In the fall of 1916, Sears, Roebuck & Co. began offering engines that would burn natural gas, artificial gas or gasoline. As Picture #1 shows, these engines were advertised as available in all sizes. Unfortunately, the details of this gas attachment are not clear enough to see what it looks like, and they are not illustrated in any other literature seen so far.
Picture #1: 1916 Sears, Roebuck & Co. ad for Economy engines outfitted to run on natural gas, artificial gas or gasoline. No other literature showing this style of Economy engine has been found.
Earlier this year the opportunity came along to obtain the fuel mixer shown in Picture #2. It is nothing more than the common 'J' mixer used on the gasoline hit-and-miss engines, except it has a threaded port in the casting to screw something into it that has 3/4-inch pipe threads. I have never seen the gas attachment that screws in there, nor have I ever talked to anyone who has seen it. From what I can see in the catalog, it appears that some kind of horizontal gas attachment is screwed into the mixer at the same point.
Picture #2: 'J' style mixer with additional threaded port clearly visible. It's unknown if this mixer was originally made to equip Economy engines to run on natural gas.
Taking a clue from the later vertical-type gas attachment, I decided to try to make one, as shown in Picture #3. It is simply a hollow chamber with a seat and moveable gas valve in it that works against a weak return spring during the engine intake stroke. The gas supply comes in through a hand valve into the chamber where the valve is.
Now comes the big question. Does it work? W-e-l-l, it works, but not with the consistency I would like, so it's back to the drawing board and fiddling around with the gas pressure, gas adjustment and return spring tension. Surely somewhere out there someone has - or has seen - the genuine gas attachment for this kind of mixer.
Glenn Karch is a noted authority on Hercules engines. Contact him at: 20601 Old State Road, Haubstadt, IN 47639, or via e-mail at: firstname.lastname@example.org