Thanks for all the kind comments.
Jason
I communicated with Rocky regarding the venturi. He stated that his engine runs well with the venturi as stated in the drawings. He also stated that several folks had contacted him about this and they got their engines running well only after they had increased the venturi size. He didn’t have a measurement.
You have to realize that the engine is drawing ALL the fuel/air it runs on through the 1/16th inch venturi. To me this is insanely small. I was tempted to drill it out MUCH larger, but the outer size of the venturi wall is 3/16th inch. I started with drilling the venturi out with as 1/8th inch drill. This seems to work well, and the engine isn’t “gasping” as it was with the 1/16th inch venturi. This is what I stayed with.
I also increased the size of the fuel pump barrel to ¼ inch. This might not be necessary since I was having check valve problems concurrent with this. It’s imperative that the check valves function or the gas just runs back down into the pump and the mixer starves out. I took the return fuel line and routed it to a pan on the table and verified that I got a steady stream of fuel running out the return line when I turned the engine over.
My fuel pump was seeping fuel out the top of the pump alongside the plunger and the fuel was collecting on the base on which the engine is mounted. I didn’t like this so I used a 3/8th inch drill to cut a lip into the top of the pump. I placed an o-ring on the plunger and let the spring sit on top of the o-ring; seating it in the lip I’d cut. This seems to have stopped the gas leaking out of the pump.
Finally, I advanced the spark to about 15 degrees before TDC. To do this I had to move the cam gear forward one tooth and now the exhaust valve timing for open/close isn’t exactly where I’d like it to be, but with the spark at TDC the engine couldn’t develop enough power to kick in the lock-out and I couldn’t advance the spark any more with the igniter trip mechanism as I made it. At 15 degrees TDC it hits hard enough to spin up to speed when it hits and will get the centrifugal pump to pump.
One other thing I did was to put a check valve in the water line at the exit to the pump. This keeps the water from flowing back into the pump when the RPM’s spin down.
If I remember to pump the fuel pump a few strokes so that there is fuel in the mixer, the engine starts without too much fooling with it.
Hope this helps you get your running.