1972 40hp Johnson,coil problem ?

[Saboat]

Just trying to narrow down the problem.Did a carb rebuild and decarb after testing the motor and having firing problems.Motor ran fine on WOT for about 20 mins then went to 1 cylinder with no backfire or miss or any other warning.Have not checked the coils for cracks yet.Could this problem only be coil related ?

 

[petrolhead]

Re: 1972 40hp Johnson,coil problem ?

Could be the coil insulation breaking down as it gets hot.

 

[lark2004]

Re: 1972 40hp Johnson,coil problem ?

Check your vacuume cutout switch (if fitted), it grounds one coil only. if faulty, the coil connected to it won't fire.

 

[Saboat]

Re: 1972 40hp Johnson,coil problem ?

Had to take the motor to a dealer to have the flywheel pulled after trying for weeks of soaking and breaking bolts.Both coils were badly cracked and showed signs of burning so were replaced.That done,I now have a nasty backfire when starting.Could the timing or incorrect point gap cause this ?

 

[Chinewalker]

Re: 1972 40hp Johnson,coil problem ?

Hi Saboat,<br /> Were the plug wires placed back on the correct plugs? On the Johnrudes, the front coil fires the top cylinder.. There should be a small metal or plastic ring on one of the plug wires with the word UP on it. If the wires were replaced, the clip may or may not have made it back on the right wire.<br /> Over choking can also contribute to a backfire if the crankcase has too much fuel in it.<br />- Scott