I'm having some trouble getting an old clark c20b running.

It was running ok but had some problems which need fixing. I replaced the head gasket, the muffler, fixed a break seal.

After putting everything back together it wouldn't start and backfired. I checked distributor had it 180deg out of time. I fixed that and got it to what I thought was good timing. It would turn over, but never start.

It is a LP system and you could smell some gas after trying to start it for a while. I pulled the front of the regulator/vaporizer off and when you pressed the by-pass button you to hear the gas come out.

I replaced the battery, coil, points, wires and plugs. It now will backfire consistently if hold the by-pass button down, but not start.

The lockout value on the vaporizer seems to be working (I can hear it click when key is turned).

Any suggestions on trouble-shooting?

Thanks,
Scott