures up this weekend, I think they make fairly clean conversions.