Hey guys/gals
Recently I aquired a 1/4 scale J3 cub model, which I planned to use for glider tow. The plane had it's share of problems, I got it cheap, so took time to solve all.
Regarding the engine (58cc MVVS standard with side muffler), I never got it to run consistently, and was tweaking needles all the time.
Conditions:
rear carb
cowl extracts air in a slit between fuse and upper front deck
I have made a cooling duct to ectract the hot cooling air
Carb got hot, so I blocked air from side mufflet into the rear of cowl
Added cool air scoop louvres on cowl top

Still the needles were not consistent, and sometimes the engine went lean, and the other moment overly rich, with differences in ground handling and flight.
So I planned a few cures like:
- reference pressure into the fuselage
- using balsa box system

To be continued