Airacobra

I realize this is an older engine but it's brand new and I want to use it. Does this engine have to have a velocity stack sticking outside the cowling to make it run well?

kmeyers

Wow, up for 2 days and no reply.
No, you will likely get better results without a stack sticking out (providing there is at least 1/2 inch clearance for the carb opening).
Changes in air speed past the stack unshielded can cause poor engine performance. I have a Zenoah 20 that lived in the airstream unprotected and worked great. I also had another 20cc (piston ported) that needed the carb protected from the airstream. go figure. Pressure in the cowl can effect both the venturi and the pressure regulator, go figure.
Bottom line is 80% of the time cowled and enough clearance is best (in my experience).

Truckracer

My Feedback: (19)

Kmyers advice is good as always. In many cases, the stack doesn’t improve performance but does help to keep the gas spray from the carb in the carb. This is common on piston ported engines. The engine will run fine with or without it.