MrPcub and rcflyer.

I think you could get about any carb to work but would take some modification. I've been thinking about and working at this problem for about a year, off and on, and have come up with three solutions.

1. Leave the stock 9mm alum body WYL and bore out the main jet. I also took the needle sheath out and widened the narrow part of the taper ever so slightly to richen up the transition. I havent found a way to get the needle to move with out ruining the barrel assy.

2. Put on some sort of one-way check valve, like the stock one, but with a higher opening pressure to let some crankcase pressure build up before the valve opens to vent. This way you could drill/tap the crankcase and use + pressure pulses like two strokes. You would either have to build a custom carb spacer/pressure line to case or drill/solder in a pressure tap into the carb pump cover.

3. Use any two stroke carb and put in a diaphram return spring. I've tried this a couple times and can't get it to work as well as the stock pump setup. I tried to swap pumps but they are a different design from the two stroker's carb body. Also, the stock WYL has a flat spot milled into it to locate the spring and keep it perpendicular to the diaphram. I haven't tried to mill a flat spot in any other carb. I couldn't seem to find a spring with the same rate as the stock one. I also wasn't sure if it stayed upright while assembling the carb/pump.

Check out my last post on "ryobi 4-strokes, who's running them and what do you think?" thread. I rotated the carb barrel and gained 100 rpm. Also, turn the carb so the barrel linkage is facing up. Worth another 1000 on mine. Also, I posted jetting sizes and what effect they had.

I've read posts on RCU claiming people were running 22" props and getting over 5000 rpm. I don't believe it. With CH Ignition, dialed in jetting and a low restriction muffler I'm getting 5700 rpm with an APC 18-8W.

Oh, I flew my 14# Nosen Champ for 45+ minutes mostly 80%+ throttle on an OJ juice bottle(12 or 16oz????). Pretty fuel efficient.

Let us all know if you try anything and how it turns out. I'm still pondering an opposed twin. 52cc!!!

Doug