View Full Version : Riding lawnmower stalls when put in gear-???


thedelihaus
07-11-2010, 09:05 PM
Rebuilt the carb on my 12.5 HP Briggs & Stratton equipped Murray riding mower.

I did the rebuild correctly, I'm sure.

The mower idles fine at cold and also startup- dreamy.

However, when put under full gear load, it stalls.

In gear, releasing the combined brake/clutch pedal,the mower will move forward, slightly, but under full load, or full pedal release, it struggles to stay idling, then stalls.

I am quite sure I have the idle screws (top idle screw, and bottom float bowl screw) perfect- I know these mowers work best in between 3/4 to 2 1/2 turns (ideally set between 1 1/4 to 2 1/4 turns from seated).

Perhaps the float needle needs adjusting? I dunno, I'm a bit lost on this.

When I worked on these before, I never ran into issues. Same with when I worked on motorcycles.

But it's Ben six years, and some of my memory is scrambled. :thumbsdn:

whoaru99
07-11-2010, 09:22 PM
Governor hooked up correctly?

BruceRPA
07-11-2010, 09:36 PM
I had one of the spindle bearings go bad on the mower deck of my garden tractor and it caused the same problem that you are describing. It ran fine but would stall when the mower deck was engaged. That had me stumped at first.

Just something else for you to look at.

fotno
07-11-2010, 09:57 PM
Paul: You're talking about it stalling with just the transmission engaged, not the deck PTO right?

jimbofish
07-11-2010, 10:00 PM
IME that 'dreamy' idle may be at fault. You should have a narrow range where the idle doesn't change with the mixture screw, maybe 1/4 - 1/2 turn. Set the mixture on the rich side (CCW) of that range or just where it starts run a tad roughly.

thedelihaus
07-11-2010, 10:02 PM
Governor hooked up correctly?


I know shoot from shinola regarding governors. Could you tell me more?

Let me supply more info.

Runs like a top, until engaged in gear. New plug, new magneto, all new jets, new fuel line, fuel shutoff valve, cleaned tank, fresh gas, new fuel filter to keep carb clean. Float bowl cleaned and devoid of any rust.

I have the manual choke correctly hooked up (manual choke- old mower).


End of year last year it started sputtering and the person who drove the lawn mower needed to open the choke to keep it from stalling. Gas was low- possibly empty. But also-

I had purchased this running and with carb supposedly rebuilt- it ran but ended up quickly being temperamental- removing the float bowl greeted me with a bowl full of large rust flakes.


It was end of season, and I didn't do anything until this past week.

The magneto was visited by a mouse family, which chewed through the wire, partially. That has been replaced.

Mouse family was eaten by a snake, which then was caught under the engine shield, since it's belly was now full, essentially trapping the snake, which died. Snake and mouse remains cleaned from beneath engine shield.



Suggestions are a faulty seat switch, yet it only stalls under load, and not when put in gear. I think these seat switches stall the machine when put in gear as a safety measure.

This one however, stalls only under increased load- ie; to give enough "grunt" to move mower/rider forward or reverse, when gearing engaged, and only when clutch is fully released. Partial release will slightly move the mower, though you can tell it starts to want to quit.




Another suggestion is the float needle- perhaps it's not seating correctly? Perhaps the tab it sits on got moved during cleaning?

thedelihaus
07-11-2010, 10:04 PM
IME that 'dreamy' idle may be at fault. You should have a narrow range where the idle doesn't change with the mixture screw, maybe 1/4 - 1/2 turn. Set the mixture on the rich side (CCW) of that range or just where it starts run a tad roughly.

Mixture screw- to clarify, is it the bottom one on the float bowl?

I have adjusted it to no avail, but will surely give this a try.


Frustrating, as I used to get my carbs on my old cycles to work fantastic.

This simplified carb should be a walk in the park!

thedelihaus
07-11-2010, 10:05 PM
Paul: You're talking about it stalling with just the transmission engaged, not the deck PTO right?

Correct.:yes:

fotno
07-11-2010, 10:08 PM
IME that 'dreamy' idle may be at fault. You should have a narrow range where the idle doesn't change with the mixture screw, maybe 1/4 - 1/2 turn. Set the mixture on the rich side (CCW) of that range or just where it starts run a tad roughly.

Correct.:yes:

Ayup... I had a 12.5 Murray for years, and rebuilt the carb at one point. IIRC the manual recommends rough setting the mix screws at 1-1/2 turns out, and fine tuned from there a 1/4 turn at a time. Try that and see if it helps.

jimbofish
07-11-2010, 10:26 PM
The magneto was visited by a mouse family, which chewed through the wire, partially. That has been replaced.

Mouse family was eaten by a snake, which then was caught under the engine shield, since it's belly was now full, essentially trapping the snake, which died. Snake and mouse remains cleaned from beneath engine shield.

:pity: It's a tough world out there!

Suggestions are a faulty seat switch, yet it only stalls under load, and not when put in gear. I think these seat switches stall the machine when put in gear as a safety measure.


