We had a different technician take a look at it with a new set of eyes. I embarrassed to say that the problem was bad spark plug wires.

Any chance you're still out there and ever got that thing fixed? I

Hey which type of lp regulator is it. i have had a similar problem before and even though the regulator had been done before that was the problem Rich

No. The customer ended up trading in the truck and now it is my problem. We did find that once the engine was running, that in order to keep it running, the distributor would need to be turned significantly- which changes the timing. Once the engine was shut off it would not start again unless the timing was changed again.
We pulled the engine, front cover, timing gears and chain. The thought was that a keyway was worn on either the camshaft or the crankshaft causing the timing to continually change. They ended up being like new. We pulled the distribotor and checked the gear which was good as well.
So it is on the back burner for now but I would sure like to get it fixed without pouring much more money into it. It would be nice to know that we have cured the problem before we reinstall the engine.

your keeping very quiet duodeluxe have you found the problem and keeping it a secret

for my wag (wild as* guess), I would go with a wiring problem to the coil, (like combar said) or the coil itself, and if that is not it, then (like simon_k said) the suction hose from the carb to the regulator.
change the hose that the fuel travels to the carb in, change the diaphragm in the carb (unless, as you say, you know the carb is good by installing it on a known good unit,) and run a jumper straight to the coil from battery positive. this may well even just be the contact for the "run" position inside the key switch, or the wire on the back of the key switch, either run or battery positive being just a little loose....

Hi! duodeluxe:

This will be a guess only or good suggestion to you:

Have you tried to start the engine stand alone?

what I meant is: disconnecting all loads attached to it (transmission and hydraulic pump)? Chances are the Hyd pump gets jammed by something in inlet port I (a rag, paper, plastics etc) applying a really heavy load to the engine when starting -up also bad converter/transmission can cause this malfunction.

Try this shut gas off drain lines of LPG and remove the air hose going into the carb after that get a small rag gas soaked and put over intake and crank see if it will run of gas. If its flooding it will cause this wear it will try and try and try to start and then backfires it sounds like the reg is bad. Those reg Su2k 2 get right. U may want to remove the air mix screw and tighten all the way in and then back 3 full turns I found that's a good starting point. After that get a heater hose tee splice that in and hook back up and with the 3rd fit ur vacuum gauge in and crank see with the carb is seeing for fuel it should not go over 3.5 psi and with the 1/8 pipe tread it should not go over 1 psi and before u try cranking I would check the firing order that's to ez to over see and that will send u for a spin also check fuel flt also don't want a dirty flt

i just remembered that i had a problem with a clark that had a mitsu engine when i first started working on forklifts

it wouldnt start but when it did it seemed to run fine
after beating my brains in lol another older tech told me to try changing the pressure relief valve for the LPG up on the rad cover
sometimes they go bad and wont let the engine start but if you manage to get it running it will run fine

that was the case with that truck
its a cheap and easy thing to try and it looks like youve tried everything else

(how funny would it be if you just had a square cut o-ring from the tank stuck in the LPG connector lol)

i believe the backfire was part of the issue too but it was like 9 years ago so i dont remember the exact symptoms

I'd tend to go the way prentice said. Change the vac pipe between the inlet manifold/carb and the gas regulator. If the regulator doesn't get decent suction it will not let anything through.

not sure if ignition coil has a ballast resistor if it has check or replace it also try running a heavy cable from batt positive to ign coil and see if it starts any easier one other thing if the inlet and exhaust manifold are joined check that there are no burn through to inlet side

try changing the fuel delivery lines (maybe cracked and collapsed internally)
check for a plugged exhaust or intake
check the starter , maybe the pinion clutch is weak and not spinning the engine fast enough?

sounds like you checked everything else

did you try changing the governor and the throttle plate?
maybe one of those is pulling extra air in
warpage at the intake manifold to head? (but your vac reading would be low then)

Check the simple stuff first- SPARK- FUEL-COMPRESSION- If you have all three - it will start.

Check for a torn/popped carburetor diaphragm, Propane coupler faulty ( Quad ring stuck in there). *** on the vacuum lock off line and see if any fuel comes out of the carburetor

Make sure your firing order is correct ( Spark plug closest to fan is #1) Check timing marks

You have compression it should attempt to start or run rough

Hope this helps

It. is a 125, but we have taken a 100 and a CA55 of other trucks and had this engine running on those mixers.
It is almost like there isn't enough vacuum to *** the gas into the mixer but if you put your hand over the air horn it seems to have plenty of suction and it doesn't really help the engine start any better when we do that..

What kind of Carburetor do you have ?????? M#100-125 ????