Tycho,


About the rotational 'free-play'; if you can rock the prop over a span of 35 degrees, without the piston moving down from TDC, this would indicate an accumulative clearance of 0.44 mm. if it is 40 degrees this accumulative clearance grows to 0.57 mm.

This is calculated by deducting the cosine of half the number of degrees (since 40 degrees is 20 either way), from 1 and multiplying the result by half the engine's stroke.

It is accumulative since it adds up the clearances of the rod bottom end on the crank-pin, the rod top end on the wrist-pin and the wrist-pin in the piston. If rear bearing slop is also in the issue...
(I know some might say I did not take the rod angularity factor into it, but this is a much smaller number, since the rod is over 3 times longer than half the stroke, so the cosines are much closer to 1.)

This amount of accumulative clearance, when taking into account the 5-6 mm diameters of the shafts involved, is excessive!

I would say 0.1 mm is the maximum you want per location, in a sport engine, or 0.3 mm for all three.
This, calculated back for degrees, would be 14.4 degrees either way, or about 29 degrees total TDC rotational 'free-play'.


Five gallons would be about 16 hours on the engine.
You did not indicate what fuel you are using. This is an ABC, tapered-bore engine and it needs some Castor oil in the fuel; I would say 8% of the fuel as the minimum.

Klotz BeNOL forms less soot than Baker's AA.