I finally ran a Mac 32 cc that I have been modifying. Didn't go all the way to the specs that BME (Keith) posted in the "Don't forget Echo" since I really wasn't trying to get above 8k rpm.

When I started, there was 65tho clearance between the piston and the top of the cylinder without the gasket. I cut 45 thou off the base leaving a clearance of 20 thou, but didn't reshape the top of the piston. I raised the exhaust port to maintain the 105 deg ATDC and cut the piston skirt to give an intake opening of 108 deg ABDC. I did bevel the piston where the ports open 20 thou to keep some of the port area lost when I cut down the cylinder base.
I'm quite pleased with the results.

MA plastic 18 X 6 8400 rpm
Bambuls 18 X 8 8100 rpm
Zinger 18 X 10 7800 rpm

What did you use for a carburetor and exhaust?

Thanks,
av8tor

Muffler is a Bennet from an old ST 3000. The Carb is a Walbro WA 19A. Ignition is CH-Syncrospark set at 30 deg BTDC. Picture attached.

Another picture

Not sure what it is, but sure don't look like any Mac 32 Ive seen.

I assumed that it was a Mac based on the similarities to a Mac 25 cc I got from CH about 3 years ago. The crankcase is identical to the 25 and the crankshaft is identical. I got it from a string trimmer that was several years old and don't remember the brand. The cylinder base has the mark M470 on it.
It has a bore of 1.496 and a stroke of 1.1 which is 31.68 cc.

If it isn't a Mac then I have no idea what it might be. It appears that the liner in the cylinder is nicasil, but I'm not sure.

Sure looks a lot like an Echo/Kioritz.....

AV8TOR

isn't that the little motor they put in that little bmw car with the door in the front .

just kiding it is a fs91 stihl engine, I have a couple of them myself.they advertised them as a 30cc engine,stripped it weighs 39 oz. good numbers thou.

Darin

It does look very similar to the Echo/Kioritz 25cc's I have, except most of mine don't have enough of a front crankcase extension to mount a ring hose clamp for the hall sensor. Plus the intake flange looks a little different as well.

Those numbers are way better than any of my 25cc's.

To be able to mount the sensor, I turned the front of the case till I had about a 3/16" wide stub. I then turned a ring out of Al to match the case and OD to the hub and used JB weld to hold the ring in place. This gave me enough to be able to mount the sensor. I have done a couple of other engines that way and have never had a problem with it coming loose.

I have the same string trimmer. I was able to get everything off of the block, except the clutch/pullstart. How exactly does this come off?

Dosen't the plug come out the top on a 32?
I just sold one that Terry had worked on and it didn't look like that..
It's was a screamer though...