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Yesterday, I was mowing when I ran out of gas. So I refilled the tank and tried starting it. (Briggs opposed twin 19.5hp) It wouldn't start. So I got the starter fluid out, and that didn't work. So, I pulled the plug, placed it on the edge of the exhaust and noticed it wasn't sparking. So I let it set for an hour or so, and tried it again. If fired right up and did fine until I got to a bumpy part of the yard. I noticed it was trying to quit on me. With every bump, it would stall just a little. Until finally it stopped and wouldn't start again. And like before, no spark.

So, I put on another magneto, and that didn't solve the problem either. I disconnected the kill wire, and still no spark. I've got it on right side up. I've got it gapped just right (new business card).. So, I don't know what the hecks going on.

BTW, I placed the wrench on the magnets, and they seem to be good. My wrench stuck to it as normal...

With the kill switch detached, seems the ONLY thing that it could be would be both magneto's are bad. But considering that they're both new (within a couple of months and only a few hours on the one I removed) I'd say the chances of them being bad are very slim. Is there anything else? Something I'm missing? I've had this problem before, but that was because I'd installed the magneto upside down.

Multiple module failures within a short period of time, raises the possibility that you are getting battery voltage to the module, at least intermittently, which could mean a short in the wiring, possible key switch problem that is being caused by vibration and bouncing.

Look at the side of the module where the ground wire attaches, and see if the epoxy is cracked, and you even be able to pick up a burnt wire smell if you put your nose close to it.

ILENGINE said:

Multiple module failures within a short period of time, raises the possibility that you are getting battery voltage to the module, at least intermittently, which could mean a short in the wiring, possible key switch problem that is being caused by vibration and bouncing.

Look at the side of the module where the ground wire attaches, and see if the epoxy is cracked, and you even be able to pick up a burnt wire smell if you put your nose close to it.

Click to expand...

Nothing that even looks different that when I first bought the magneto's. No smell of burnt wiring. Tested the continuity of both mags. They were OK. So, if it's grounding out, it has to be from under the fly wheel. Because with the kill wire disconnected, then (minus a short from under the flywheel) the magneto, magnets & flywheel are completely separate from anything having to do with the key switch and other wiring to things like the safety switches... Right?

Or am I missing something.

Any tips of taking the flywheel off? The puller doesn't seem to be strong enough. I'm scared I'm going to strip out the small bolt holes.. It's really that tight. I don't have an impact or air tools. And I don't want to go banging on it. I puts some spray lube around the crankshaft end. Maybe it'll break loose.

I think if bat current has reached the coil the transistors are toast. Continuity check may not be enough. I have removed my Intek flyweel twice using the two threaded holes and a 2 jaw craftsman puller. I put some preload into the puller and tapped GENTLY with a soft hammer. It should POW off. The nut is at 100 ft lbs. There was a warning by Senior recently that prying on one edge relieves the pressure on the crank thrust bearings seen when using a hammer. I had no problem. The "class" (tightness) fit of the two screws will lend confidence. Screw them in all the way in.


Edit. I have not read here about using a little heat, so I guess most are successful with cold removal. Heat is risky and I would not attempt it without a heat probe or infra red thermometer. Maybe 175F max and circular motion only around the shaft with puller preload applied.

motoman said:

I think if bat current has reached the coil the transistors are toast. Continuity check may not be enough. I have removed my Intek flyweel twice using the two threaded holes and a 2 jaw craftsman puller. I put some preload into the puller and tapped GENTLY with a soft hammer. It should POW off. The nut is at 100 ft lbs. There was a warning by Senior recently that prying on one edge relieves the pressure on the crank thrust bearings seen when using a hammer. I had no problem. The "class" (tightness) fit of the two screws will lend confidence. Screw them in all the way in.


Edit. I have not read here about using a little heat, so I guess most are successful with cold removal. Heat is risky and I would not attempt it without a heat probe or infra red thermometer. Maybe 175F max and circular motion only around the shaft with puller preload applied.

Click to expand...

