Originally Posted by DaveyMo

Greeting All Again:

Well, here's the scoop. I tried three different props over the last couple of days (9x6, 8x6 and 7x4). The engine starts predictably well with each of them (though a good ten flicks to get some fire in the jug on each). It seems to run a bit smoother with the 7x4, so I will stick with that. The 7x4 is a black Master Airscrew, very sharp. I cut my finger just installing it on the prop shaft, so a leather glove is my starting friend!

Now, I need some more help. Between the three different props, I've put perhaps ten minutes on the engine in half a dozen slow speed runs. Am using Davis Diesel with just a little extra castor oil added. It will run through the mustard jar of fuel without a problem, but I can get it to run no faster than perhaps 6,000 or 7,000 RPM (I've got no tac). I'd like a bit more out of it before I go through the heat cycling.


Here're the particulars. I can start it at a compression setting of 12.5 turns in and a needle setting of one and a quarter turns out. As I understand it, my goal is to back off on compression after a minute and then find the needle setting that gives highest speed. I then repeat this process (backing off and then diddling the needle for highest speed at each lower compression setting). However after backing off the compression in three or four steps or a total of a half turn out from its starting setting, the speed has crept up very little and seems to max out at the 7,000 or so RPM. In trying to reduce the compression even more, the contra piston fails to cooperate and stays in the 12 turns out position while the T-bar free-wheels on top. As it runs, I'm getting nice, white smoke and just a bit of gray discoloration in the fuel accumulation below the exhaust port.

Any advice? I haven't tried increasing compression from the starting setting to see what that does to the RPM. That sound backwards, but is that an option?

This engine is a bit of a challenge, but it sure is a beauty!

Dave...