I started my first conversion on a Homelite 25cc engine. This engine was in a Craftsman branded weedeater.
While working on this conversion I stopped by a local small engine shop and they gave two more weedeaters,
another Craftsman and an original Homelite. While they look very similar there are a few differences. The
major difference is a hole in the cylinder above the exhaust port of both Craftsman branded engines. The
Homelite, which is older, doesn't have the hole. The whole is even in the muffler on the Craftsman engines.
In the photos the Craftsman parts are on the left and the Homelite parts are on the right.

Is this some sort of emissions thing? And does it rob power? Can I plug it with JB Weld?

John

Yes it is an EGR device

Plug it with a very short set screw but be careful and not run the tap into the cylinder wall. just make enough threads to get the shortest set screw flush

Thanks,
I'll do just that.

yes, also called a compression release which releives compression for ease of starting.

I found a 10-32 tap will cut nice threads with out drilling a pilot hole and a 1/2" screw is just right.

We don't want no stinking easy starting motors!

Yep, use a 10-32. A 8-32 will push through the cyl. wall pretty easy. Trust me.

Just finished my first Homey 25. With a lightened flywheel and some internal work it turned a classic 16/10 at 8100 rpm, 54 oz. Good Luck with yours. ProfG

The compression release was a valve above the carb on the other side of the cylinder. They were on electric start versions. It was bigger and was like 1/8" pipe thread.

The electric start carb insulator also mounted the carb at a better angle

profgigawatt,
Wow! Those are impressive numbers.

w8ye,
Yes, as I see it, 2 strokes are notorious for burning only part of the fuel/air mixture and dumping the rest out the exhaust. Really, it's the fuel/air mixture coming into the cylinder and out the exhaust port before the exhaust port closes on the up stroke. When the spark plug ignites the mixture in the cylinder, the piston moves down, then the small hole above the exhaust port lets hot gases into the muffler to facilitate burning of the unburned fuel/air mixture in the muffler. So no, it's not a compression release. Please correct me if I'm wrong.

Sounds good to me

The site rcfaq.com has an engine conversion page and on that page is a Homlite hopup spec. That is where I got the numbers to modify my engine. I have had a problem. When I removed the excess material on the front of the engine I removed the webbing also and had a clean lite case. I found that at the power I now have that I removed too much material. The webbing needs to stay on the front of the case. I have broken two cases at the main bearing boss. I can send a picture if you are interested. Profg

there a quite a few brushcutter engines that were fitted with this comp release hole on the exhaust port side, the idea of this is after TDC when the piston is just on its way down a small amount of compression is released before the piston opens the exhaust port. other types of cylinders dont have this small hole , they have a milled cut into the cylinder wall going from the exhaust port top and up about 10mm above this port. any holes fitted to the carby side are whats called Purge Pressure which is needed for carbys such as Walbros etc. otherwise they wont pump.