# No spark to plug on 12HP BS engine



## BillM2 (Oct 14, 2007)

I have a Briggs 12Hp engine (model 28407; type 1026-E1; code 980205ZA) on a Sears Craftsman Lawn Tractor (Model 917254520) and I don't have a spark to the spark plug. I've replaced the solenoid, the starter and the battery has a full charge. When I turn the ignition key, the engine's flywheel just spins and spins. When I have turned the engine over, I've held the wire close to the tip of the plug and I see no spark (nor feel anything through the insulation). 

I am reasonably handy but no mechanic so please bare with me. Anyting electrical I have a mental block about. I have a repair manual and it seems to suggest a magnetron and coil problem??? But don't let me suggest whar the problem could be.

I know where to order parts so don't necessarily need that information but part numbers would be helpful.

:thumbsup:


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## glenjudy (Aug 26, 2006)

Thus far in my experience with lawn mower engines, the only ones that suddenly come up with magneto/coil failure are these 12hp Briggs. Sounds like this might be your problem. Take the model/type/code to any authorized B&S shop and they will have it, or can order it. You can download from the B&S site the parts list, all you need to enter is model/type.
If youi wind up getting a new one, make sure it's installed right side up and have the proper air gap between it and the fly wheel.
good luck.


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## BillM2 (Oct 14, 2007)

*Got spark, sort of*

Update: I disconnected the black wire (shut off wire) that goes to the magnetron in front of the flywheel and here what happens: I am getting spark to the spark plug wire but not to the plug. But, when I wrap a wire around the base of the spark plug and ground it, I then get a spark to the plug (nice blue spark at the gap). Previously, when the black wire was connected to the magnetron, nothing. What's the problem?

Also what is the gap between the magnetron and the flywheel? Right now I have it eyballed away enough to clear without rubbing. Could an inaccurate gap be the culprit? I noticed that there are two wires (black and red) that go underneath the flywheel to a diode I believe, fyi.

I have a Briggs 12Hp engine (model 28407; type 1026-E1; code 980205ZA) on a Sears Craftsman Lawn Tractor (Model 917254520).


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## glenjudy (Aug 26, 2006)

Sounds like maybe the kill wire has a bare place on it and it is grounding out the coil. Remove wire completely and check for a bare place.
A gap of .010 will work fine.
hope this helps.
thanks


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## pyro_maniac69 (Aug 12, 2007)

or there is a safety switch not engagin the way its supposed to be


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## glenjudy (Aug 26, 2006)

Coincidentally, I'm working on a Briggs 18.5 twin right now with pretty much the same symptoms, i.e., with plug removed and grounded, there is spark, but, installed with spark plug tester, there's no spark and, the engine won't fire. I made sure flywheel key was good. 
I scoured the Briggs site for these symptoms and found a troubleshooting piece on the coil that stated if coil is getting weak it will spark when removed and grounded but not if installed, due to compression.
I don't understand this phenomona, but, installed a spare coil I had and engine fired right up.
go figure...


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## BillM2 (Oct 14, 2007)

*No Spark (continued)*

I ordered new safety switches (3 of them: seat, blade and clutch) and will report back on what happens once they're replaced.

The other possibility I have learned is that there could be a short in the wiring. 

If anyone knows how to by pass all the safety switches so I can get a spark to the plug (I've got spark to the spark plug wire), please let me know.


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## pyro_maniac69 (Aug 12, 2007)

take the shutoff wire off the coil, thats how you bypass all the safetys quickly, if you wanna pass them one by one to see which one it is, your gonna have to make a jumper wire


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## glenjudy (Aug 26, 2006)

Anxious to hear if this solves problem.


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## 30yearTech (Sep 14, 2006)

BillM2 said:


> If anyone knows how to by pass all the safety switches so I can get a spark to the plug (I've got spark to the spark plug wire), please let me know.


How do you know your getting spark to the spark plug wire?

There is no switch that prevents the current from going to the spark plug from the spark plug lead, so if your getting spark to the plug wire but you can't get it to jump the gap on the plug, then it's possible you have a weak coil, faulty plug connector or spark plug.


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## JerryinWI (Oct 25, 2007)

Check the tractor itself. It could be one of the safety cutoffs switches...seat...mower deck...reverse...low oil. Did you check your oil?

99% of the time it isn't the motor, it is the unit it powers. Engines are basically dumb, that is they only worry about is gas, oil and air. As long as they have that they'll run. The safety features the equipment has installed is generally the cause of the problem.


