25hp johnson backfiring - used to run then quit

[wheresthefish]

hello, i am looking to purchase this 25 hp johnson from around 1985. the person selling it said that it ran good one day then the next day it didnt start and would only backfire. does anyone know what could possible cause this? at least somethings i could look for before purchasing motor. i am willing to repair some minor things but nothing major, like changing pistons, etc.

 

[offshore100]

Re: 25hp johnson backfiring - used to run then quit

Sounds like a timing issue, likely a sheared woodruff key holding the flywheel in position on the crankshaft.

 

[wheresthefish]

Re: 25hp johnson backfiring - used to run then quit

i am not familiar with this part. is this is expensive fix? can you describe this part a little more. where is it located and how it looks. thanks alot.

 

[offshore100]

Re: 25hp johnson backfiring - used to run then quit

I won't go into great detail, use what i said above and do some research.
Good news is, should be dirt cheap to fix, you'll just have to pull the flywheel to see if that's the problem. Good luck.
That's a great motor, by the way, when it's right.

 

[F_R]

Re: 25hp johnson backfiring - used to run then quit

Flywheel: The thing on top that goes around when running.

Crankshaft: The main piece of the motor. Extremely expensive.

Woodruff key: A half-round piece connecting the two above items in precise alignment.

Buyer Beware: What you better do. Often when the flywheel runs loose (reason for shearing the key) it batters the slots that it fits in in the flywheel and crankshaft, destroying any hope of alignment.

Result: Junk.

But it might be something else. Like crossed spark plug wires. Feel lucky?