I have a jd 240 mower [vintage 1989]. The mower started this season just fine! But started back firing and now it just won't start.

[charles.harward]

The mower started just fine at the start of this season. Then it started back firing on some restarts and now it will not start. I have looked at the fuel pump and it's fine. Looked at the carb bowl and it was clean although I did not clean the jets. Tried using start fluid to no avail. Didn't even try to start. Looked at the spark with a spark tester. It fires with no misses, bur the spark is yellowish. What do I do now?

 

[Bertrrr]

Pull the flywheel and look at your Key - sometimes when backfiring it will shear the key and throw it off time

 

[smallenginerepairs]

The mower started just fine at the start of this season. Then it started back firing on some restarts and now it will not start. I have looked at the fuel pump and it's fine. Looked at the carb bowl and it was clean although I did not clean the jets. Tried using start fluid to no avail. Didn't even try to start. Looked at the spark with a spark tester. It fires with no misses, bur the spark is yellowish. What do I do now?

check your valve lash and possible bent push rod.

 

[charles.harward]

Thanks all, I will look into both things when I get a chance. I looked at the relative position of the flywheel magnet, the ignition coil and top dead center of the piston. Where TDC is, the magnet are almost past the coil. It would seem the spark happened just before TDC. I don’t really know how the alignment should be. I'm just a beginner at this "stuff".

 

[Rivets]

Check to see if the oil level is high and the oil on the dipstick smells like gas.

 

[bertsmobile1]

Take the fastener off the flywheel and look at the keyways.
The 2 sides should align to make a perfect square.
If not the key has sheared
Your symptons are consistant with a sheared key as if not catastrophic the mower gets progressively harder to start and power output decreases till eventually the flywheel is so far out of position the mower will not start .
Usually this will have the 2 sections 1/2 apart ( like a Z )

Now there are other things that will cause the same symptoms .
But this one is easy to check .

 

[charles.harward]

Check to see if the oil level is high and the oil on the dipstick smells like gas.

Will check,

 

[charles.harward]

Take the fastener off the flywheel and look at the keyways.
The 2 sides should align to make a perfect square.
If not the key has sheared
Your symptons are consistant with a sheared key as if not catastrophic the mower gets progressively harder to start and power output decreases till eventually the flywheel is so far out of position the mower will not start .
Usually this will have the 2 sections 1/2 apart ( like a Z )

Now there are other things that will cause the same symptoms .
But this one is easy to check .

Will check tomorrow.

 

[charles.harward]

Will check tomorrow.

I checked the fly wheel alignment and it is correct.

 

[charles.harward]

Take the fastener off the flywheel and look at the keyways.
The 2 sides should align to make a perfect square.
If not the key has sheared
Your symptons are consistant with a sheared key as if not catastrophic the mower gets progressively harder to start and power output decreases till eventually the flywheel is so far out of position the mower will not start .
Usually this will have the 2 sections 1/2 apart ( like a Z )

Now there are other things that will cause the same symptoms .
But this one is easy to check .

Looks good., thanks!