396 PRODUCTIVE FARMING 



retor which allows the suction of the piston to draw in both 

 fuel gas and enough air with each stroke. The temperature 

 greatly influences the amount of fuel gas and so more fuel is 

 usually supplied during the first few strokes when the engine 

 is starting and becoming warm. 



Abundant moisture in the air also slightly affects the mixt- 

 ure and some little adjustment may improve the mixture 

 when the weather is unusually wet or dry. The beginner 

 should usually let the carburetor mixture alone after the 

 engine is running and is fairly warm. He should know 



FIG. 249. Tractor used in hauling manure spreader. (Tennessee Power Farming 



Review.) 



that the carburetor is extremely sensitive and that a very 

 slight change in its adjustment is very effective in chang- 

 ing the mixture. 



The amount of unburned fuel which appears as black 

 smoke from the exhaust pipe is usually controlled by having 

 a proper mixture. One part of fuel gas to four parts of air is 

 a very rich mixture and may produce considerable smoke 

 under ordinary temperature and moisture. One part to 

 twelve or fourteen is called a very lean mixture and would 

 have too little power for an engine at work. 



Good compression is necessary so that the full power of 

 the fuel will be obtained. Piston rings are placed around the 



