Over the years that I have been involved in the propane business I have been approached many times with questions about propane carburetion problems, especially on farm tractors. While there are a few occasions when the problem can be accountable to the LP fuel system, more often it is a combination of several small mechanical engine problems leading to some false conclusions about the real cause.

It is easy to blame the propane carburetion since it is a bit of an unknown to many or even most mechanics. If something is a bit of a mystery it usually invites suspicion, so I thought I would give a rough outline explaining the basics of the entire propane fuel system. Knowledge is power and in this case may be the power to think through and troubleshoot some of the engine problems that can occur with propane fuel.

To start with the fuel itself, propane or liquefied petroleum gas (LP gas) is mostly refined out of raw natural gas although a smaller amount comes from the refining of crude oil. It has a boiling point of about 44 below zero, an octane rating of 130 and is stored as a liquid under pressure in a heavy walled tank. Normal pressures in the fuel tank would vary from about 50 to 150 pounds per square inch depending on the temperature of the fuel in the tank. Higher temperatures mean higher pressures.

When burned, propane only has about 90% of the heat energy as gasoline, however, by raising the compression ratio and running a more open and cooled intake manifold with no heat riser, most LP fueled tractors meet or exceed the power output of their gasoline counterparts.

Order Issue #20 to keep reading this article.