The point about using '70's & '80's engines works well for simplicity, ease of
service, and Locost: the major concern is that of emissions standards. I have
not checked for prior mention of propane fuel in this group, but I can recommend
it beyond the emissions issue for the sake of engine life, reliability, a
customary 10% discount in price, and general availability- every town has a
propane outlet somewhere. I speak from the experience as the owner of a 1964
Ford Econoline van that I converted to propane use, back in 1981 (when gasoline
seemed about to double in price to $2)
The procedure is straightforward, as plumbing standards go, with main concerns
providing space for the regulator and fittings for the carburetor (in a
dual-fuel configuration), and designing around the clunky fuel tank, tho the
hurdle of getting a homebrew installation approved is formidable. The cost of
getting it installed commercially (~$3K) blows away any most budgets, beyond
having one's project butchered in the process. One must be very careful about
potential leaks with a flammable gas such as propane. Check about first to see
if there is a standard for getting your own installation approved by inspection
by a state CARB agency, for instance.
That being said, the operation of such a rig is rewarding, for the sake of the
aforementioned 10% discount that propane fuel enjoys compared to regular. It
should be discounted more: back in the '80's, propane as motor fuel was priced a
further 10% less than camper/grill fuel- that doesn't happen any more. I should
mention that milage on propane is mebbe 10% less, but the engine runs so sweet
and clean as oil contamination by carbon and unburnt fuel doesn't happen. I
seldom change the oil in my Ford, only add a quart as required, and the oil
filter seems good for a year at least. Engine wear is minute, proven by many
stationary engines running with minimal maintenance. Heavy road use means that
you should get newer hi-temp valve installed, as a gaseous fuel doesn't cool the
valves like gasoline does. For lighter recreation use, don't bother.
After 30 years, I have had to service the carb adaptor once, changed out one
fuel check valve for leakage, and tightened up fittings as required.
If you're still with me here, check online with www.ProPaneCarbs.com/ for more
info. He seems to have hardware and adaptors for any-sized engine, air or
water-cooled, and has been the most helpful, with good prices. I'm not
affiliated, just a satisfied customer. Hope this is useful. ;-}