We've got a Yale at work, 4 cylinder propane powered. Symptoms are low power and has to be cranked for about 40 seconds to start the first time of the day. Will fire instantly with ether or when it's been run recently. I checked the throttle linkage, the throttle opens all the way when the pedal is floored.

 

Check the propane regulator. seems propane is not as clean as it used to be. My manlift had a waxy goo in the regulator.

 

I used to get similar issues on occasion with my almost new Hyster. As electrifried said, this goo accumulates in the regulator and clogs things up. On my lift I would start seeing puddles of it under the truck too. My mechanic said this often happens if you are using a steel propane tank because moisture builds up inside the tank and then it mixes with the propane. I have had one regulator replaced and one rebuilt in the last few years because of this. I finally went and got some aluminum tanks....

 

Drain the tar from the vaporizer first. The head of the plug fitting takes a 7/16" wrench. Squirt some brake cleaner in there too. Helps the seat on the end of the diaphragm move easier with vacuum. What kinda hours are on it? If it's a high hour machine, it may need a cam. Your symptoms sound like a vacuum problem to me.

 

I found some more info online about how the system works and did a little quickie diagnosis this morning. Seems the lockoff (Impco VFF30) has a vacuum leak, you can't pull a vacuum on it. The local forklift parts place didn't have the rebuild kit in stock, but they did have a new one. For $50 the boss said go for it, so we'll see how it goes when I have time to put it on. I could pull a vacuum on the new one so that makes me pretty confident I made the right call.

I'll hose out the vaporizer too while I have the system open.

I don't think it's got a lot of hours on it, I'll have to look at the hour meter though. The company bought it about 7 years ago and an hour of use in a day would be a lot when it was at the main plant. Now that it's at a branch location it might get run once a week for a couple minutes.