LPG System

Not a tractor, but close...

A Mitsubishi FGC 25 lift truck with an Impco factory LP system.

It has run flawlessly for many years with no PM on the fuel system at all.

Here lately it has begun to intermittently run really rich, burned propane stink, black around the exhaust, excess fuel consumption. There is no really noticeable loss of performance or starting problem. It might do this once a week, then run normally, seems to be worse in colder weather, but it lives inside the heated shop, so no real temperature differences.

It has always had a raw propane smell immediately after shutting the engine off. I attribute that to the engine coasting down with the spark stopped. There is no fuel cut off solenoid.

There are 3 main components, a high pressure regulator, a vaporizer, and the throttle/governor assembly.

I see a lot of Youtube videos on rebuilding the vaporizer. Looks simple enough.

Is that the most common area of trouble?

I have no idea where to start an official "by the book" diagnosis.

Any ideas?

Thanks!

Probably vaporizer trouble, they are not hard to repair. The diaphragm and/or fuel vapor valve on the low pressure side probably needs replaced. Impco LP equipment has been the least trouble on any LP engines I have had. Find out which model you have before looking for parts, used to be E and J were most common. Been awhile since I've worked on any LP engines though.

I ran an Impco Propane system on my Lincoln Continent...460 Engine....1980 Ford F350 400 Engine...1973 Olds delta 88 ....

It has been some time now ..possibly the Impco was a Model 420? 425? 450?

Vaporizer was only component that required parts replaced (diaphragms. Surprising how much BLACK GUEY CRAP) ...once per year also an inline fuel filter...looked Like a roll of COTTON CORD / STRING)

Bob..

You will find that some suppliers of propane have more black goo in their propane then others. It can even vary load to load. I would open it up, clean it all out. Check the filter and there should be a vacuum tube to start/ stop fuel flow based on engine vacuum.

Was probably the Impco 425 mixer with the model E vaporizer. I had the same setup on a turbo Olds 455 in a C10 Chevy years ago. Boy, that truck was FUN!!

Steve, look for a turnbuckle linkage on the carburetor. If it is there, a knurled tube with a locknut on each end is the fuel mixture adjustment. After you have removed and cleaned the vaporizer like others have said, and replaced the diaphragm and get it running, you can adjust the fuel mixture with the turnbuckle. Set for smoothest idle. This raw propane smell tells me the there is a hole in the diaphragm. It will be so tiny as to be hard to see. take the diaphragm in your hands and stretch it really tight over a light. If you see light, you have a hole. When everything is all put back together, remove the flexible hose that goes from the vaporizer to the carburetor. With gas valve on and key on, there should be NO GAS come through this hose. The vaporizer regulator is set to atmospheric pressure. It takes the vacuum from the engine cranking over to move the gas through the carburetor and in to the engine. If you have gas coming through the flexible hose with it disconnected fro the carburetor, DO NOT run the machine in this condition. You will have a crankcase explosion if you do. All this is experienced first hand by ME. I was trained by an LP Gas dealer. I kept trucks and farm machinery running as well as fork lifts at Holley Carburetor Plant. Email me if you have any questions. Steve in Bruce Ms.

Impco does not use a turnbuckle, Century did..

Thanks everyone.

I did some more research...

What I thought was a high pressure regulator turned out to be the "pressure lock off" valve, the valve that opens only when there is engine vacuum present.

Though I don't think there is a problem with it, that's where the fuel filter is, inside the valve. So I ordered the repair kit.

And ordered the kit for the vaporizer.

I found repair and test instructions for the vaporizer on the Impco site. No special equipment needed.

It may be after the 1st before I get the parts and get into it. I'll follow up how it goes.

Thanks again!

10+ years ago, I was the mechanic for a factory that had about 30 forklifts, about 3/4 of them were propane. Those vaporizers can be problematic, but fairly easy to rebuild. As noted, sometimes the propane that they used was dirty. I was always amazed how much dirt would be inside a lot of those propane lines.