Scota4570

I converted one the Craftsman 32 cc engines I have. It is simmilar to a Ryobi. I like the layout. I was thinking of making a WAL seaplane with two of these engines. This engine runs nice and smooth and hand sarts easily.
Unfortunately, it is a dog. 18x10 prop is getting only 6400 rpm. Really small props like 15x8 don't gain the rpms that they should, in my opinion.

I am using a carb intended for a DLE 30. I kept the flywheel but turned off most of the cooling fins. I bent the reed valve stop up a little. Removing the muffler only gains 200 RPM. The exhaust port is open for 126-degrees of rotation.

Should I open up the top of the exhaust port a little?

Is there a design feature/flaw of these engines that prevents decent power being made?

HunkaJunk

6400 doesn't seem bad for a 32cc gasser to me, I'm not sure if it could be considered a design flaw, but rather the engine was designed for a different purpose, you could try going up in prop size and see if your RPMs drop as you expect, as an example, I have a 98CC conversion out of a 2 stroke snow thrower, it runs about 6500 RPM, but it will happily swing quite a large propeller, the engine was designed for a higher torque application.

A limiting factor may also be how efficiently the fuel/air mixture gets from the crankcase into the combustion chamber, check the transfer ports for casting ridges and bad angles that will mess with the fuel flow. There are many Youtube tutorials on port tuning and polishing.

av8tor1977

My Feedback: (6)

That is a quite low exhaust port timing. Some of the Ryobi 31cc engines that are similar to the Craftsman 32cc also have a very low port timing. Raising the top of the exhaust port until you get a 150 degree port timing should make a nice power improvement. With better exhaust port timing you will probably notice that a larger muffler outlet on a gutted muffler will work better.

Did you get my PM about the Stihl 65cc Four Mix engines that I have?

AV8TOR

Scota4570

av8tor1977, check your PM's

Regarding the Craftsman. Since I got a bunch of the them I decided to mess with the ports. Before I started the exhaust duration was about 125. The transfer ports were 90. I crudely opened up the exhaust to 160 and raised the transfers to 140. It spins up a 16x8 to over 8K. The 18x10 goes no faster. The small prop is a lot faster. The thing is is doesn't idle well and is tough to keep running smoothly.

The tops of original transfer ports are at 90" to the side of the jug. That seems like it would not flow well. Even so, I put a fresh jug on it with a matching low time piston, it runs smooth again.

av8tor1977

My Feedback: (6)

160 on the exhaust is a touch too high unless you are going to run over 8000 rpms. And the transfer ports are tricky. They usually have upwards and sideways angles built into them that are critical to maintain, and the transfer ports have to open at exactly the same time too. I have many times successfully changed transfer port timing, but in most cases I just leave them alone because they are a pain to mess with.

AV8TOR

mmattockx

Flow is not the issue there, trapping the maximum amount of the intake charge in the cylinder is. Those ports are designed to aim the incoming charge to a specific spot in the cylinder in order the keep it from flowing straight out the exhaust port and hurting BMEP. If you don't have good info on how to reshape the transfers you are better off just leaving them as the OEM designed and tweaking the timing to suit.


Mark