129 backfire & deck issues
 

Tonight I was mowing with one of my 129's and it runs as smooth as silk, until you turn the engine off and then it backfires. It has done this before and fouled a plug or two. I had both the low idle screw and fuel inlet screw adjusted to specifications and it backfired hard after about 20 min. of run time, so I opened them both up 1/4 turn and a week later (tonight) it backfired again, but not as hard. So, any recommendations (besides send my tractor to someone...LOQ, :biggrin2:).

Also, when I have the deck down on the lowest setting, the spindles roll to almost a stop and do not cut the grass. If I raise the deck up (3rd notch), then they spin freely. I only have two settings on my deck adjustment, low (1st notch) and high (3rd notch)-which doesn't cut the grass down below about 3 1/2". So, why do my spindles stop and how can I resolve this issue?

Thanks for your helpin advance!!

Cub Cadet 123

Backfiring issue... Check your timing. 90% of carburetor problems are electrical...

Mower deck: belt tension, especially on the spindle to spindle belt. The tensioner may be stuck.

Let us know how it goes!

Thanks Tyler, but if it was a timing issue, then why would it run smooth as silk until I shut down and then backfire. I have great range from high to low and low to high on the throttle, without any hesitation.....do you still believe it is a timing issue?

Cub Cadet 123

Have somebody watch the PTO and see what it's doing when the deck slows down. My bet is the PTO is worn or out of adjustment, and may need rebuilding. You would hear/smell a belt slipping.

Are you letting the engine idle before turning it off and are you turning it off at idle? If not, that's why you get the 'after-fire' every time you shut off the engine.

Matt, thanks for the heads up. Come to think of it, I am shutting it down at full or close to full throttle each time it has back fired. I guess I didn't consider that I was loading up some extra fuel for burn off before I shut it off, thereby causing the back fire issue.

I'll have to check the front PTO and the belt tension on the deck to see why I am loosing power to the pulleys.

Thanks guys,

Cub Cadet 123

DO NOT SHUT OFF AN ENGINE WITH OUT LETTING IT COOL DOWN FIRST!!! after working, say mowing for a while, let the engine sit and idle for a minute or two to cool down. You will not have any backfiring issues and it will last a lot longer.

This is good advice, it goes for all engines that are working under load.
things need a chance to stabilize, just like taking time to warm up a bit before going to full throttle.

Thanks for the tips fellas!!

Cub Cadet 123

Kinda deeper thoughts into the backfire already answered but after a hard run the exhaust is hot. Turning key shuts of spark so unburnt fuel enters the muffler and ignites. Could be a sign of running lean but I wouldnt worry about it. Briggs used a fuel solenoid on the bottom of the float to prevent this. When the key was turned off the solenoid would shut off the fuel supply from entering up in the carb. My guess briggs started doing that after emissions crap made them run real lean.

My thinking is you should run it a tad over idle or maybe closer to 1/2 to cool because of the flywheel fan wouldn't be blowing so much at complete idle. And I heard that is especially true to the 14hp because its based of the same block and cooling fan as the 10-12hp. :bigthink: Is this correct and do others agree?

They look the same, but the flywheel/ cooling fan/ fan shroud on a 14 hp is much larger than those found in the 301 12 hp (never seen a 241 in person, so I don't know if they are the same as the 301 or not).

From my understanding, they all cool the best at wide open throttle (more air flow). But for the back fire issue, I would reduce the throttle to idle for a few seconds before turning off the ignition...that should help.