Hi Guys,
I bought a brand new weed wacker Honda 31GX 4-stroke engine. After removing all unnecessary stuff it weights ca 1.7 kgs.
This is my first petrol engine and I want to try its abilities in an old Extra 300 which had Super Tigre 3250 before . I don't expect
any aerobatic performance from Honda, but just curious how it behaves in the air. If OK , may be in the future I will put it to some big Cub. Which prop should I use for it? Thanks.

You are going to need a "four stroke" carb with both a high and low speed needle to use the engine in an airplane

Walbro WT-456-1

Thanks. Sorry for my message wrong location.
How this engine will behave in the air with its original carb?
Which prop size would you suggest?

Why would this be necessary? I have two of these engines, well one is still in my wife's rototiller, the other on the workbench with the BS cut off, but they run great. I'd like to know what prop to run also, I'm planing to have it in a D-VII.

18 X 6

http://www.rcuniverse.com/forum/m_7168058/tm.htm

Thanks, lots of good info in that thread.

Thank you w8ye. It is agreat Honda thread indeed.

I think the Honda GX-31 is the better of the four strokes

I've flown mine for years in a GP Stearmen...Original carb and swinging an 18x8 at 6400 rpm with a straight exhaust. The sound is great and still very quiet. One of the most trouble free engines I own. A terrific engine for those guys that can't keep there hands off the carb needles!