from the March 1996 issue of the
Hercules Engine News
by Glenn Karch
In early November a call was received from Ohio in regard to a 3 HP Hercules engine with a natural gas fuel mixer. The engine had an H. M. Spence tag attached to it. I assumed that the engine was a hit and miss with the Hercules made LP/NG mixer on it. Later in the month, a call came from Petroleum, West Virginia, in regard to a 3½ HP model SK Hercules built engine. After some discussion, it suddenly became apparent that this was a throttling governed natural gas engine, which I had never heard about before. It, too, had the H. M. Spence tag.
Early in December my oldest son and I made a trip to Virginia and on the way back we detoured to Petroleum, West Virginia, to see the throttling governed natural gas engine. Sure enough, there it was. Simply put, it was an SK model with the kerosene mixer body and pump removed and a special natural gas mixer substituted in its place. The H. M. Spence Company must have provided a conversion kit. It consisted of an adapter that attached along with the throttle body to the engine head. Too, the adapter was fitted to the natural gas mixer. A cross section of the H. M. Spence mixer is illustrated here. It is interesting to note that Hercules also supplied a similar but smaller version of this mixer for hit and miss engines. It is attached to the regular type gasoline mixer that had a modified opening for the LP/NG mixer.