john deere 40 won't start bad coil

nickkalisz

New User
hi i have a john deere 40 and it won"t start now. it cranks but no firing. i have timed it. there is spark. gas on. i was wondering if it could be the coil?. i was having problems before where it was running on 1 cylinder and it would bog down and have no power and the throttle would go back up again.
 
You say it has spark!!! And if its producing a spark the coil isnt the problem.. Where is that "spark" you say its producing???

If you get spark say from out of the HV coil wire but none to the plugs, its a cap or rotor or plug wire problem.

If you work through my Troubleshooting Procedure linked below it will help diagnose the casue of non firing, but if its producing a good spark, the coil is NOT the problem, you just have to get it routed from the coil out to the plug wires and thats the job of the distributor cap and rotor etc and then via the plug wires to the plugs.

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=665110

John T
John Ts Ignition Troubleshooting
 
Sometimes you can have a spark...like when taking
a plug wire off, and holding it near the block
while turning the engine over...BUT...the plug
won't fire under compression. You've got some
spark, but not hot enough to fire! Condenser or
coil are weak!
 
Cant guarantee its accuracy, but I read somewhere an arc of 3/16 inch in free air is approximate to an arc of 0.025 inside the cylinders at 100 PSI or so. Therefore, if the spark at 3/16 appears good and blue outside the tractor, it ought to be sufficient inside under compression.

Trouble is we have no idea what or where or the quality of the spark or gap he has when he says he "has spark"

John T
 
Check your sparkplugs to see if they're wet. You may not be getting fuel into the engine if they're dry. Hal
 

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