Just bought a 79 bronco on propane that wasn't running. It is an impco system, and after fooling around with it i was finally able to get it started by holding the relief spring on the vaporizer but as soon as i let go it dies. Any help with this problem would be appreciated, i have the local mud bogs coming up.

 

Vaporiser needs to be rebuilt. Secondary diaphram (big one) probably has a tear in it.
That happens sometimes with a severe backfire. Also if it has hose between the vaporiser and the mixer(carb) check it for holes sludge etc

 

Hi I also have a 79 Bronco on propain ..and learning.. mine is a 428 Fe ..so I gotta ask how is your bronco doing ??and where would sludge come from on a propane system ?? can a backyard mechanic (us) rebuild a mixer safely ??where do you get parts from .. Oh yah Hi ..I'm ken....

 

The "Sludge" is called heavy ends, The vaporiser acts like a mini refinery and breaks/refines it out. It is mostly the strnch that is added to the gas at the terminal.
Generally if you will cool the vaporiser you will not get as much. You only need 120-140 degrees for the vaporiser to do its job. Yes most anyone can rebuild the vaporiser or mixer if you get a kit and FOLLOW THE INSTRUCTIONS that come with it. Your Local Propane supplier Should be able to order you the nessisary repair kits to do your repairs.
Regards

 

If you can rebuild a gas carb you can rebuild a regulator. The main thing is to be careful with diaphragms and gaskets to prevent leaks. If you find a lot of greasy residue inside it can be oils that settle out of the propane as it vaporizes or it can be valve grease from the cracking plant put there by an over-zealous workman. The suggestion to keep the coolant temp low in the vaporizer is a good one. If you can, orient the regulator with the vapor outlet down so that the residue tends to go through the engine. It's just more hydrocarbons and the amount is generally slight if it isn't allowed to build up. One symptom that turns up in dual fuel apps is that the engine won't start on propane, only on gasoline, then can be switched over when warm. That's almost a sure sign you have gunk in the regulator. It solidifies when cool and liquifies at higher temps. Good luck.
Keith