cub lawn tractor backfiring?

[liammulloy]

My neighbor has a mid 2000's cub lawn tractor and any time he mows the lawn and then turn the tractor off with the key...5 or so seconds...pop. I have been working on lawn tractors for a while but don't know why its doing this. He wants me to fix it, what should I check first? He says the sparks are new last year. Someone told him to kill it with the choke and that seams to work, but is that bad for the engine?

Liam

 

[liammulloy]

also its a kohler engine if that helps at all

 

[drifter2518]

Shut tractor off at half throttle. States this in owners manual.

 

[liammulloy]

Shut tractor off at half throttle. States this in owners manual.

is that b/c its a kohler, I have a b&s v twin and its never done this. Thought that is might be something with the muffler.

 

[Baby Grand]

Sounds like enough fuel is left in the cylinder on shutdown to touch off after a brief soakback period.

Drifter2518's proposed half throttle fix makes me think this may be the cause and sounds like a very likely solution.

Give it a try and let us know if it works!

 

[Bird]

I currently have a Toro ZTR with a 15hp Kohler. The manual says to move the throttle between Fast and half throttle before turning off the key. The dealer says full throttle or at least 3/4 throttle. Now all my long life, I was accustomed to idling an engine before turning it off, but that's the wrong thing to do now-a-days. If you idle this engine and turn off the key, you almost immediately get a very loud, very severe pop. Lately, I've been sometimes (most, but not all the time) getting the delayed pop you described; 3 to 5 seconds after turning off the key. I just talked to my dealer about it day before yesterday. He says it will be the fuel shut-off solenoid sometimes sticking, but he also says it won't hurt anything (I'm not entirely convinced about that).

Incidentally, in 2004 I bought a Toro ZTR with a Briggs & Stratton engine. The solenoid never stuck on it, but you turned the key off at full throttle or you'd get a big enough pop to wonder if it would blow the muffler off.

So, my guess is that your friend's Cub Cadet has a faulty fuel shut-off solenoid.

 

[liammulloy]

I currently have a Toro ZTR with a 15hp Kohler. The manual says to move the throttle between Fast and half throttle before turning off the key. The dealer says full throttle or at least 3/4 throttle. Now all my long life, I was accustomed to idling an engine before turning it off, but that's the wrong thing to do now-a-days. If you idle this engine and turn off the key, you almost immediately get a very loud, very severe pop. Lately, I've been sometimes (most, but not all the time) getting the delayed pop you described; 3 to 5 seconds after turning off the key. I just talked to my dealer about it day before yesterday. He says it will be the fuel shut-off solenoid sometimes sticking, but he also says it won't hurt anything (I'm not entirely convinced about that).

Incidentally, in 2004 I bought a Toro ZTR with a Briggs & Stratton engine. The solenoid never stuck on it, but you turned the key off at full throttle or you'd get a big enough pop to wonder if it would blow the muffler off.

So, my guess is that your friend's Cub Cadet has a faulty fuel shut-off solenoid.

don't know why but i can turn off mine at full/half/idle (or some combo of the 3) and have never gotten a backfire, idk. You know why? or which is better?

 

[Bird]

don't know why but i can turn off mine at full/half/idle (or some combo of the 3) and have never gotten a backfire, idk. You know why? or which is better?

I'm sure not much of a small engine mechanic, so I can't say which is better. I preferred idling the engines before shutting them off. I think the idea of a fuel shut-off solenoid was to prevent the possibility of a carburetor float sticking and letting fuel either run out or run into the crankcase. But why it doesn't work at idle, I have no idea. I found and downloaded the Service Manual for my Kohler and to quote a small part of it:

Many engines are equipped with a fuel shut-off
solenoid installed in place of the bowl retaining screw

to eliminate back​

​

firing when the engine is shut down.​

If backfiring occurs on engines equipped with this
solenoid, verify that the correct shutdown procedure

is being used. In order for the solenoid to be e​

​

ffective,​

the engine must be running between half and full
throttle when the key is turned off. Next, check the
battery to ensure that it is not discharged or faulty. A
minimum of 7.3 volts DC is required to activate the

solenoid. Also check to see that the ground lead from

the carburetor body to the air cleaner base mounting​

screw is properly connected.