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## 30yearTech (Sep 14, 2006)

JerryinWI said:


> Engines are basically dumb, that is they only worry about is gas, oil and air. As long as they have that they'll run.


Well they might be dumb, but I bet they also worry a little about compression and ignition, that is of course if they are gonna start and run!


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## glenjudy (Aug 26, 2006)

*BillM2 - Some basics*

When you sit on the seat, have the clutch/brake locked down, and blades disengaged, does the starter turn the engine when you turn the key ??????
Do you have a good sparkplug installed ?????
Have you ever inspected the kill wire connected to the coil for a bare place or, ever tried starting engine with kill wire removed ????
Let us know so we can better help.
Thanks,


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## BillM2 (Oct 14, 2007)

So far I have replaced the solenoid, the starter and two switches (blade and clutch). I have a jumper wire on the seat switch because I was sent the wrong switch. I am only getting spark to the gap at the plug when I have grounded the plug (wrap a wire around the base and then ground). The spark I get isn't terribly bright. I have checked all my grounds and they all seem to be fine. I do not have the lights wired up as I have the hood off - could this be a cause...?

So, no spark to the gap of the plug only when I wrap and ground it. Any thoughts. Should I replace the magnetron too? The solenoid I got from local auto shop and looks pretty much as the old one -- two terminals and one smaller one.


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## 30yearTech (Sep 14, 2006)

*No the lights will not affect the ignition system!*

Bill,
First off, the ignition system on your engine is totally independent of any other electrical components on your mower(or engine for that matter). That is, it does not require a good battery, solenoid or starter motor to create ignition spark. 

That said, these items in good operating condition are required to spin the engine over for it to start, unless you also have a recoil starter.

The spark plug MUST be grounded to the engine block for spark to jump the gap. If you are getting spark to the plug when grounded, then it's working. If you cannot get the engine started there may be other issues.


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## BillM2 (Oct 14, 2007)

OK, here's what happens. I turn the ignition, the starter turns, the flywheel turns but I am getting no spark to the plug at the gap. When I disconnect the black safgety wire connected to the magnetron, I have spark through the wire to the plug, but not to the gap. Then, when I pull the plug, wrap the spark plug base in wire and ground that wire, I get a slight spark at the gap -- the clutch, blade and seat safety switches are engaged during this test.

I have replaced the two switches (blade and clutch) and am using a jump wire at the seat switch until I get the proper seat switch. 

I've checked all the ground wires and all appear to be fine. 

Could this be the magnetron or another component. 

Thanks for your input!


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## glenjudy (Aug 26, 2006)

Have you tried using starting fluid in the carb just prior to turning key?
I still suspect what I outlined in my 3rd post in this thread? You need a new coil.
Good luck.


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## 30yearTech (Sep 14, 2006)

BillM2 said:


> OK, here's what happens. I turn the ignition, the starter turns, the flywheel turns but I am getting no spark to the plug at the gap. When I disconnect the black safgety wire connected to the magnetron, I have spark through the wire to the plug, but not to the gap. Then, when I pull the plug, wrap the spark plug base in wire and ground that wire, I get a slight spark at the gap -- the clutch, blade and seat safety switches are engaged during this test.
> 
> I have replaced the two switches (blade and clutch) and am using a jump wire at the seat switch until I get the proper seat switch.
> 
> ...


Once again, the spark plug MUST be grounded in order for spark to jump the gap, if you have the plug attached to the lead wire and just hanging in the air it will never spark. If you are getting spark to the plug when you have the little black wire unplugged then the magnetron is working. The black wire you are unplugging in order to get spark is the kill switch lead, if you get no spark with this wire plugged in then there may be a problem with one of the safety interlock switches, the ignition switch or the kill switch lead wire. Jumping the seat switch may not work as many models incorporate a presence switch in the connector, that will ground out the ignition if the seat switch is unplugged.

It is possible as glenjudy explained that you may have a bad coil that is not producing enough voltage for the spark to jump the gap when the spark plug is installed in the engine and under compression. It is impossible to look at the spark from the spark plug and determine if it's good enough or not. You could use a spark tester that has a large air gap and if your coil produces enough voltage for the spark to jump the gap of the tester, then it is most likely good enough to run your engine.


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## BillM2 (Oct 14, 2007)

*No spark*

I think I'll wait for the correct seat safety switch to arrive and will replace the magnetron or magneto/coil and see what happens as Glenjudy recommends. Maybe there's not enough spark being generated to reach the gap. We'll see what happens.

I've tried staring fluid but no difference. All my grounds look good with no corrosion.

:dude:


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