I'm converting a Ryobi 26cc 4-cycle long shaft using parts from www.carrprecision.com. I'm planning on using it in a biplane of roughly quarter scale (12lbs, 72" span, 20x10 prop). I figure the low power-to-weight of a wacker engine would complement the short nose moments of the WWI era. The 4-stroke sound should add some scale realism to the fun, as well.

I've begun bench testing the engine to see if it is worth the effort of building the plane. The engine is stock (carb, muffler, magneto ignition). My main concern is the idle speed, it wouldn't reliably idle below about 2800 rpm, which translates to 25mph for the 20x10 prop. This is well above the stall speed for the intended bipe, so landings are going to be too hot.

BTW: I took off the muffler for one run just to see how loud it would be. There was almost no difference in noise at idle!!! However, the idle speed shot up to about 3500rpm. The idle adjust screw ran out of range and killed the engine at around 3000rpm.

Are these results typical for this engine? Will a CDI ignition improve idle? Or, is it better to leave the flywheel weight of the magneto ignition?