I have a Kalmar C50 forklift. It has a impco ca55 carb and impco kb mixer.

It runs rough at idle.

Here's the description of the problem:

1) Kalmar C50
2) Nissan Engine
3) Impco ca55 carb and impco kb mixer/vaporizer
4) After a day of sitting, it is hard to start
5) Once it starts, it runs rough at idle and often dies when put in gear without pushing on gas first
6) Generally after I push the gas pedal, it runs strong
7) With gas pedal pushed all the way, if I engage tiltback, the engine does not die but slows down (proper response).
8) When it starts running rough at idle, it may even die by itself
9) When it starts acting up and run rough, if I press the PRIME button on the vaporizer, it straightens itself out and runs good for as long as the prime button is pressed
10) There is proper antifreeze level
11) I tried adjusting idle mixture with idle mixture adjusting screw, unfortunately result was no different
12) I took out the air filter (which was very dirty), with no change in idle performance
13) Again, with gas pedal pushed, it hesitates to speed up, but speeds up and runs very strong.
14) The vaporizer is heating properly with warm antifreeze, with no frost forming on it.

I am suspecting the vaporizer unit, however I would like to see what you guys think.

I am specifically interested in a troubleshooting procedure, as opposed to part swapping. I have a lot of forklifts and want to learn how to work with propane systems.

I have various pressure gauges that I can hook up.

Any suggestions on where to begin isolating the problem?

Thanks a lot!