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I followed Shannon's suggestion and set the points to open/close at 0.17" BTDC. Both of Dave's engines are set that way and they start well and run quite smoothly.
I have one of my engines set at 0.15" and the other one at 0.17". The set to 0.17 had 100 RPM more than the one set to 0.15". The Left one is 0.15" and when I measured it last year it ran 5600 RPM static with the biprops. The Right engine is set to 0.17" and it will turn 5700 RPM static with a biprop. I find that the right engine idles rougher than the left engine. Every thing else being equal, which they are not, I'll explain later, I would expect higher RPMs with the 0.17" setting providing you do not get knocking, Predetonation.
To further complicate the experiment the right engine has the spinner backplate but no spinner. The left engine has neither the spinner nor the spinner backplate. The carb on the right runs a little richer at times even though I try to set them for max -1/4 turn The pump works better on the right engine. I need to do some maintenance on the Left pump/carb
Both engines run well enough that I did a 140 mile crosscountry on Saturday and they ran like swiss watches.
My 2 cents worth, Bill

Thats great Bill, and thanks for some hard numbers confirming your settings and rpm.

Looks like the Magic number is about 0.16" BTDC.

Its good to know how reliable those little devils are, given a bit of TLC and a fighting chance.


About that Xcountry, was that on a single tank of fuel?
Where did you go?
Any pics from the trip?