Need Diagnosis help

[TomC]

I recently bought a used (2004, I think) Bolens 38" lawn tractor with aa 15.5 hp B&S engine for next to nothing. It needed a new carbeurator and battery, which I have now replaced. The mower cranks fine and runs fine without the blades engaged. Once the blades are engaged and it begins cutting, the mower will intermittently try to stall out. If you depress the Brake, the engine returns to normal. This will happen a few times in a row, but then it might cut for a few minutes before trying to stall again. After 10 or so minutes of this annoying issue, it seems to get more frequent until it is too frequent to continue. Oh, and when it tries to stall, it backfires, sometimes very badly.

My first thought is a Safety Interlock Switch is causing this, but I would have thought it would not be so intermittent or would not get worse with time. This mower does not have a seat safety switch and also will cut in reverse. Both of those features I thought were not possible due to safety switches, so I suspect the previous owner may have disabled both of those switches, if they did once exist.

I would appreciate anyone's insight into what I am dealing with and thoughts on what would be the most logical thing to try to get this corrected.

Thanks

 

[Fish]

It likely does have a seat safety switch, and that is likely where your problem lies. Post the model numbers off of the tag under the seat, and I will look at the blowup,
thanks

 

[Fish]

Likely the simple setup covered by 7-10, just unplug both wires and keep them from touching anything, and see if this helps..... Also, lift the panel over the shift levers, and make sure that the reverse wire/terminal is not loose and close to any metal as well...

 

[TomC]

Thanks, Fish. I will try that and see what happens.

 

[wjjones]

Thanks, Fish. I will try that and see what happens.

How short are you trying to cut the grass?

 

[TomC]

Wjjones, it does not seem to matter how low I set the cutting deck. If the blades are engaged, it will try to stall; if they are not, it runs like a top. Does not matter how high the engine is revved, either.
I think this has to somehow be linked to the blade engagement. I would have no problem reinstating the seat safety switch, but not sure how that would affect the issue I am having.

 

[wjjones]

Wjjones, it does not seem to matter how low I set the cutting deck. If the blades are engaged, it will try to stall; if they are not, it runs like a top. Does not matter how high the engine is revved, either.
I think this has to somehow be linked to the blade engagement. I would have no problem reinstating the seat safety switch, but not sure how that would affect the issue I am having.

Sounds like something is in a bind on the deck maybe the pto, belt, etc. Is yours the one that engages itself when you lower the deck? Check your mandrels/ deck spindles, and idler pulleys to see if one is trying to seize up, and the routing on the belt to make sure its in right.

 

[Fish]

The seat switch is just two sprigs of metal that are pushed together when the user lifts off of the seat, and are allowed to separate when the user is seated, sometimes the metal strip bend too close together, and when the blades/switch are engaged, the close metal will arc and sense that the operator isn't seated. Same goes with the wire to the forward/reverse lever.