Jim,

The valve between the gas solenoid and engine is just a Festo regulator or more correctly, an adjustable restrictor, I use it to regulate the amount of gas during the start sequence, I find it's very usefull when changing out empty gas cans, once I had the adjustment set correctly, (took me three or four starts to get it right), I can now just change gas cans and not worry about adjusting gas flows, pretty much a set and forget affair, works a treat too! Alternatively, you could fit a fixed restrictor in the gas supply line, something like 0.5mm or so, I believe some engine manufacturers do this allready. I like to turn my gas supply off when the engine isn't being used, simply because if a solenoid fails to close completely after shutdown, you'll get small amounts of gas leaking through the engine, not only is it a fire hazard, it wastes your gas too!!

I guess it comes down to the type of gas you're using and the pressures supplied by the can itself, no two set-ups would be the same I expect so each individual system would need it's own fine tuning to get it right.

Cheers,
Smithy.