RE: os fs 52s
Gary, you might try replacing the fuel lines. I was filling mine a couple weeks back and I saw what looked like a spider web floating in the engine compartment. When I stopped the pump, it went away. When I started the pump again, it came back. I had a pin hole in the line. This screws up the mix a bit. Also, you may smear some vasiline around the intake manifold to carb joint, along with around the needle valves. This will show up a bad/leaking Oring that needs replacing. Last, try a fresh OS Type F plug. One of the guys at the field used to be tech support for Novel and he said that some types of contamination will damage the glow plugs to the point of not providing low end reliability. Personaly, I've never seen a glow plug that was defective that glowed when the battery was applied. At least not that I could tell. I am not an expert here though.
I run the APC Sport 12 1/4 x 3 3/4 props and they work well. With the trainer, after two flights, they were usually 11 1/2 x 3 3/4 though. They pull well and you can run the idle a bit faster and not overpower on landing. You will not get as much top end, but if that is what you are after, you need a 2 stroke. I also ran 12x6 props for a while. I don't really think that a different prop will make a difference, not one that is in the power range of the motor.
Did you check the valve lash? It also may be causing a little roughness.
Oh yes, one more question, are you running the engine inverted? Idle there can be a problem and an onboard glow power may be needed.
One more question, how slow can you get it to idle without shaking, even with a slow response to high end.
Another idea just popped into mind. Turn in both needle valves to stop, don't force, and count the turns needed as accuratly as you can. Now remove them. Put an extention on the pressure line to the tank and blow into the tank. It shouldn't take much to get fuel blowing out of the high speed needle valve hole and out the carb mouth. A bit of contamination may be getting into the lines and needle valves causing an uneven supply of fuel. I run a fuel filter on both the pressure and supply lines. I've take a tank out of a plane after just a gallon of fuel and there will be a big black ring where the pressure line is pointing in the tank. Filtering out any crud that can get to the needle valve will only help.
Let me know how it goes.
Don