Lawn mower misfiring/sputtering/deck jumping? ONLY when I engage the blades.

[milim05]

Hi, I have a Troy bilt Pony riding mower. When I turn it on and run the engine it sounds completely normal. High RPMS, low RPMS, top gear, slowest gear- all sounds/works as it should(I have noticed some very light/faint white smoke, maybe that could help determine the issue?). Then when I engage the blade, sporadically, the mower misfires/sputters or the deck is constantly engaging/disengaging. It sounds normal, then the problem occurs, then it goes away for a second, then it comes back. on off on off on off. Sometimes its normal for 2 minutes, bad for 10 seconds, good for a min. Other times its bad right after starting, "fixes itself" for a few seconds/30 seconds, then sounds bad again. I cant figure out what is causing the problem, why its happening etc. It has gotten progressively worse over the course of a month or so. I would rarely happen & i thought i was just clogged with wet grass etc but now its much more often basically preventing me from mowing without thinking something major is going to happen. Its only 1 year old!!!!

Things I have already done- Changed spark plug, changed air filter, changed fuel filter. I removed the blade brakes thinking they were constantly engaging when they shouldn't have been after I recorded a video of them appearing to bounce on/off. I checked the oil(recently changed, in spec). Took off the blades & checked for damage/something tangled around. Cleaned the entire underneath of the deck. Belt has slight wear but still appears mostly new. Pully wheels spin freely. Spring/wire that comes from the lever->deck that disengages brakes & engages blades appears normal? Electrical wires coming from deck lever appear normal? I dont know anymore. I also did the 2 things in the links below(vid 1 -my spring was on & appeared normal, vid 2- valves appeared in spec/not remotely close to what is seen in the video).

Troy bilt model #13AN77BS023 or #1003907068(picture included), serial number# 1E249B30399
with a briggs & stratton engine serial number# 1810191956677 model number# 31R9070062G1


All that i have done so far has fixed nothing. I have attached a google drive link to videos of what is happening/what it sounds like when the problem is occurring. As you can see in my longest video it sounds terrible, then it virtually disappears and runs normal, then it starts happening again. Its 100% sporadic/I have no idea when its going to happen. It is not affected by me pressing the brake to slow down, when I move the governor, when I go fast/slow, if i am in neutral or forward. Maybe i overlooked something, don't know what I'm looking at. I am losing my mind trying to figure this out. Please help lol

lawn mower - Google Drive

drive.google.com

 

[dougand3]

Good videos trying to diagnose. Try running in highest gear over low grass or asphalt W/O deck engaged - is there ANY engine stumble? Seemed it happened more when cutting higher grass, which is putting a higher load on the engine. Governor or partially clogged carb issue? And the basics - blade cutter is down? Blades are centered and secure on spindle shaft?
I'd pull deck off and examine spindle bearings/pulleys, tensioner pulley, belt travel position - correct side of keepers?

 

[Rivets]

I’m going down a different street and would like you to check the units drive belt and not the deck belt. Also check the idler pulleys and tensioner arm, make sure they are in good condition and moving freely. I know that this sounds odd, but want to eliminate other possible problems and narrow down the where the problem exists.

 

[EightWide]

You might have it. Ithink spark. Take off TVI resistor from plug wire & replace it with non res. type. If its not bad. it will be. Eightwide.

 

[Darryl G]

Have you checked/cleaned/tightened your battery terminals. It's acting like a low voltage condition in my opinion.

 

[bertsmobile1]

Firstly
The throttle has only 2 positions flat out and slowest idle.
Running at any other speed is bad for the engine , bad for the transmission and bad for the blades.
It can cause the deck to clog & put a high load on the engine which is running at a slower speed that maximum torque like it was designed to .

This can cause a carbon build up in the head.
The carbon build up glows red hot and causes the incoming fuel to ignite too early

Secondly the carb runs 90% on the starting jets until you put a load on the engine by doing things like going up a hill or engaging the blades.
This is regardless os what position you put the throttle lever in
This is why you hear the term "high idle" for the engine running at full speed ( around 3500rpm ) without any load.
At full speed under load then it shifts the other way up to 90% on the main jets.

At some point between the two situations you get to a changeover point where the bulk of the fuel supplies is shifting from the idle to the main jets & visa versa.
To me you have found that point and for some reason want to run your mower at it

Now if you have a carbon build up, it might clean itself if you start running at full throttle or it might need to have the head pulled and cleaned.

Also if you ave been using the mower at less than full speed the air flow has been drastically compromised and you have have cooked the head allowing the valve guides to shift.

 

[milim05]

Well, think we got it. Darryl G might be "the winner". Went to investigate the electrical wires/safety switch from engaging the deck lever and could not get to it without taking the entire frame off. So went to take the battery out and see if we could get to it from that angle. The battery has covers over the terminals and upon removing the covers, one of the nuts was basically off ?‍. Tightened up and ran it, seems to be working. Had to run out last night/raining today so wont get a full yard test for a bit but I think we got it. Glad it was something "stupid". Will post if any further issues & thanks for all the replies!

 

[Darryl G]

Well, think we got it. Darryl G might be "the winner". Went to investigate the electrical wires/safety switch from engaging the deck lever and could not get to it without taking the entire frame off. So went to take the battery out and see if we could get to it from that angle. The battery has covers over the terminals and upon removing the covers, one of the nuts was basically off ?‍. Tightened up and ran it, seems to be working. Had to run out last night/raining today so wont get a full yard test for a bit but I think we got it. Glad it was something "stupid". Will post if any further issues & thanks for all the replies!

Fingers crossed. It was the PTO disengaging along with sputtering that made me think that. Good detailed descriptions of the issue help a lot. Not something we often get here.

 

[Darryl G]

Well, think we got it. Darryl G might be "the winner". Went to investigate the electrical wires/safety switch from engaging the deck lever and could not get to it without taking the entire frame off. So went to take the battery out and see if we could get to it from that angle. The battery has covers over the terminals and upon removing the covers, one of the nuts was basically off ?‍. Tightened up and ran it, seems to be working. Had to run out last night/raining today so wont get a full yard test for a bit but I think we got it. Glad it was something "stupid". Will post if any further issues & thanks for all the replies!

Have you had a chance to run it to confirm it's fixed yet? I'm anxious to claim my prize.