I bought a puller today. It didn't allow the two bolts to screw down far enough, so when I started cranking on the big bolt in the middle, the threads on one of the small bolts pulled out..... The only way to get the bolts in there far enough, is to take the center (pointed) cap off the big center bolt. If I did that, i'd be afraid that it would make the big center bolt unstable.

I don't think I'm missing anything. I got the big nut (and washer) off the end of crank (above the flywheel) that is the only that I know of that would hold it on. I guess it's just that darn stuck.

BTW, this forum needs a "thanks" button.

I have often modified pullers. If not too late (damaged thread), try this. Put a little blaster or other penetrate oil around the thread and tap gently with a soft (lead, brass, copper) hammer. Let sit 12 hours or over nite. Repeat for several days. The penetrating oil will work on the top of any corrosion and each soft strike breaks into a new layer of corrosion. Ideally , this is done with a little preload on the puller and tightened just a little (one hex flat) each day. If you have the capability drill and re-tap the stripped hole to next size up. Use an alignment jig to drill and tap so the new bolt will seat fully. A trick that sometimes works on the puller end. Cut and grind it to the desired length. At the grinder point the end by rotating the screw at a slight angle. Then use the big hex nut and maybe another drop in bushing to locate the puller tip. The nut is not screwed down . Leave an air gap for the flywheel to jump into.

hrdman2luv said:

I bought a puller today. It didn't allow the two bolts to screw down far enough, so when I started cranking on the big bolt in the middle, the threads on one of the small bolts pulled out..... The only way to get the bolts in there far enough, is to take the center (pointed) cap off the big center bolt. If I did that, i'd be afraid that it would make the big center bolt unstable.

I don't think I'm missing anything. I got the big nut (and washer) off the end of crank (above the flywheel) that is the only that I know of that would hold it on. I guess it's just that darn stuck.

BTW, this forum needs a "thanks" button.

Click to expand...

https://www.youtube.com/watch?v=KkaD3h8J6es

https://www.google.com/search?q=how....19539j0j8&sourceid=chrome&es_sm=122&ie=UTF-8 take a look at each of these videos & see if they help or not.

I should make a video of this, to show you exactly what I'm talking about... But I'll try explaining it first.

A standard test light (the one with the alligator clip on one end, and the sharp point at the other)... When I connect the clip to the negative post and the pointed end to the disconnected spark plug end (with the plug still screwed into the head) the engine cranks and runs (on the other cylinder that still has a plug wire connected)... When I pull the test light off of the plug wire, the engine shuts off.

I tested the ohms on the kill wire from the plug to the harness, and it's OK. The other end goes up into the key switch.

Also, when trying to crank the engine, with the test light connected to the negative side of the battery, and then touching the magneto, it fires off once. Once it fires off, it continues to turn over, but no spark to the plug.

While turning the engine over, and a test light stuck into the kill wire, the light doesn't come on.

It's almost like the plugs aren't grounded.

FAQ | Lawn Mower Safety Tips | Briggs & Stratton Read through this and see if it helps, let us know how it goes.

You can also email Thomas Eidson CRC Tech with B&S with your engine problem: eidson.thomas@basco.com
If you decide to email, send engine numbers: model xxxxxx, type xxxx, trim xx.

ILENGINE said:

Multiple module failures within a short period of time, raises the possibility that you are getting battery voltage to the module, at least intermittently, which could mean a short in the wiring, possible key switch problem that is being caused by vibration and bouncing.

Look at the side of the module where the ground wire attaches, and see if the epoxy is cracked, and you even be able to pick up a burnt wire smell if you put your nose close to it.

Click to expand...

I think you're onto something about the key switch. That's about the only other source of electricity that could be getting the kill switch. Except when you consider that I don't get any spark when the kill switch isn't connected either...

BTW, it started yesterday for about 2 stokes. Most of the time, it fires for one stroke. But that's it. It take a few minutes for it to do it again just like that.

