3/8 Report of the Horticultural Department of the 



not gummed up. It should be kept clean else the spark will not be 

 strong enough to ignite the gasoline. Be sure that the gasoline has 

 no water in it. Even a few drops of water will stop the engine. 

 Then if the engine is being properly fed and the current is strong 

 enough to ignite the gas, there must be an explosion in the cylinder 

 and the engine must go unless something is wrong with it other than 

 the feed. 



Back-firing may take place, in which case it is accompanied by 

 sharp explosion and jet of flame from air inlet, which results from 

 the charge igniting before entering the cylinder. This is usually 

 caused by bad mixture of air and gas. A leaky inlet valve some- 

 times gives the same difficulty. If this occurs during compression 

 it is usually due to wrong timing of the sparking mechanism or bad 

 mixture of gas and air as above stated. See that the adjustments 

 are corrected. • 



Any leak in a valve around a gas engine is sure to cause trouble^ 

 be it inlet or exhaust. If in the exhaust it will greatly lessen the 

 efficiency of the engine. If in the inlet valve, new mixture is coming 

 in all the time and will be forced back into the feed pipe during 

 compression, together with a part of the burnt gasses and eventually 

 this clogs the engine. 



Keep all parts clean, — valves, sparking mechanism, etc. See that 

 contact points are not corroded or furred with soot or carbon. Use 

 plenty of oil. But if too nmch oil is used the sparker becomes 

 corroded or furred. 



Be sure that the air supply is properly regulated. If the air is 

 cut ofif neither the vapor nor the liquid can be ignited ; if too much 

 air is present the mixture will not explode. If too much gasoline is 

 admitted it burns with smoke and does not give good pressure. 

 There should be just enough air to give sufficient oxygen to cause 

 complete combustion of the gasoline vapor. With standard gasoline 

 this varies in proportion from 6 to i to lO to i, according to con- 

 ditions. 



