Propane forklift runs rough at idle

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!
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Gunner, I want to make sure we are on the same page, is the mixer the carburetor, or the vaporizer where the coolant goes?
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wrote:

Good post, mon. Saved for later reference.

The way it looked to me, the regulator takes liquid fuel and converts it to gas, then is adjusted by the vacuum from the intake (like the butterfly in a carb adjusts volume), and the mixer simply moves the propane into the intake airstream (as a carb does with liquid gasoline) for burning. Do I have that right?
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OK, guys, thanks. I am getting rebuild kits for both the Impco Series K vaporizer, as well as the Impco CA55 carburetor.
i
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Right

Gunner, thanks. I will rebuild both the vaporizer, as well as the carb.
This is actually an older, but very good forklift, it has a very high lift.
i
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It has a separate fuel shutoff based on engine vacuum, another pancake that is before the vaporizer.
i
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On Sun, 07 Dec 2014 20:15:40 -0600, Ignoramus7467

My first guess is a vacuum leak (or poor ignition). Failing that, possibly a problem with the demand regulator
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wrote:

+1 on the diaphragm - if it isn't a vacuum leak in the intake the diaphragm on the demand regulator is the most likely problem. When I had my Propane service licence we were taught the diaphragm on a vehicle propane regulator MUST be replaced every 5 years. That was 30 years or more ago, but the design of the things hasn't changed.
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On Sun, 07 Dec 2014 20:15:40 -0600, Ignoramus7467

*
First and foremost, look for vacuum leaks*. That is the usual cause of no response from the idle mixture screw.
Flynn's had a wrecker with a propane conversion, and I drove it a few times, but I never had to work on it. I wish I could tell you more, but I only looked at it. It got lousy mileage, so I never considered any conversions of my own vehicles.
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OK, great, that vacuum leak, where would it occur? In the hose or in the diaphragm of the carburetor? Thanks
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On Mon, 08 Dec 2014 10:04:37 -0600, Ignoramus28939

Anywhere on the engine can cause problems. But the one to the vaporizer is key.
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To: ignoramus7467@NOSPAM.7467.invalid On Sun, 07 Dec 2014 20:15:40 -0600, Ignoramus7467

*
First and foremost, look for vacuum leaks*. That is the usual cause of no response from the idle mixture screw.
Flynn's had a wrecker with a propane conversion, and I drove it a few times, but I never had to work on it. I wish I could tell you more, but I only looked at it. It got lousy mileage, so I never considered any conversions of my own vehicles.
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To: Larry Jaques

OK, great, that vacuum leak, where would it occur? In the hose or in the diaphragm of the carburetor? Thanks
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wrote:

Good post, mon. Saved for later reference.

The way it looked to me, the regulator takes liquid fuel and converts it to gas, then is adjusted by the vacuum from the intake (like the butterfly in a carb adjusts volume), and the mixer simply moves the propane into the intake airstream (as a carb does with liquid gasoline) for burning. Do I have that right?
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To: snipped-for-privacy@invalid.diversifycomm.com On Mon, 08 Dec 2014 08:01:49 -0800, Larry Jaques

Pretty much. Some actually have a "choke" which feeds slightly richer fuel/air...most do not but some have a "primer" which will give a shot of propane on key-on or first crank
My Linde/Baker with the VW engine does just that.
Gunner
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OK, guys, thanks. I am getting rebuild kits for both the Impco Series K vaporizer, as well as the Impco CA55 carburetor.
i
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To: Gunner Asch

Right

Gunner, thanks. I will rebuild both the vaporizer, as well as the carb.
This is actually an older, but very good forklift, it has a very high lift.
i
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To: ignoramus28939@NOSPAM.28939.invalid On Mon, 08 Dec 2014 10:15:29 -0600, Ignoramus28939

Some/many forklifts have either an electrical or mechanical fuel shutoff..ie a solenoid..so make sure that its working properly as well. When you turn the key on..it should Click! and pass fuel through it. When you turn the key off..it closes off the fuel to the carb OR vaporizer. Mine has a solenoid because my vacum operated one quite working and after I rebuilt the unit..I left it in line. I dont have to turn off the fuel at the tank when I walk away from it (though I do)
Gunner
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To: Gunner Asch

It has a separate fuel shutoff based on engine vacuum, another pancake that is before the vaporizer.
i
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