RE: OS 33GT Gasoline Engine for Pattern
Around 28" from center of piston to the main reflector should be just right. 1" longer won't hurt but shorter might, depending on the pipe design.
A Walbro with a barrel type carbcould help and I'd like to try it. I didn't think Walbro made oneso I have not checked. Athird needle for mid rangeshould also help but that requires a new carb design altogether. Either that orinstall an arm on the low speed needle and set it up on a servo...
The standard Walbro that comes with the OS33 is not that bad really. Very manageable with a rather flat curve from 15% to 80% of stick travel. This middle 65% of stick travel causes about 35% servo response. The jump at around 4K rpm is lowest with the OS, possibly due to conservative exhaust timing.
A couple years ago before theOS was available,I was running the SAP180HP and have a 60 page threadhere in the Pattern Forum on what we learned. The jump at 4K with this one was very noticeable; manageable also but much more noticeable. Exhaust timing was around 170 degrees as I recall.