12.5 riding mower engine stalling

DaveRosner · Jul 18, 2015

Hi

First time this season I tried to start my toro 12.5 riding mower with b&s vertical 12.5 engine. Starter would get stuck and seemed like it was seized. Took the cylinder head off and used a large wrench to get the engine to rotate. Put some pb blaster in the valve stems and cleaned the head real good including around the valves. Put it all back together and turns real easy now. Starter now works and it starts the engine.

Few problems Im now seeing...

- at full choke it stalls - so to start it I just have it at full throttle
- I was able to ride it around a bit at low speeds and reverse for a while but it was stalling at higher speeds
- today I took it out to use the mower - when I engage the mower it stalls
- I was able to put it in reverse to get it out of the barn
- now whenever I take my foot off the clutch/brake it stalls - any speed, reverse, even neutral

So it seems like either there isn't enough power/rpms so it stalls whenever I put a load on it. OR there is some kind of kill switch or electrical problem that causes the engine to cut off when I release the clutch/brake.

Any suggestions for trouble shooting?

lugnut1 · Jul 18, 2015

check the spark plug for fouling ( plug will give information on whats going on at times)
when was it changed last?
(plug maybe getting weak)

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Mikel1 · Jul 18, 2015

Air filter clean, carb may need cleaning

SeniorCitizen · Jul 18, 2015

DaveRosner said:
Hi

First time this season I tried to start my toro 12.5 riding mower with b&s vertical 12.5 engine. Starter would get stuck and seemed like it was seized. Took the cylinder head off and used a large wrench to get the engine to rotate. Put some pb blaster in the valve stems and cleaned the head real good including around the valves. Put it all back together and turns real easy now. Starter now works and it starts the engine.

Few problems Im now seeing...

- at full choke it stalls - so to start it I just have it at full throttle
- I was able to ride it around a bit at low speeds and reverse for a while but it was stalling at higher speeds
- today I took it out to use the mower - when I engage the mower it stalls
- I was able to put it in reverse to get it out of the barn
- now whenever I take my foot off the clutch/brake it stalls - any speed, reverse, even neutral

So it seems like either there isn't enough power/rpms so it stalls whenever I put a load on it. OR there is some kind of kill switch or electrical problem that causes the engine to cut off when I release the clutch/brake.

Any suggestions for trouble shooting?

To temporarily eliminate all safety kill switches as being the culprit, disconnect the magneto grounding ( kill ) wire on the side of the engine. It will be the wire that comes from the magneto under the engine cowling. Any chaffing on that wire ( bare spot ) will be the only thing that will then kill the mag. function other than mag. failure. To stop the engine, turn key switch off and touch that mag. wire back to its terminal or the engine metal.

DaveRosner · Jul 18, 2015

Great tips!

I disconnected the kill switch from the magneto and she runs just fine and no stopping. So when i engage the brake/clutch or the pto it kills the engine. Probably a bad switch somewhere that I should be able to debug.

Only remaining question - why would full choke stall the engine? She starts just fine with choke but it tells me something is amiss...

lugnut1 · Jul 18, 2015

(Only remaining question - why would full choke stall the engine? She starts just fine with choke but it tells me something is amiss... )

answer:
the choke is only mean't to start a cold engine, once started the throttle should be moved to the run position.
(engines will begin to run rough and eventually stall if left on choke)

SeniorCitizen · Jul 18, 2015

DaveRosner said:
Only remaining question - why would full choke stall the engine? She starts just fine with choke but it tells me something is amiss...

The normal air fuel ratio should be around 14:1 if I recall. When the choke is applied think of it as The Incredible Hulk with a grip on your throat cutting most of your air off. If continued very long you gonna die too. The choke function is to change the air gas ratio for easier starts when the engine is cold.

Your single cylinder Briggs seems healthy to me.

12.5 riding mower engine stalling

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