Backfiring Thru Exhaust.

[minkota]

I have a 1988 Johnson 120, I just replaced the fuel pump and fuel lines and took it out for a trial run. all was going well when we realized we were low on fuel and headed in. I went for the truck and my son decided he was gonna putt around while I was gone. by the time I returned with the truck/trailer he was about 100 yards away from the ramp and I could see he was paddeling in. I assumed he had run out of fuel so didnt think much of it. tonight I refuel the boat and went to start it and it wouldnt start all it does is backfire out thru the exhaust. I am thinking it may have sheared the crankshaft key, does this sound about right, or is this just wishful thinking on my part? Thanks

 

[Joe Reeves]

Re: Backfiring Thru Exhaust.

That's what it sounds like. Be sure to clean up the flywheel and crankshaft tapers, install a new key and torque the nut to factory specifications.

Key flat edge must be installed vertically with the engine, not with the crankshaft taper.

 

[minkota]

Re: Backfiring Thru Exhaust.

That's what it sounds like. Be sure to clean up the flywheel and crankshaft tapers, install a new key and torque the nut to factory specifications.

Key flat edge must be installed vertically with the engine, not with the crankshaft taper.

Great, I appreciate the quick response. i will post my findings in a day or so. with the holiday I am not sure when the parts house will be open and i can get a replacemt key. Thanks again.

 

[minkota]

Re: Backfiring Thru Exhaust.

That was it. I sheared the key in half. I bought an extra one like 6 months ago for a spare and totally forgot I had it, but found it while getting tools out to remove the flywheel. Thank God I thought ahead of time to get a spare! Thanks again Joe.

 

[boobie]

Re: Backfiring Thru Exhaust.

Did you torque the flywheel nut to the right spec this time ?

 

[jay_merrill]

Re: Backfiring Thru Exhaust.

Just a minor point and admittedly a little "nitpicky," but when an engine fires through the exhaust, you have an afterfire.

A backfire is when it fires "back," through the intake/carb.



???

 

[wilde1j]

Re: Backfiring Thru Exhaust.

You will only get a few tries before destroying the flywheel and the crank if you don't get it right. Flywheel bore and crank taper must be clean and dry, nut MUST be torqued to correct value, or it WILL shear the key again and you may have garbage can material left.

You should never need a 'spare key', if done right.

 

[minkota]

Re: Backfiring Thru Exhaust.

Did you torque the flywheel nut to the right spec this time ?

Yes, 140-150# per service manual. I did 150.

Just a minor point and admittedly a little "nitpicky," but when an engine fires through the exhaust, you have an afterfire.

A backfire is when it fires "back," through the intake/carb.



???

I am aware of that, but the last time I used the term ?After fire? few knew what I was referring to so I just went with a known term ?Backfire?.

You should never need a 'spare key', if done right.

I replaced the Stator not long ago and noticed the ?Key was a little worn so I ordered it with plans to replace it but due to death in the family and having spent 6 months settling the estate the boat issues took a back seat and I forgot.