50 hp johnson does nothing but backfire now and then

[tom2]

Hi,<br />I have a 1985 50 hp johnson that does nothing but backfire through the exaust every once in a while while cranking.. It was running great then the next time I went to start it this happened. Compression is 130 on both cylinders and has good spark.Could the ignition module be bad? I really can't see how the key way would slip just like that.<br />Thanks for the help<br />Tom

 

[DHPMARINE]

Re: 50 hp johnson does nothing but backfire now and then

Do a gas sample,and yes you have to check the flywheel key.<br /><br />Unless you want to replace parts then check the above.<br /><br />DHP

 

[jleus]

Re: 50 hp johnson does nothing but backfire now and then

There is easily eneough force (energy) to shear the key in half, long ways, with what seams like the mildest of lean spits or back fires, ......promise.

 

[Joe Reeves]

Re: 50 hp johnson does nothing but backfire now and then

Backfiring thru the exhaust is usually caused by a sheared flywheel key.... throws the engine out of time.<br /><br />The above is usually caused by someone having the flywheel off, then installing it without torquing the flywheel nut to 105 foot pounds.<br /><br />If this is the case, check the flywheel and crankshaft tapers, and clean them up if needed before installing another key.