So here is an interesting ? I purchased a used yet nearly new LRP .28 spec engine for my Matrix Arena! It has been broken in on 30% (10 Tanks). I only have and use 20% at my disposal. can I just put 20% in and begin running and retune??? OR is there another answer.
THANKS!

Just use the 20% and tune. You should be fine. The only thing that comes to mind, is if you can, see if he shimmed for 30%

THANKS! And if he did shim for 30%? De shim???

Yes .. if he added to lower compression for 30%

Can't you just use a hotter glow plug?