Gentlemen, I have a 1980 former school bus with the 404 International gas engine in it that was converted to propane years ago. Bus has been sitting for over 10 years. I'm trying to start it but I have very little knowledge of propane conversions. I put a new battery in it and it cranks over well and it has spark at the plugs but won't fire.

I tried bleeding propane out of the tank under the bus and it seems like the tank is almost empty, no white gas vapor came out, just a weak air stream. I hooked up a full 5 gallon propane tank straight to the bus feed line to what would be the carburetor and it still won't fire up. I shot some ether (starting fluid) into the unit that replaces the carb and the engine will start and run for a few seconds until it consumes all the ether.

Where do I go from here? There is a regulator under the hood, maybe something wrong there? I really don't know what else to to try. I'm handy with tools and do all my own vehicle maintenance, I just don't have any experience with propane conversions.

Thanks for any and all suggestions guys!

JK

The gas line solenoid the first check, 12 volt & when the key is turned on it should energize & allow fuel to flow to regulator. In & out of the reg. the next step.

This, and I would plan on ordering a rebuild kit for the converter/vaporizer. When we ran our trucks on propane at my job, we would rebuild them every year. If iirc, they were a impco product. They can get quite dirty and impede the flow of fuel.

Good luck!

Our hysters were not conversions.

But they had the same parts. We had more problems with the vaporizor than anything else. Clean fuel, as per our mechanics, is of paramount importance. The service techs could identify problems caused by crappy fuel from cheap suppliers.

I have almost no knowledge, but I am thinking maybe the regulator has fowled from sitting dry.

My mom had a gas log fireplace and ran out of LP... there was a bleed-out process IIRC.

Something about purging a system that sat without "wet" LP lines and air/moisture maybe???

Same thing with our gas fireplace last year. We let the propane tank get empty over the summer. The tank is 100 feet away from the house.
We had to crank the delivery rate at the fireplace way up to more quickly purge the line before it would fire.

My son is a Journeyman HVAC technician. I let him play with the gas lines and valves.

In an automotive situation, one might have to break the gas line in front of the vaporizer and make sure gas is flowing. It should be easily detectable by odor.

This.

Used to work an un manned platform that had a little natural gas generator.
We would start it to charge the NavAid batteries. We had to pull a plug out of the intake and purge the fuel line before trying to start it. when we knew we had gas to the engine we would screw the plug in and fire it up.

Propane tanks are usually certified for 10 years or there abouts. If your vehicle has been sitting for some 10 years with an empty tank, probably means it is somewhere between 10 and 45 years old and full of water, rust, and all kinds of grit, and not likely safe. Same with all lines, regulator, and the carburetor. Won't none of it be usable, though you might be able to put a rebuild kit in the regulator and carb. I damn sure wouldn't take a chance on the tank.

Phil

Don't use ether. Use propane to start it. Any time you have the urge to use starting fluid on a spark plug having engine.....use a propane torch (unlit obviously). It's perfectly atomized and won't cause any potential damage like ether can.

Forklift tech here...you say the battery cranks the engine over, find a vacuum port and put a gauge on it.

You say , it runs on starting spray so you probably have some vacuum...is it enough??? you need to see the needle move on the vacuum gauge.

Now follow the fuel system and open slightly each connection from the tank headed to the intake, one at a time, each end of the hose, into and out of the "lockoff valve" then to the "converter"(usually round aluminum housings, with fuel in and out and coolant in and out of the converter),as you progress tighten the previous and loosen the next connection from tank to mixer....

most often there is also a vacuum port...the slight negative pressure(engine vacuum) unloads the diaphragm on the lockoff and allows fuel to flow. The odorant that is in LPG will stick the diaphragm, or no vacuum, or not enough vacuum=no fuel flow...

you don't mention LPG smell when cranking, but the opposite problem can also cause no start...LPG free flowing into the mixer(think carburetor)= "flooded" engine, but you will smell...may even be able to see the swirls of fuel out the throat of the mixer...

also one additional thought comes to mind...typically LPG vehicles use liquid propane as fuel, that is converted to gaseous state, just before the intake...small LPG barbecue bottles take gaseous LPG from the top of the tank(no dip tube)...LPG vehicles use liquid propane by pulling liquid from the bottom of the tank through a dip tube.

Hope this helps.

You said it has been sitting for 10 years and now it cranks over well with a new battery. Have you done a compression test? Sitting that long could easily have some stuck piston rings and low to no compression.