Originally Posted by
AeroFinn
It' seems the "old school" approach is to partly compensate inadequate cooling by having excess amount of oil in the fuel which is then thrown out of the exhaust to cool down the otherwise too hot running engine.
I think excess oil is also to compensate for the volatile ignition timing W/GI.
When GI is used, the A/F ratio will affect ignition timing resulting in a "double whammy" as far as detonation. Leaner mixture raises the combustion chamber temperature which leads to detonation, the ignition timing advances exaserbating the detonation conditions. I see the excess lube as an deterrent to pre-ignition as well as a coolant due to extra lubrication that might save an engine running lean on GI.
It would not surprise me to see 0% nitro, 10% lube W/CDI making power similar to GI W/10 or perhaps even 15% nitro and higher 16-20% lube content.
BTW, if you play with the ignition timing, make a "witness mark" on the prop drive hub and magnet ring for reference. Another 4-5° of advance will probably give you another 150-250 RpPM. Maybe not, but you should give it a try. I have never had any difference in idle/transition between 28 to 35° total advance. Even @ 35°, the timing is pulled back to 10° BTDC for starting & low/midrange. W/the slower flame propagation of methanol, it doesn't seem to affect the low end manners.
Still the FA-125 does seem to be the "odd duck" so YMMV.