Mower won't start

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  #1  
Old 08-16-12, 10:55 AM
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Mower won't start

My mower won't start and I need to know how the "Operator Presence Control Bar" functions. At the end of the OPCB cable is a wire that runs to the armature. I assume that when the OPCB is in it's "not-run" position there should be continuity from this wire to ground. I also assume that when I pull the OPCB that there should no longer be continuity between ground and the wire. Is this correct? With my VOM I have continuity between this wire and ground all the time. When I pull the wire off of the armature then my assumptions above work. I disconnected the plug wire and had same results so assume I do not have a shorted plug wire, sparkplug, or the wire running from the armature to the OPCB. Could the armature be shorted internally?
 
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  #2  
Old 08-16-12, 11:02 AM
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The OPCB or handle is a brake on most mowers and simply stalls the engine.
 
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Old 08-16-12, 12:37 PM
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This is definitely not a brake, there is an electrical connection of some kind. I believe it replaces the old system where you used to see a metal piece bolted to the head, you would push this against the spark plug to kill the engine. I believe (and would like a small engine repair person to confirm) that this OPCB throws ground to the armature, thus to the spark plug, killing the engine.
 
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Old 08-16-12, 02:29 PM
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It grounds the system to kill the engine. Something is out of adjustment or broken, keeping the system grounded.
 
  #5  
Old 08-16-12, 05:45 PM
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Leave it to me to have a simple brain fart.
The bar simply disconnects the grounded magneto. If the bar is not held, the hot (or positive side) of the magneto is grounded, turning changing it from a generator into a spinning mass of metal. No power equals no spark.
Not knowing the make and model of your mower, I'll assume itís the same general ideas as my B&S engine on my push mower and similar to the engine on the snow blower I rebuilt a couple years ago.
If you think the bar is at fault (or associated wiring), simply disconnect the wire attached to the head (normally black or green) and the spark plug should fire (provided everything else is working and the plug is not bad).

What would be useful is the make and model of the mower, when it was last run, and any other information.
In the original post, you do not give any real information other then the mower won't start and then go after the Operator present bar. Have you checked for spark, is it getting fuel (in the carb and in the cylinder)?

To put the spark plug (and magneto) off the issues list, with the help of another person, pull the spark plug out. Connect the spark plug wire to the spark plug. Touch the tip of the plug to a cooling fin or the engine block. Have the other person hold the handle down and slowly pull the motor over. If you see spark, odds are itís a fuel supply issue.
At this point, knowing when it last ran would be useful information as it could be bad gas, gummed up carb, bad gasket on the carb (less likely), plugged fuel line (or fuel supply shut off), the list goes on.

I'm not a small engine mechanic, but with real information, I can tell you how to make it run.
 
  #6  
Old 08-16-12, 06:50 PM
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Already checked for spark, none. If the armature is grounded there will not be any, that's what the bar is supposed to do--I think. Mower has been running fine all summer. Used it about a week earlier. I even tried starting fluid but nothing--which is to be expected with no spark. I am sure it's in this circuit somewhere. The bar is functioning properly--all it does it does is swing a piece of metal on its axis so it no longer touches ground. When you let go of the bar, a spring pulls the metal back and makes contact with ground--which then transfers ground along the wire to the armature. I believe--and that is my question--that this ground is what kills the mower. If so ground is staying on the armature all the time, regardless of the position of the bar. And as mentioned before, bar is functioning properly and there is no short on the wire running from bar to armature. My guess is that armature has failed and is always shorted. Mower make is not relevant (it's a Craftsman) but the engine is a "standard" B&S as you mention.
 
  #7  
Old 08-16-12, 07:18 PM
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Let me start over. Northern Mike I appreciate your help but I never asked "Why won't my mower start?" I guess I threw you off with my subject line. I asked two questions: 1. With the bar it "no run" position should there be a ground potential on the wire running to the armature? 2. With the bar in the "run" position should there NOT be any ground potential on that wire? With starting fluid in plug hole I ruled out fuel and I ruled out spark since the spark would have ignited the ether. I pulled the plug and held it to the head with my wife pulling the rope--no spark. Therefore my problem IS no spark. The bar and the bar's mechanism tested and passed. Wire tested and passed. If two above is correct then I am getting ground all the time to the armature--but it is not coming from the bar but from the other end--the armature. So what I want to know is the answer to 1 and 2 above "Yes." If so I need a new armature.
 
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Old 08-16-12, 07:21 PM
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Disconnect stop wire on coil and then check for spark, making sure plug is grounded if using it to check for spark.
 
  #9  
Old 08-16-12, 08:09 PM
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The wire going from the coil to the kill switch grounds to kill the engine when you release the handle. If you disconnect it from the coil and still have no spark, the coil is bad (assuming the air gap between the coil armature legs and the flywheel magnet is .010" or close to it). The wire will show some continuity to ground even if the coil is good.

Mike, it doesn't have a "hot" side to the coil or generator or power going to the coil.
 
  #10  
Old 08-17-12, 08:45 AM
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Thanks, that's what I was looking for. Your suggestion is the one I haven't tried yet. I did disconnect wire from coil to make sure there wasn't a short in between, there wasn't, VOM showed what I assumed--bar up no continuity, bar down continuity to ground. Did check gap and it's OK. Thanks again. Will test later, 80 mph winds last night so my challenge is elsewhere this morning.
 
  #11  
Old 08-31-12, 10:48 AM
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FYI Bad armature. New armature, now running like a top. Thanks everyone.
 
  #12  
Old 08-31-12, 10:02 PM
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Good news! Thanks for the update, and glad we could help.
 
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