I have a twin ring Ryobi 31 without the compression relief slots. Should be pretty tight. It's a brand new engine.

I'm using 40:1 chainsaw oil in it with a 3-blade Master Airscrew 16-8 prop. Getting right at 6000RPM--maybe 6200RPM. The tach fluctuates a bit.

I had a Top FLite 18-10 on it and got about 5200RPM from it.

It has a Zama carb. Stock carb--couldn't tell ya what size it is.

What kind of RPM should I expect out of it?

Does anyone know the biggest carb I can put on it? I used to know a Walbro number--but I'm getting old. Seamed like it was a WT438 or a WT 343--something like that. It has the same opening as the hole in the backplate of the engine.

Do you think it'll get stronger as it gets some time on it?

Thanks