FPE 2.4 has Black stuff and oil in exhaust
I had the same problem with the 2.4 as well as a Brison 6.4 I called Harry at Brison he recommended Amsoil racing 2000 premix. It is recommended at 50 to 1 he said 64 to 1 which is 2 ozs per gallon runs great on that mixture and engine is very clean and no black stuff. He advised most modelers use way to much oil and to much oil can actually cause added heat and carbon build up. Also i always use High test fuel 92 octane it smells a little cleaner than regular.