Thanks for a lot of good information and possible solutions.
As I stated, initially the engine would try to start, sputtering as long as the starter was cranking. Sometimes popping back through the intakes. Twice I got it to run when the starter was released but wouldn't increase in RPM.

When I discovered that the distributor advance bolt was only hand tight, I tried playing with that and considered the possibility that it might have been removed and reinstalled incorrectly.
As I played with the timing adjustment, I found I was no longer getting any attempt to start. I checked and I was getting a weak spark when I pulled a plug wire and connected a spare plug/grounded. Reset the distributor to #1 TDC (verified) top of compression stroke by observing valves). Varied timing within range, etc.. Still no start attempt at all. Not even a back fire.
This engine has a solid state distributor. with the coil inside the distributor (under the dist. cap), reluctor and ignition module under the cap as well. Cap is in good condition and appears as new, wires are fine also and in proper order. Plugs are as new and are resistor type (I think, they have an R in the number?)

I'm also wondering if there could be a problem now in the Mixer, as a result of the back fireing thru the intake valves, previously. The reason I raise this point, is, when I remove the LP gas line from the side of the mixer body and crank the engine over, I feel absolutely no vacuum even when I open the throttle. Is there something that could have been damaged or ruptured due the popping back thru the intake part of the system??

Steve

OK- as far as the ignition- spark should be bright blue & jump at least 1/4" gap at the spark plug end.

You are correct that the LPG system consists of a lock-off valve, regulator & mixer.

The lock-off valve (either electric or vacuum activated) is self explanatory. If electric- make sure it flows fuel when given 12 Volts. These can gum up & stick in the off position- flowing no fuel. If vacuum- make sure flows fuel when given a vacuum source. This style goes bad when the o-ring which seals the activation pin goes bad, feeding LPG through the vacuum feed line, making the air/fuel ratio overly rich,no matter how you adjust the fuel mixture.

The regulator- takes liquid fuel at a maximum of 312 lbs, lowers the pressure to around 6 lbs, allows the LPG to "boil" (which converts the fuel from a liquid to a gas), and also acts as a secondary fuel shut-off- allowing fuel to flow only when a vacuum is sensed through the fuel delivery line. These can gum up, not allowing fuel to flow when the unit is cold. The symptom of this is the engine will start (usually a hard start), & the engine will only idle. If you give the gas pedal any movement, the engine will starve for fuel & stall. If the engine is allowed to run long enough, this symptom will go away & the engine will run normally. As L1ftmech stated, they can also fail to regulate the fuel, sending much higher fuel pressure to the mixer than the mixer can handle. Symptoms of this are icing of regulator, usually will only run at higher RPMS (will flood & stall at idle), & extreme burnt smell of LPG in the exhaust.

The mixer- takes in vapor fuel, mixes this fuel with incoming air, & feeds this mixture to the engine. It also acts as the third fuel shut-off- allowing fuel to flow only when a vacuum is sensed through the throat of the mixer. These fail because the main diaphragm becomes stuck to the fuel outlet in the throat of the mixer. Engine backfires can also rupture the body of the diaphragm.

As you can see- engine vacuum is the key to this system working- no fuel will flow without it.

Symptoms of this type of fuel system are usually pretty straight forward. If you find an issue with any part of the system I would recommend that the entire system be re-done. As EdT stated, a engine tune up would be a good idea too.

Hi
Have you checked for an air lock in the cooling system at the vaporiser?
This can cause freezing.....

Hmm!
I assume you are talking about the larger fuel supply hose (about 1/2") going from the vaporizer over to the side of the mixer?

I took that off at the connection elbow, at the mixer and I couldn't feel any vacuum "draw" at all while cranking the engine over. However, the throttle might have been at idle during this test. I'll go back and check this again.

On the distributor, I have verified that there is spark, although weak, while cranking. I determined number one cap terminal from a marking on the cap. Removed number one plug and rolled engine over with wrench til timing mark is at TDC and verified, with a screw driver thru spark plug hole, that #1 piston is at top of stroke. (I was going to take valve cover off to confirm this is the top of the compression, not the exhaust stroke, but the rigid water lines have to be removed to get that off. )
This distributor is solid state with the coil built in and under the cap. Parts house can only get a complete distributor, replacement reluctor and modules not being shown. Vacuum advance works ok. Cap and wire are in good condition. To verify spark, I put a plug into the #1 wire and grounded it while cranking. Weak spark but still there.

