Back fire under full load

[peter255]

I have a riding mower with a 17hp Intek OHV. The engine will start and run fine sitting still with the blades engaged. As soon as you start traveling to cut grass it starts backfiring. I took it to my local repair facility and $250.00 later they still don't know what's causing it. Any idea's on what could be causing this to happen? Thanks for your help!

 

[mistermowerman]

I have a riding mower with a 17hp Intek OHV. The engine will start and run fine sitting still with the blades engaged. As soon as you start traveling to cut grass it starts backfiring. I took it to my local repair facility and $250.00 later they still don't know what's causing it. Any idea's on what could be causing this to happen? Thanks for your help!

Hello, something that is worth checking is your seat switch or bag switch or any other switch that is part of the blade safety circuit, in my experience engine runs fine with blades engaged until movement of the mower causes a safety switch to make or break a connection causing a back fire on the engine.Gary

 

[Scrubcadet10]

First, i would remove the spark plug and see what color the electrode end is, black? white? brown?
I would run it and mow with the ignition coil kill wire unhooked, remove the top plastic engine cover, trace the spark plug wire and you'll find the coil, there should be a smaller black kill wire going to it, unplug it, reassemble and start it and mow, if it doesn't backfire and act up, the problem is probably like Mr.Mowerman said (keep in mind you won't be able to shut the mower off with the key with it unhooked,), if it still backfires it might be a fuel related issue, i have heard lean running can cause backfires.

 

[peter255]

Hello, something that is worth checking is your seat switch or bag switch or any other switch that is part of the blade safety circuit, in my experience engine runs fine with blades engaged until movement of the mower causes a safety switch to make or break a connection causing a back fire on the engine.Gary

Thanks for your input, Gary. I can sometimes run the mower up to 3 or 4 minutes before it starts backfiring and then after a few backfires it stops and runs fine and then randomly starts backfiring again. I did check the seat switch seams to be ok. the weird thing is that sitting still running with blades engaged it runs great, no problem at all. but after you start mowing for a few minutes start acting up.

 

[Hammermechanicman]

What did the shop do for $250?
Worn valve guides ,Manifold leak, high speed metering circuit in carb, weak coil, bad spark plug can cause random backfiring under load.

 

[bertsmobile1]

Take the blower housing off and remove the kill wires from the coils.
check that the mower still shuts off ( carb solenoid will do this )
Refit the blower housing then do a test mow.
Problem goes away = a fault in the safety switch circuit ( as previously pointed to )
Problem stays = internal engine problem

Let us know how it goes
And please remember this is for diagnosis only.
Your mower is now in a state where it is dangerous to itself and to you

 

[peter255]

Take the blower housing off and remove the kill wires from the coils.
check that the mower still shuts off ( carb solenoid will do this )
Refit the blower housing then do a test mow.
Problem goes away = a fault in the safety switch circuit ( as previously pointed to )
Problem stays = internal engine problem

Let us know how it goes
And please remember this is for diagnosis only.
Your mower is now in a state where it is dangerous to itself and to you

Thanks to everyone for your input. After starting the mower I disconnected a quick connect located just above the battery that looked like it connected to the blade kill switch and she ran fine. Once I have time I will narrow it down to which wire it is. Thanks again.