About my suggestion to change the timing, I was thinking about another magneto with slots. I looked at the Toro just now, my suggestion is not that good for this engine, it would take some engineering to change the timing and who knows if the time would be well spent. I tend to be satisfied with 7500 to 8000 RPMs out of 25cc. I just read your comments about the 2 bbl version with not much metal around the ports to enlarge them. I think this is what I have and I was wondering when I read you saying you enlarged the ports a lot. That is now cleared up. I haven't had a whole lot of time either up to now to work on these Toros. There must be several versions of these engines, maybe some we haven't seen yet. I took the rear cover off of the rear intake, you know the little rascal where the rear rubber tube connects, to be absolutely clear. There is a Reed valve in there. Is that familiar? I didn't check the front one yet, but I expect it will have one also. With these particular engines, lets call them the "2 bbl light castings", I would think the exhaust ports could be enlarged a bit and then an adapter intake should be possible to use a bigger bore 2 needle Walbro or ZAMA carb with an adapter intake spacer that makes use of the rubber tubes to the front and rear intake ports. I will try something along this line of thinking when I get to it. These engines have turned into a tangent hobby. I have two RC airplanes, glo versions, and I haven't flown either one in a long time. You mentioned a 28cc McCulloch, the first engine I converted is a 32cc Mac. The ports are decent sized as is, I used a 5/8" Walbro and get close to 8000 RPMs with a 20-6 prop. Of course I added a 5/8" pipe to the muffler also. I like the 32cc Macs, I have a couple more of them, but they are around 5 lbs.