12V battery ignition with/Automotive coil conversion on 1-Cyl Cast Iron Briggs

1489 Views 24 Replies 8 Participants Last post by dekrise81, 13 d ago

Charlottedarter

Discussion Starter · Feb 7, 2022

Hey guys, I finally got around to working on this old Briggs and Stratton engine, Montgomery Ward Variable Speed 15 that I picked up as a donor tractor for my Gilson, needed a transaxle. Posting here as the issue is the B&S that is common to lots of older garden tractors.

Well, I found another Peerless 2300 series transaxle and decided to get this old thing working. I started to work through the engine to get it working, no spark a few years ago when I picked it up. It turned over by key, but no spark, so it just sat in the back yard, as with no trans, it was of no use but for parts. It has a Briggs and Stratton Single Cyl cast iron engine, I'm guessing 15 hp, Anyway, looks like the original coil bit the dust, and the previous owner cut the wires and installed an automotive coil and switched to 12volt ignition from magneto to prevent having to pull the engine to replace the old coil. New system for me to work on, so after lots of "learnin" on the subject via forums and Youtube, everything tested out as good, or appeared to, and with some adjusting at the points, it finally fires a strong spark. While testing, I left the points/condenser cover off the engine, and while there is a small spark at the points when turning over, there is a big nasty spark as soon as I stop turning over. I haven't put gas in it, still need to clean the carb, but considering the way these Flo-Jet carbs tend to leak, that spark has me concerned. Is that normal? Likely to cause any problem? Once the cover is on, it isn't likely to be a problem with the gas if it leaks, just curious on what I should expect going forward. Thoughts?
Considering white powdery dust came out of the hole when I pulled the high speed needle valve out of the carb bowl....carb will need a thorough cleaning, possible re-built parts, before this thing will run.

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Bruce Dorsi

· #2 · Feb 8, 2022

You didn't say how you are controlling the ignition power.

If the "nasty spark" is occurring after the switch is turned off (battery power disconnected), the spark may possibly be the ignition coil discharging.

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Charlottedarter

Discussion Starter · #3 · Feb 8, 2022

The condenser is attached to the neg post of the coil, same as the points, so when 12v power is disconnected via the key switch, the condenser should pick up any excess charge, then dissipate it through its case ground. Or at least that is how I understood the instructions on this set up. In testing, the condenser would take a charge from the Ohm meter, and when switching to volt meter, you could see the charge dissipating. Looks to be brand new condenser and points...likely the point of past failure, previous owner probably replaced them and never got it running. The points were closed tightly when I got it. Anything else I should be looking for? Is it likely the points and/or condenser will fail in short order?

I was able to run the tractor today. I'd bet it was the first time it ran in at least a decade...maybe two.
I went into cleaning up the carb, and realized I would need a rebuild kit for it. Needle valve at the emulsion tube was all grooved up, gasket got torn up pretty good. Really crudded up inside. Just wasn't going to make it work today. I found a complete spare carb in my parts bin, and it looked like it was in good shape. Needle valve was perfect. I sprayed some carb cleaner through the jet, it appeared to atomize nicely. Installed it, clean gas, and fired it up. Started immediately, minor adjustment on the carb at the needle valve, and it ran nicely. I need to do some work on my throttle linkages and get it to idle down. In fact, I have a few things to do before it is drivable. Install brake friction material, make a brake lock lever, purchase and install a better muffler, and get a battery. I was using a battery from another tractor and the tray on this tractor was rusted out, didn't hold the battery well, and the exposed belt rubbed on it, eroded a hole in the plastic case of the battery, so now I need two batteries, and a means of securing the new one. Need to come up with a seat for it too.

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Achto

· #4 · Feb 8, 2022 (Edited)

This is entirely up to you but this is what I do with the ignition on a cast iron Briggs. Purchase a Briggs #398811 coil or aftermarket equivalent. This part number will fit most Briggs from 7hp to 16hp.

