Ok this is do-able with a carb. There is a kit available at www.gotpropane.com that will likely work for you. Ian from Extreme 4x4 used this for one of his projects.
The only thing that I was a little iffy on was the implementation of them. You get a 3 position switch, left is gas, right is propane, and middle is neither. With the switch on gas you have to turn to neither, let the engine begin to stumble, then go to propane. I hate letting my engine start to stumble.
300 CI bored .030 over with a 240 head (303 CI). Clifford valves, Comp Roller Rockers, crane cam, Offy intake, true dual headers, x-pipe, pretty spicy.
The GotPropane systems are geared towards off-road systems and use DOT (lift-truck) tanks. For on-road vehicles, these tanks are generally not permissible and ASME tanks would be a better choice. You should familiarize yourself with the regulations in NFPA 58: Liquefied Petroleum Gas Code.
Your truck is early enough that it probably doesn't need any add-on propane system controllers. Later vehicles would have required sort some of integrated processor from Dual Curve but these products are now obsolete. Having two advance curves for your truck would be ideal and the only commercially available dual-curve system I'm aware of now is based on MegaJolt Lite. AutoSport Labs makes this type of ignition system.
Thank you very much for your very kind ... and VERY informative reply.
Although I was an auto mechanic for 30 years ... mostly on foreign cars, I was the working shop foreman and, later, the service manager of a Porsche Repair shop and Bosche Warranty Center, I am frankly a nube with regard to this technology.
Having said that ... it honestly doesn't look all that hard.
As I mentioned my truck is a 1982 F100 ... 302 V8, 4X4, Stick ... it has a stock 2 bbl carb and a standard Dura Spark II ignition system.
I live in North Georgia ... my county has NO vehicle inspection ... and I will be registering the truck for hobby use. It will only see rare hi-way use.
I will be building a step-side box for the back of my Ford ... and mounting the spare(s) on its sides. That leaves all of the space underneath for mounting fuel tanks.
The reason I am looking into these (and other) conversions ... having multi-fuel capability ... gives you more options in times of high prices and scarcity of supply.
Relays and solenoids are simple and reliable ... wiring them in will be a piece of cake.
However, for reasons of simplicity ... and "Craftsman Hammer" reliability ... I would not like to get involved with these types of ignition systems. As a matter of fact ... my plan is for "back dating", crazy as it seems, to a 1974 or 75 distributor ... with points and condenser. Dead simple ... utterly reliable.
I found Gotpropane sometime ago ... interesting ... to be sure.
I've bookmarked the sites you suggested ... I've read some of the information ...
I would think that the main reason you want a propane system on your truck is to have lower operating costs. My guess is that there will always be readily available gasoline in the USA but the cost, as you suggested, could again be very high. If you install a propane system (or any alternative fuel system) on your vehicle, you should really plan on using it as much as possible to have the fuel savings pay back the cost of conversion.
Propane (and CNG) places high demands on an ignition system and most conversions at least use an electronic ignition system with top quality components. The ignition requirements for propane and gasoline are different so you can only optimize one fuel's fuel economy and power with a single curve distributor. Dual Curve used to make an add-on advance controller but many people weren't impressed with its performance. Generally, propane can use more initial advance but requires less total advance. If you just stick with the OEM advance curve, you could potentially have too much advance for propane at some operating points. A commonly-used, generic advance curve for propane systems is 14°+14°+14° (initial + mechanical + vacuum).
As for conversions, I haven't personally done any dual fuel conversions that I've provided links for. Conversions aren't hard to do but some are more complicated than others. As with anything, doing a good conversion comes with experience and care. However, it is also important to follow the regulations as they are there to protect you and others around you. I would also suggest that you get a local conversion shop's advice before you start and have them inspect your work BEFORE you put any fuel in it.
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