456 THE HANDBOOK FOR PRACTICAL FARMERS 



POUNDING: 



Ignition Spark too early. 



Motor 



Red-hot carbon deposit in 



cylinder. 

 Loose bearings. 

 Tight piston, due to lack of 



oil or lack of cooling water. 

 Hot bearings. 

 Loose flywheel. 

 Very loose piston (piston 



slap). 



BACKFIRING: 



Ignition 



Fuel 



Motor 



Spark too late. (If motor 

 backfires and stops, spark 

 may be too far advanced). 



Short circuit on primary wire. 

 [_ Wires to wrong plugs. 



rWeak mixture. 



1^ Occasionally too rich mixture. 



f Leaky or stuck intake valve. 

 J Red-hot carbon deposits. 

 I Leaky manifold or carburetor 

 1^ gasket. 



Insufficient lubrication. 



Insufficient cooling water. 



Circulation of cooling water 

 impeded. 

 Motor j Pump not working properly. 



Heavy carbon deposits in cyl- 

 inder. 



Water chamber coated from 

 impure water. 



IRREGULAR SPEED: 



r Loose connections, or partly 

 J •. • J broken wire. 



I Vibrator or breaker points 

 !__ pitted, or poorly adjusted. 



r Supply to carburetor irregu- 

 Fuel <^ lar. 



[ Dirt on needle valve. 



r Governor gummy, sticky, out 

 of adjustment or badly 

 worn. 

 Valves sticky. 



Motor 



SMOKE: 



OVERHEATING: 



Ignition Spark too late, or very weak. 



Fuel Mixture too rich. 



Black smoke in exhaust indi- 

 cates too rich a mixture. 



Bluish smoke indicates too 

 much lubricating oil. 



Smoke from the crank case or 

 open end of cylinder indi- 

 cates leak past the piston. 



Look for worn rings, rings 

 stuck in grooves, or scoring 

 on cylinder walls. 



