Also to consider: You must richen the needle valve before each start and then lean the engine to peak RPM. USE A TACH! You cannot run the engine and "trombone" the pipe to find the proper length. You must start the engine, set the needle, and tach it. Then you can decide if you want to shorten the header. Shorten it in 1/4" amounts. When you have no RPM change, lengthen the pipe by 1/4" (you'll make the gap in the silicone tube a bit larger), and fly the system.

Listen very carefully to how it's running in the air to make sure you have the pipe and needle set correctly.

If the pipe is too long, the engine will trend rich. If it's too short, it will trend lean and could cause detonation, damage to the glow plug, or even burn a hole in the piston. Yes, we've seen the results of a too-short pipe coupled with detonation!