I recently bought a conversion kit to make my Troy Bilt Pony run off propane. The kit was AltFuel "Green Conversion kit for Small Engines Model 2." The company is in Toledo, Ohio, and you can find them online. There are other companies that you can google, too. Basically, it consists of 4 components: 1) a high pressure valve, to reduce the pressure from the tank, just like the one for your propane barbecue; 2) a shut off valve; 3) a low pressure demand regulator; (4) a conversion block or plate that goes between the carb and the engine intake port. Besides that, the only part that isn't an off the shelf item is the low pressure demand valve, which responds to demand from the engine. This demand is determined by the throttle. When you open the throttle, the engine intake vacuum increases, and the demand valve responds by delivering more propane. Just as the gasoline carb does when you open the throttle--it sucks more gas because you've increased the demand. The adaptor plate or block replaces the one on the Briggs engine, and is the same shape and size. It's machined out of aluminum. It has a port drilled and tapped in the side for the propane hose. This plate would not be hard to make if you had a chunk of aluminum. You might even be able to do it by drilling and tapping the plastic one that's already part of the engine, but I suppose there's a chance you might crack the plastic during the process. You do have the choice of drilling and tapping the carburetor itself, but that commits you to propane forever, as the carb is now ruined for gasoline. I opted for the other to retain the option of reverting to gas. I did remove the gas tank (easy to put back on if desired), and mounted the low pressure valve in its place. The kit is designed to use the throwaway bottles, but I already had a 5 lb. (1 gal.) tank which I can refill from my 20 pounder. Much, much cheaper and greener too! I had to get a different hose for that connection. Yesterday I tilled the garden to put it to bed for the winter. It worked great (except for a little tendency to pulse--haven't trouble shooted (shot?) that yet). The tiller started up pretty easily (quite cold, you know), and seemed to have all the power I needed. Why did I do this? Good question. Certainly not to save money. The kit was pricey, and there's no way I'll ever get my money out of it (but people buy expensive tillers all the time to grow $100 worth of vegetables). I mainly was just satisfying my curiosity. And now I won't have to do any carburetor rebuilds, worry about stale gas, and spew stinking gasoline fumes. So, has anyone else tried this? What problems did you run into? Would you do it again?