ORIGINAL: Harry Lagman
Dar, in contrast to Tower's site, the manual says "For the best performance, a fuel containing 5% to 20% nitromethane is preferable". It also recommends three plugs: A5, A3 and #8.
Harry,
OS apparently does not!
Since the manual that you have was written, OS has updated its home web site.
Please read [link=http://www.os-engines.co.jp/english/line_up/plug/pluindex.htm]this web page[/link].
The only aero engines, for which the A3 glow-plug is recommended are LA engines up to .40 and all smaller than .32 engines.
The .50SX does not fit into this selection and the A3 is for sure too hot for it.
The OS #8 is the only plug that does fit the bill.
The same web page says the A5 is for .61 and larger engines.
The shortcomings of the .40FX-.91FX manual immediately come into a demeaning view.
The A3 is apparently not recommended by OS for any of the above engines, but in the manual it appears...
The fuel recommendation of up to 15% nitro is indeed from Tower.
And it is not institutionalization I am after, but optimization.
Using the right fuel and the right glow-plug, will give you the best performance and the least fuel waste.
Aren't we all trying to make this hobby more affordable?
Just wasting more expensive fuel and more of it, is just putting us all in reverse.