JOHN DEERE 318 LAWN TRACTOR WONT START

Here's the link and I'm sure you will get the solution of your problem.
John Deere 316 318 and 420 Lawn and Garden Tractors Service Manual

a weak spark indicates a coil problem
that problem can come from a faulty condenser in the ignition system or incorrect timing for the system
if it has an electronic ignition system test / replace it
if it has a points system replace the condenser and set the points to the correct gap
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Drain gas completely from tank to ensure no water is in the tank, check for spark with spark tester, if no spark shows with spark tester, re check gap on coil, if points & condenser are present, sand down the gap between the points to ensure a proper connection. Make sure to change fuel filter with a high quality John Deere fuel filter and use fresh fuel... Fuel can "go bad" after 1-3 months, if the tractor is/ left outside chances are there is water in the tank.

At that age, it's highly likely that there aren't any! You don't say what engine is fitted, but if it's a Briggs or a Tecumseh, they went solid state in 1982. If that's the case, just replace the coil module.

If your tractor has an anti back fire solenoid in the front of the carburetor then it should start if you remove it and cap it off with a pipe plug.It should run if the solenoid is the problem,if so you really should replace it but if it is'nt prone to backfiring with it remove you don't have to.You may also have a bad seat switch,confirm this by jumping the plug with a piece of wire to temporarily test it.

We will be testing for voltage to the points, coil, engine to tractor wiring harness, ignition switch

Tools needed:
volt meter to read 12 volts, or test light

1) with the points open: is there voltage at the connection wire at the points
If yes; adjust points to .020" and try to crank engine and check for spark
*** you may want to determine if condensor is connected to this wire also
if no
2) check point side (neg or - ) of coil for voltage
if yes, engine should start
if no
3) check for voltage at the + side of coil
If yes, coil is bad
if no
4) check wire connector from engine to frame wiring harness
if yes; engine should start

if no
5) check wiring on the back of ignition switch
if yes; engine should start

if no
6) check that ignition switch RED or BATTERY supply wire has voltage
if yes; switch is bad

if no
7) check supply wire and circuit breaker connected to the battery side of the solenoid
if yes; engine should start

if no; circuit breaker could be at fault or wire connector at battery supply

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May be the coil is bad. have you checked the spark plug? If there is gas and spark then it will have to start.check the circuit breaker points. is there current in the cb points?

did you make sure the gap was set right on coil & flywheel it should be .020 between magnet on flywheel & the coil & the same thing with the points in the open possition between points & condensor

Check the coil impedance on the primary and secondary side. You'll have to disconnect the battery negative cable so you don't short something out. Unplug the spark plug wires and the two sets of smaller wires connected to the primary side of the coil. The primary coil reading should be between 3.7 ohms and 4.6 ohms while the secondary (spark plug side) should be between 34.2 k-ohms and 41.6 k-ohms. If the resistance values you measure are outside of these ranges, you need to replace the coil.

The electro-magnetic coil side of your PTO is shorted out.On the 318 it is very easy to replace,just under front screen.