Does anyone have the same problem?

I am using the NMP header, Johnson pipe, Magnum DZ fuel (I believe 23% oil, 30% nitro) on my 140 / 160 DZ, I am having the toughest time keeping the engine from carbon build up. After about 20 flights, the header is full of carbon. I ended up sending the engine back to YS for de-carbonization almost after every 50 flights, even Richard Verano was puzzled with my problem.

Is my engine running too rich, pipe too constricted, temperature too high, too much oil and nitro, or a combination of all?

Any suggestion is greatly appreciated.

Thanks in advance.

Adrian