Install the coil backwards, there will be makings indicating cylinder side or some thing similar. You would want the cylinder side facing out away from the cylinder. Reason for this is that the polarity on the fly wheel magnet is reversed on a cast iron Briggs as compared to the newer aluminum Briggs engines. Cut the wire that goes to your points but leave the points installed to plug the hole. Run a kill wire from the new coil to a switch that will ground the coil to kill the engine. You now will have a solid state coil with no points to worry about. I install a solid state coil on every Briggs that I own, specially if they have the points under the fly wheel.

Your battery ignition that you have now will work just fine with out issue. If nothing else the above info may help you on a future project.

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Charlottedarter

Discussion Starter · #5 · Feb 8, 2022

Thanks Achto, that is really all I wanted to know, that it will work fine as it is.

Getting access to the coil is the problem, which is why the previous owner installed the automotive coil and just cut the wires from the old coil. The drive line comes off the crankshaft as a drive shaft connected at the flywheel side. Not easy to get the tins off.
Haven't decided if I will tear it down and restore it, or just clean it up and use or sell it. If I restore it, I will probably go your route with the solid state coil and eliminate the points. I am familiar with the process you outlined above. Briggs used to swap polarity on flywheels for free, well, you would have to pay shipping both ways for them to do it. Why would they not just tell people to install the coil backward as you indicated...Not sure why anyone would go through the effort of mailing the flywheel.
Thanks for the responses.

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29 Chev

· #6 · Feb 8, 2022

Some automotive ignition coils for use in 12 volt systems are designed with a resistor built into the primary winding to limit current and some are designed to be used with an external ballast resistor. If a coil that is designed to be used with an external resistor is fed 12 volts without a current limiting device (some automotive applications use a special resistance wire rather than an actual resistor) the coil will probably fail in a short time period due to overheating. This information may be something that you (and the previous owner who installed the coil) may or may not be aware of.

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Achto

· #7 · Feb 8, 2022

29 Chev said:
This information may be something that you (and the previous owner who installed the coil) may or may not be aware of.

Good point. Definitely need to make sure that you have a coil with an internal resistor. This info should be printed on the coil

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Achto

· #8 · Feb 8, 2022

Charlottedarter said:
Briggs used to swap polarity on flywheels for free, well, you would have to pay shipping both ways for them to do it.

One other under lying issue. If BS found any defect in the fly wheel that you sent in, they would scrap it and you would be out one fly wheel.

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Charlottedarter

Discussion Starter · #9 · Feb 8, 2022

I am aware of the need for a resistor...haven't removed this coil yet to inspect, but there is no info on the forward facing bits. Working today and tomorrow. Might get a chance to pull it apart later this evening.

On the flywheel, something as small as a chipped fin would forfeit the part. Nothing about that whole thing made any sense.

Everyone ought to get a kick out of this one..."I wonder if Flex Seal would patch up the battery?" For Chits and Giggles, I might just give it a shot. It is just a tiny hole. I put it in a plastic bucket last night, and there are only a few drips in the bucket. Damn thing is an $100 battery. That is a lot for a tractor that I have no specific use for. Working on charging a smaller lawn tractor battery to see if it is enough to make this thing fire, and if so, that will be the route I go.

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Charlottedarter

Discussion Starter · #10 · Feb 9, 2022

Another minor issue on this engine, what holds the throttle cable in the metal clip? The linkage arm that extends from the governor arm to the top of the engine connects to the cable, but the sheath for the cable protrudes through two consecutive holes on a sheet metal type clip. Nothing there to hold the clip, no way to install a nut. Cable sheath just slides up and down in the clip. Not smoothly of course, but it isn't fixed and stable. Do they sell a clip for it? Anyone have a part number?