I'm going to go back and take compression readings again today to see if I'm still getting the 190# that I got before I purchased this fork lift.

Steve

this is normal Steve, it requires vac on that hose to allow fuel to flow. no vac and no fuel is correct and what you wanted to see.
I would offer that the correct path would be to start at the beginning and confirm that #1 spark plug is firing when the crankshaft is just before tdc by looking in the distributor with the cap off and confirm the rotor location in relation to the mark on the crankshaft pulley. and then confirm or do a complete tune-up

Looks like the problem is in the vaporizer since I have tested the vacuum lock out assembly and it releases liquid over through the inter connecting line each time I crank the engine over.
However, when I remove the gas line from the vaporizer outlet, to the mixer (carb) throttle assembly, I get absolutly nothing now.
Originally, I was getting some flow because I it did fire and run a little. Now, I get nothing.

Might be time to order a rebuild kit.

I did find some operating description online with parts break down. Just in case the kit doesn't provide any.

Thanks

Steve

Hi first you shouldn't be getting any frosting on components at all this usually points to either a leak of if its the vaporiser a cooling fault. First thing to check is that coolant is getting too and passing through the vaporiser if it isn't the vaporiser will frost over then freeze up if this is happening this will give the problem you have ive had water pump impellors fail that give this fault. I don't know if you can buy kits over there for the J type impco but if you do stip it there is a strip valve with a rubber seal in the middle these are prone to failure and you wont get it to start if it is they fail due to the body wearing where poppet that works on the hp diaphragm wears. My advice if you cant get a repair kit would be to fit an imcpo k type to it.

Steve with known fuel in the lines, take the large LPG hose going from regulator/vaporizer to mixer off the mixer. With fuel shut off or disconnected from tank, spin engine over. If fuel comes out then you have a vaporizer that needs replaced. The frost you are concerned of is evap of LPG. Check coolant level also. If unit has vaccum lockoff then check for LPG coming out of vacuum line on lockoff.

Thanks for that tip. I did try that and since the tank valve seems to have a leak thru, even when turned off, I think I still have pressure until I disconnect the tank coupling. Something I will deal with when I refill the next time.

Now, onto the LP gas fuel system.
From the quick research on Google, it seems the be made up with a converter, mixer and the carburetor.
If my problem is flooding, then where should I start? Hmmm!
I would assume the liquid fuel would be converted to gas through evaporation in the converter and that process would account for the frost I observed on that case, since the coolant temp wasn't yet high enough to assist in that process.
Not sure what the Mixer does??

As I search ebay, I see there are parts kits for the carboretor but nothing for the mixer or converter. I don't see any adjustments on either of the latter. The carburetor only has an Idle adjustment. Three is some kind of adjustment in the lower carburetor mount plate that looks like it not be "field serviceable" (seal wired).

I'm going to go back to google and search for other trouble shooting help.

Still hoping someone here will have some "Sage" advice?

Thanks
Steve

Your statement about "frost on the propane stuff" makes me think that the J-model fuel regulator (what the coolant hoses run to) is leaking liquid propane into the intake. What you think is acting like it's out of fuel is in reality probably "over-fueling". I have always found that a simple way to test this is to shut off the supply valve on the propane cylinder and see if the engine begins to run better as the fuel in the hose is consumed.
If the condition is due to over fueling, the engine may seem to run "about right" just before it uses up all the fuel in the hose and dies.

I just checked and verified that the plug wires are correct.

Now, I have to verify that the last person to have the distributor out, put it in correctly.

Steve

And yes the firing order is 1-3-4-2

Have an email to post in your profile has to be as mine is as this site strips out readable addresses

I just checked the distributor and the mount/adjusting bolt was loose.
Now I have reservation and think this problem is timing or in the ignition system. I tried varying the distributor within the adjustment range, but not positive results. Then I began to wonder about the plug wires and realized I don't know the firing order of this 4Y engine. Toyota 4 cylinders have had of 1342 or older Corona's were 1243.
I checked for the firing order on the engine but didn't see it on the manifold.

Since the distributor mount bolt was loose, I suspect the whole unit might have been removed and re-installed. Hmmm, could be of a tooth when re-installed. Another possibility.

Without a manual, I'm going to have to play around with this one.

Steve