FARM MOTORS 



357 



The Jump-Spark System. The jump-spark system does 

 not have any working parts inside of the cylinder, where they 

 are exposed to the high temperature there present. The 

 mechanism is such that 

 it is convenient to vary 

 the time of ignition when 

 this is used to regulate the 

 speed of an engine, as it is 

 in the case of the automo- 

 bile engine. The jump- 

 spark system requires the 

 use of an induction coil, 



Fig. 227. 

 parts of a 

 tion. 



Sketch showing the essential 

 jump-spark system of igni- 



which, when connected to 

 one of the usual sources of 

 electricity, increases the voltage to such an extent that when 

 suddenly cut off the new or induced current jumps a small 

 gap. The usual spark plug is only a provision for placing 

 this gap inside of the engine cylinder. Owing to the high 

 voltage of the jump-spark system, certain wires must be 

 very carefully insulated in order that the gap of the spark 

 plug shall be the path of least resistance for the current 



to escape. 



Testing. It has been 

 suggested that tests be 

 made with the make-and- 

 break system of ignition 

 to determine whether or 



Fig. 228. A jump-spark or induction coil HOt the System is in WOrk- 



ing order when trouble is 



encountered. A convenient way of testing the jump-spark 

 system is to remove the spark plug and lay it upon the 

 cylinder and manipulate the circuit-breaking mechanism by 

 hand. If a good spark be obtained, it may be assumed 



