Welcome to the DoItYourself Forums!

To post questions, help other DIYers and reduce advertising (like the one on your left), join our DIY community. It's free!

No spark Craftsman Lawn Tractor


Paul827's Avatar
Member

Join Date: Mar 2007
Posts: 7

03-26-07, 06:02 AM   #1  
No spark Craftsman Lawn Tractor

I have a Sears Craftsman Lawn Tractor (917254860) with a Briggs and Stratton TwinCylinder Opposed Engine. The engine turns over but will not start. I checked for a spark and found that I did not have one.
The problem arose after I cleaned out debris from the tractor. I am suspecting that I pulled a wire loose.
My reading suggests that I should check the safety switches. How is this done? I have a multimeter. I read in another forum that I could disconnect the cut off wire to the coil and then test for spark to determine whether the problem is in the safety switches. How do I locate and identify the cutoff wire?
If it is not a safety switch, what should I try next?
I don't have much experience troubleshooting electrical systems, but I am willing to learn. Thanks for any help.
Paul

 
Sponsored Links
Azis's Avatar
Visiting Guest

Posts: n/a

03-26-07, 06:27 AM   #2  
Azis
If the starter engages and spins then its not likely a safety switch. There is only one wire to the coil and should have a terminal or connector. The engine shroud will need to be removed to access the coil. Disconnect the wire and test for spark. If no spark with the wire disconnected then the coil needs replaced.

 
Paul827's Avatar
Member

Join Date: Mar 2007
Posts: 7

03-26-07, 07:30 AM   #3  
follow up question

Two quick follow up questions. When you refer to the "coil" is this the same thing as the part's diagram calls the "armature-magneto." (I'm looking at parts diagram for B&S Model 422700.
Second, I am concerned that I might have pulled or broken a wire in the ignition wire harness. The problem arose after I was removing debris from the tractor and I may have pulled the wiring harness as I was doing this. Its an old tractor (1992) so some of the wiring might be brittle. How do I double check the wiring harness? I assume I need to check for continuity at various points. Is that what I need to do and how do I go about doing this?
Thanks
Paul

 
Azis's Avatar
Visiting Guest

Posts: n/a

03-26-07, 09:17 AM   #4  
Azis
Yes the coil is the same as the magneto.
Unless you have a wiring schematic, for the mower not the engine, your going to find it hard to ring/ohm out the harness. There are a few main connectors you can follow the harness to and check out the connections.
Where were u pulling debris from? There is not much under the mower that should cause no spark that I know of. And at least my experience with loose connectors has shown the opposite of no spark being the kill circuit does not work.
Unfortunately I feel the quickest troubleshooting step would be to confirm that the magneto is indeed working. You can also confirm if the kill circuit is working by checking the wire to the coil/magneto to see if has continuity to ground with the key off and open when the key is run. If the kill circuit does not open, then you can start the (possible) LONG process of illimination.

 
Paul827's Avatar
Member

Join Date: Mar 2007
Posts: 7

03-26-07, 10:23 AM   #5  
follow up

Thanks for the information. I'll probably be able to follow up on your suggestions later this week and will let you know what I find.
I purchased the tractor used. I was removing debris from the area above the deck near the stearing column right behind the engine. It is an enclosed area. The wiring harness runs through the area so that is why I am concerned about it.
I do have a parts diagram of the electrical wiring components of the tractor that I pulled off the Sears parts website. It gives me a decent idea of how the thing is wired, but it is not a detailed wiring chart.

Thanks again. If I get stuck I'll post another update.
Paul

 
Azis's Avatar
Visiting Guest

Posts: n/a

03-26-07, 11:34 AM   #6  
Azis
The pedastol or console area you mention is where you may find one of the main connectors. Follow it back from the key switch and you should see it. Also your safety switch for the clutch may be in that area along with its connections.
I agree it sounds most likely a result of your preventitive maint. however a faulty ground is hard enough to locate without it not even being there

Somewhere you may be able to find a schematic of your key switch or maybe just figure it out to verify its not the problem.
If you can list the letters on the back of your key switch, I bet some of these guys can tell ya how it should wring out from memory .

 
Paul827's Avatar
Member

Join Date: Mar 2007
Posts: 7

03-27-07, 07:28 AM   #7  
follow up

I tested for spark with the kill wire disconnected. I did not get any spark on either plug when I grounded the spark threads against a cooling fin. I also tested the kill wire for continuity to ground when the starter switch was off. I found continuity. As I understand, these tests establish that the coil is bad and needs to be replaced.
Also when I was inspecting wiring harness I found what appeared to be a previous repair to a black wire that was covereed with electrical tape. The repair looked as if it were coming loose so I will redo the repair. If I understand how this all works, a bad connection in the black wire might cause the safety shutoffs to fail to function, but would not cause the no spark condition. The no spark condition would in any event not be related to the possible wiring harness issue as the above tests completely isolate the coil from the the other electrical components. Is this understanding correct? Should I redo the repair before buying a new coil?
Thanks for your assistance. If I can fix this on my own, it will certainly save some money


Last edited by Paul827; 03-27-07 at 07:30 AM. Reason: added additional sentence
 
Azis's Avatar
Visiting Guest

Posts: n/a

03-27-07, 08:44 AM   #8  
Azis
Correct: Removing the kill wire from the coil isolates it from the rest of the circuit.
The seat switch I think is the only safety that would cause a no spark, however it would also not allow the starter to engage. The clutch and PTO safety I believe only cut out the starting circuit, but I would need a schematic to verify that.
The black wire, if it is indeed your kill wire, could cause the no spark if it were grounded out IE: pinched, bare wire touching frame...
Removing it at the coil eliminates it as causing the coil NOT to fire. I would indeed repair any wires you find in need.
You should also be able to confirm the kill circuit by ohming it with the key in the run position, it should not show continuity.

 
Paul827's Avatar
Member

Join Date: Mar 2007
Posts: 7

03-27-07, 09:00 AM   #9  
follow up

Right. The kill wire shows no continuity when starter switch is on.

 
Azis's Avatar
Visiting Guest

Posts: n/a

03-27-07, 09:11 AM   #10  
Azis
Good then all should confirm the coil as the problem.
It may be possible that if there is bare wire, and it is your kill wire, if your solenoid is under the console, perhaps it brushed against the hot wire or...

 
Paul827's Avatar
Member

Join Date: Mar 2007
Posts: 7

03-28-07, 10:04 AM   #11  
follow up

Posted By: Azis It may be possible that if there is bare wire, and it is your kill wire, if your solenoid is under the console, perhaps it brushed against the hot wire or...
I appreciate the time you are taking to educate me. Just so I understand your last comment, would it fry the magneto if a hot wire came into contact with a bare kill wire? One of the things that I am wondering about is what causes the magneto to go bad. I don't want to install a new one and burn it out. Is there anything I should be looking for to make sure there are no conditions that will cause the new magneto to fail.
I plan to buy a new one today and install it this weekend.

 
Azis's Avatar
Visiting Guest

Posts: n/a

03-28-07, 11:05 AM   #12  
Azis
That could very easily damage the coil. The coil part of the magneto is small gauge wire and while it does carry very high voltage, it carries very low amperage. Your DC voltage is only 12V but can deliver high amperage in the case of cranking your starter motor or a direct short to ground.
Coils can and do break down over time from elements of their environment, heat being the main thing.

 
Search this Thread