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MNGB

· #11 · Feb 9, 2022

There are special nuts that screw on to the cable case to lock it in place and there was also a U shaped clip that slipped over the cable casing and the mt on the engine. I have used SS lock wire wrapped 2-3 times around the cable up or down over the mt and then 2-3 wrapes again then tie the 2 ends together

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MNGB

· #12 · Feb 9, 2022 (Edited)

This is the nut that screws on to the cable casting to attach and adjust the throttle cable 2 required FYI the OEM cable is needed the new replacements from China are metric and will not work

Briggs & Stratton :: 63426 Briggs and Stratton Throttle wire stop nut 691027 Fits many Antique B&S engines

Genuine B&S throttle wire nut threads onto your throttle wire to set control length on the cable If you have any questions let us know

bolenspartsandsupplies.com

bolenspartsandsupplies.com

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dekrise81

· #13 · 21 d ago

Achto said:
This is entirely up to you but this is what I do with the ignition on a cast iron Briggs. Purchase a Briggs #398811 coil or aftermarket equivalent. This part number will fit most Briggs from 7hp to 16hp. Install the coil backwards, there will be makings indicating cylinder side or some thing similar. You would want the cylinder side facing out away from the cylinder. Reason for this is that the polarity on the fly wheel magnet is reversed on a cast iron Briggs as compared to the newer aluminum Briggs engines. Cut the wire that goes to your points but leave the points installed to plug the hole. Run a kill wire from the new coil to a switch that will ground the coil to kill the engine. You now will have a solid state coil with no points to worry about. I install a solid state coil on every Briggs that I own, specially if they have the points under the fly wheel. Your battery ignition that you have now will work just fine with out issue. If nothing else the above info may help you on a future project.

I am new to this type of thing. I am a mechanic or was. What is the blade connector on the new coil for? Where do you put the kill wire on the coil? I bought an MTD 990 with a 16hp Briggs that stopped running for the previous owner. The engine spins freely just needs spark.

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Achto

· #14 · 21 d ago

dekrise81 said:
What is the blade connector on the new coil for? Where do you put the kill wire on the coil?

The blade connector is for the kill wire.

Welcome to GT Talk.

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dekrise81

· #15 · 20 d ago

Achto said:
The blade connector is for the kill wire.

Welcome to GT Talk.

Thank you sir.

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Bud W

· #16 · 20 d ago

If the coil has the tab to kill spark, it is not battery ignition, it's a Magnetron coil (no points & condenser required). Be careful, the ignition switches are different between the two. Battery ignition switch supplies 12 volts to the ignition coil while the switch for the Magnetron ignition provides the ground to kill the spark. Using the wrong switch is not good.

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dekrise81

· #17 · 20 d ago

Thank you, so basically the ignition switch would be to break the ground and send power to the solenoid?

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MNGB

· #18 · 20 d ago

dekrise81 said:
Thank you, so basically the ignition switch would be to break the ground and send power to the solenoid?

No in a battery ignition system the ignition switch supplies 12 VDC to the coil and then on to the points, thru the "I" terminal on the ignition switch, the "S" terminal on the switch goes to the starter solenoid

Rectangle Font Schematic Parallel Slope

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MNGB

· #19 · 20 d ago

dekrise81 said:
Thank you, so basically the ignition switch would be to break the ground and send power to the solenoid?

No in a battery ignition system the ignition switch supplies 12 VDC to the coil and then on to the points, thru the "I" terminal on the ignition switch, the "S" terminal on the switch goes to the starter solenoid

Bud W said:
If the coil has the tab to kill spark, it is not battery ignition, it's a Magnetron coil (no points & condenser required). Be careful, the ignition switches are different between the two. Battery ignition switch supplies 12 volts to the ignition coil while the switch for the Magnetron ignition provides the ground to kill the spark. Using the wrong switch is not good.

Hi Bud you are right with the exception that the early 16 hp cast iron B&S does not use the magnetron system it had a regular B&S magneto later one can be converted to madnetron sytem

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dekrise81

· #20 · 16 d ago

I got the new coil/magnetron installed with the cylinder side facing out and we have ignition. Thanks for the information on that, I still need to wire a kill to it but now that i know she runs i am going to start cleaning and restoring. It needs a carb as well. But this is cool being new to this. It is a MTD 990 with a 16hp Briggs. Thanks again, i am sure i will need more help.

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