Possible... bypass the switch temporarily to be sure. There should be another switch somewhere that cuts those into the circuit when engaging clutch or PTO. But that would stop it like turning off the ignition and that doesn't sound like what's happening. :no:

jimbofish
07-11-2010, 10:32 PM
Mixture screw- to clarify, is it the bottom one on the float bowl?

I have adjusted it to no avail, but will surely give this a try.

Can't say without seeing the carb. If you can find the engine model #, I can check my B&S book for you.

The idle speed screw will be on or near the throttle parts. Idle mixture will be on the carb itself.

thedelihaus
07-11-2010, 10:43 PM
Ayup... I had a 12.5 Murray for years, and rebuilt the carb at one point. IIRC the manual recommends rough setting the mix screws at 1-1/2 turns out, and fine tuned from there a 1/4 turn at a time. Try that and see if it helps.

So far, it hasn't. A mechanic that works on these suggested as well to start outbas much as two full turns out, but you are correct- standard recommendation is 1 1/2 turns. I was told by a mechanic the bottom screw that resides in the float bowl is the one to worry about- and the top one for higher speed idle. Correct?

... bypass the switch temporarily to be sure. There should be another switch somewhere that cuts those into the circuit when engaging clutch or PTO. But that would stop it like turning off the ignition and that doesn't sound like what's happening. :no:

Correct- seems more like a fuel/air issue when under load.

Can't say without seeing the carb. If you can find the engine model #, I can check my B&S book for you.

The idle speed screw will be on or near the throttle parts. Idle mixture will be on the carb itself.


Yes- the idle mixture is one located in the bottom of the float bowl, the other on top of the carb just past the choke door, and in the tube-like body.

Thanks on checking your book for me- too dark now to give you a number answer, but it's an iron sleeve, manual choke, L head (no oil filter) single cylinder 12.5horse.

fotno
07-12-2010, 01:34 AM
So far, it hasn't. A mechanic that works on these suggested as well to start outbas much as two full turns out, but you are correct- standard recommendation is 1 1/2 turns. I was told by a mechanic the bottom screw that resides in the float bowl is the one to worry about- and the top one for higher speed idle. Correct?

It's been long enough since I've laid hands on one of these I honestly can't remember which screw does what; but if neither changes things enough that it will run under load, it leads me to think it's not an adjustment screw problem. At this point it could be a too rich or too lean float issue. If it were flooding, I'd think you'd smell the extra fuel and even at idle it would probably be chugging not idling smoothly. Too lean sounds way more likely. It probably idle okay, but start struggling as the load or throttle were increased. Too lean could mean that the needle and seat were opening too little, cleaning it up had floated a bit of debris into the seat, the needle was too long, the float lever was bent too far... Could be a lot of things.

It's not much help I know, but if I were stuck where you are I'd tear it down again and retrace my steps.

jimbofish
07-12-2010, 10:43 AM
Yes- the idle mixture is one located in the bottom of the float bowl, the other on top of the carb just past the choke door, and in the tube-like body.

Thanks on checking your book for me- too dark now to give you a number answer, but it's an iron sleeve, manual choke, L head (no oil filter) single cylinder 12.5horse.

The model # tells what carb is on the motor... they came in many configurations depending on the application. Should be a 6 digit #... the 3rd or 4th digit IDs the carb.

If that screw has no effect, there may be an air leak somewhere.

toxcrusadr
07-12-2010, 11:46 AM
Watching with interest. I have a gas powered weed whacker that does exactly the same thing. Starts and runs, but as soon as you rev it up and hit the grass (put a load on it), it stalls.

JBCobra
07-12-2010, 12:40 PM
adjust the bowl float. most likely need about a little clockwise. do while running at full tilt

drknstrmyknight
07-12-2010, 04:01 PM
Wild guess - is the muffler pulgged?

thedelihaus
07-12-2010, 08:23 PM
Muffler not plugged. Gas cap not clogged (the gas cap being clogged sometimes prevents proper fuel delivery)

whoaru99
07-12-2010, 09:31 PM
I know shoot from shinola regarding governors. Could you tell me more?



Only inasmuch as it's the mechanism that usually regulates the high idle, unloaded speed and also serves to open the throttle to "pour on the coals" when the engine speed drops due to increased demand/load. If the governor isn't working properly or maybe has become disconnected, the engine might seem to run fine until a load is put on it then fall on its face...at least that's my theory.

Generally, they're connected to the carb through a series of levers, linkages, and springs.

Ceallach
07-28-2010, 05:04 PM
Did you ever resolve this issue? I know L head Briggs like the back of my hand. I might be able to help you.

GordonW
07-28-2010, 05:17 PM
Paul, did you check the ignition timing? I have seen a rare case where a new magneto was indexed slightly incorrectly... when installed, the timing was retarded, and power was quite a bit down. Might act like this. Would idle OK, but would crap out as soon as power was required...

Regards,
Gordon.