LPG Vaporizer Question

I've got an odd problem on my tractor and I think it's fuel related. This is an 850 ford 172 4 cyl. LPG with an Impco Model J, which I rebuilt a few years ago, using their kit. Ignition/spark seems to be fine, plugs wires, but she is skipping. I think the vaporizer has been frosting up, it had condensate on it after I ran it yesterday. Skipping seems to go away with more throttle, it does not idle, so it seems fuel related. Coolant level is full, water pump circulating through it.

Only thing I have changed on the vaporizer was the vacuum switch, vaporizer has a small diameter line to the carb, and power from the coil, seems that it opens a circuit to the fuel shut off solenoid, when it receives vacuum, the nipple broke off the switch recently, (was running poor then) so I bypassed it, with power directly to the fuel shut off solenoid from the coil.

I'm thinking it's either the vaporizer or the carb, which I would think would be clean, though I've never had it apart. Since I rebuilt the vaporizer it had run great, just wondering what you LPG guru's think, before I take one or the other off for a look, have a little disc'ng to do, and some seed to sow, tractors sometimes have a way of doing this to ya, now don't they ! LOL

That small line MAY have supplied you idle mixture. If it did supply you idle mixture I can see why it would miss near idle and run better with more throttle. If the vaporizer was frosting from little or no engine coolant flow, which WARMS the vaporizer, you will see frost on the outside of the vaporizer. Depending on where the vaporizer is mounted it may be air locked. If the Model J is mounted with the water inlet and outlet are on the bottom it may be air locked.

Kent

Almost impossible for the evaporator to cause a miss. That model J will feed a 454 big block just fine.

No idle? I'd sure be looking for a vacumn leak.

Then, check compression/valve guide slop.

Allan

I'm not sure about that switch, newer model J's don't have em, at least ones I've seen on e-bay and other suppliers. Previously, if that vacuum hose came off, it would not run at all. Seems all the vacuum switch does is operate the fuel shut off solenoid, this vacuum switch was mounted on the impco model J, on the bottom, but completely separate from the vaporizer, which appears to be an older model J. With the bypass and the vacuum nipple left open, it did not seem to run as well as with it capped off, that's how it is now.

Coolant lines come in from the side, now I wonder, not that long ago she was overheating, think that may have something to do with it ??? Maybe the boiling over and hot steam is what did the air lock or maybe screwed up those diaphragms inside?, I put a thermostat in, took care of some other related things and back to running normal temperatures, looks like I'll pull that vaporizer off and see what's up in there, she won't start not anyway.

Seems to be a good running motor with 50lbs of oil pressure, no blow by etc., well once I see what's going on inside the vaporizer and check the carb for gunk or obstructions, valve cover is easy enough to get off, leaking a bit anyway, and a cinch to check compression with the spark plugs easy to get to. Something new to me, as I'm puzzled, but think that overheating recently and the vaporizer may be the place to start. I released the fuel pressure in the fuel line to the vaporizer, but when turning it over, no odor of LPG out the exhaust if my nose is correct LOL !

It will idle, just need to move the throttle lever up further to do it, before you could set it right down to nothing and it would still run. I had a no start situation late spring early summer and determined it was a fuel problem, once I gave that carb a little snort, it fired, thought it was the float in the 30 lb fork lift type tank I was using, LPG supplier had mentioned that, switched tanks this time and it did the same with the suspect tank replaced.

Well heck, it's one of the few times this tractor has ever acted up, suppose it's due for a hissy fit LOL !

the small line is a vacuum line to your fuel lock off & needs to be on there ..the model J is Impco's smallest converter & is good for about 100HP ...the Model E & L are rated at 325HP...Google Impco & read...I use the Model E's when I replace the Century reg.'s on my John Deere 2cyl's...take care ...Kent

You might be right, it would seem that the solenoid will cut off fuel as soon as the key is turned off, with the switch on, key can be on, but if the engine is off, no vacuum, switch is open, no power to the solenoid, = no fuel, which of the 2 scenarios I would think to be a tad safer, if say that impco or fuel system were to leak. Funny thing is I do not see that switch on any of the new Model J's or similar, nipple broke off mine.

Incidentally, I disassembled the vaporizer, only rebuilt 3 years ago, looked fine, + a new fuel shut off solenoid then too, still no start, well, it has been probably 5 years, with moderate use, breaker point gap was off, reset at .025, and it runs crisp, I had some sort of a fuel problem before, led me to believe that was it, but keep workin at er, something simple.

Allan, you were absolutely right on that, I disassembled that vaporizer, nothing wrong at all, kept at 'er no spark, and turns out to be the breaker points, yep electronic ignition would be better, but I think it's been exactly 5 years since I put a set in or adjusted the gap last, runnin crisp again, like she always did.