I am running engines converted from RC.  I have 

OS25LA with the e-2030 muffler, APC 9x4 prop

and

OS20FP with the e-2030 muffler APC 9x4 prop.  These are the older iron sleeved engines if it matters.

I am running Omega 10% or 15% with added castor to a total oil load of around 22%. 

Since these are used engines, and RC conversions I am unsure what the glow plug is supposed to be (I am unsure what plug is in them right this instant, but they are in the garage).  I have OS #8 plugs on hand.  I have run these engines with what they have in them as minimal cleaning was needed on any of them and they ran fine on the ground on the fuel I have.

Thank you

Phil

   It is absolutely critical to run the *stock muffler* - it is absolutely key to the way it runs well for stunt. And it should be completely unmodified, nothing changed in any way. IT runs enough better that way to make up for any minor weight increase, at least on airplanes that are of appropriate size (35-sized).

    I haven't found the glow plug to be critical. The 25LA-S comes with an OS #6 and that seems entirely satisfactory, but I have run discarded Thunderbolt 4-Cycle plugs from my real airplane with the element scraped clean and old Glo-Devil #300s.

      The stock engine (highly recommended) wants at 10% nitro for good needling. It will run OK on 5% but is touchy on the needle. 15 or 20% (like YS 20/20) smooths it out more, and above that, you don't really gain anything, up to 35%, which is the most I have tried.

     Brett