Inside the Magnatron ignition module (yours is a diff model than my Intek which uses Magnatron) are two transistors . You seem to be applying 12V sometimes. The transistors run on 5 micro amps (5 one millionths of an amp?). If you have applied bat voltage the little transistors are ruined and no amount of continuity check or probing will bring them back. It is characteristic of a a failed transistor to sometimes work, but not continuously. I have never seen any Briggs discussion of the guts of the module, probably because it's Greek to many on the forums. These modules are probably encapsulated (potted- after the circuit is soldered up it is placed in a mold and a special casting resin is poured in, then cured.) The modules live bolted on to the iron of the engine which is normally a "heat sink," which draws heat away from the transistors who only tolerate up to 250F (probably less). Vibration is also the enemy. It appears the pros know well how many ignition modules are ruined with the best intentions gone wrong. These modules are rugged while also being fragile (to stray excess voltage). Well again I am on my soap box, and before you can pelt me with garbage I sign off. Your humble servant.:laughing:

motoman said:

Inside the Magnatron ignition module (yours is a diff model than my Intek which uses Magnatron) are two transistors . You seem to be applying 12V sometimes. The transistors run on 5 micro amps (5 one millionths of an amp?). If you have applied bat voltage the little transistors are ruined and no amount of continuity check or probing will bring them back. It is characteristic of a a failed transistor to sometimes work, but not continuously. I have never seen any Briggs discussion of the guts of the module, probably because it's Greek to many on the forums. These modules are probably encapsulated (potted- after the circuit is soldered up it is placed in a mold and a special casting resin is poured in, then cured.) The modules live bolted on to the iron of the engine which is normally a "heat sink," which draws heat away from the transistors who only tolerate up to 250F (probably less). Vibration is also the enemy. It appears the pros know well how many ignition modules are ruined with the best intentions gone wrong. These modules are rugged while also being fragile (to stray excess voltage). Well again I am on my soap box, and before you can pelt me with garbage I sign off. Your humble servant.:laughing:

Click to expand...

Most of what you just said, is completely greek to me. But, I think I understand at least some of it.

First question, if what you said applies to my magneto, would the magneto still work when I connect the test light ground (on the negative side of the battery) to the end of the plug wire? When I do that, the cylinder that still has a plug & plug wire connected is firing right. When I switch them (connecting the test light to the other plug) then the other cylinder runs fine. The engine will crank and run off of one cylinder, as long as I have that test light connected to one disconnected plug wire (disconnected from the plug)

Sorry if I didn't explain that right. I think I did. But long day at work, and my sleeping pill is kicking in..

hardman to stop: Like your persistence so more blather from me. The battery is negative ground, right. That means touching the negative terminal is simply 0 volts. You also get that 0 volts anywhere on the metal frame or engine. So (If I'm reading you properly) you are grounding the spark lead . But if you accidentally put POSITIVE battery contact to the module(12V) you have instantaneously destroyed the transistors-no going back. Are we understanding the cylinder firing moves with the one module only? Remember that the failed transisors may put out an occasional spark, but be inoperative. Shaky here, but if your machine is like mine one module's behavior will not affect the other's. These magneto systems are not like auto systems and generate their own voltage without the battery . The really small time it takes to destroy a transistor would not heat up the resin body so you could smell it (like a burning electric motor or failing truck brakes on a downhill). We feel your pain and await a breakthru.

motoman said:

Inside the Magnatron ignition module (yours is a diff model than my Intek which uses Magnatron) are two transistors . You seem to be applying 12V sometimes. The transistors run on 5 micro amps (5 one millionths of an amp?). If you have applied bat voltage the little transistors are ruined and no amount of continuity check or probing will bring them back. It is characteristic of a a failed transistor to sometimes work, but not continuously. I have never seen any Briggs discussion of the guts of the module, probably because it's Greek to many on the forums. These modules are probably encapsulated (potted- after the circuit is soldered up it is placed in a mold and a special casting resin is poured in, then cured.) The modules live bolted on to the iron of the engine which is normally a "heat sink," which draws heat away from the transistors who only tolerate up to 250F (probably less). Vibration is also the enemy. It appears the pros know well how many ignition modules are ruined with the best intentions gone wrong. These modules are rugged while also being fragile (to stray excess voltage). Well again I am on my soap box, and before you can pelt me with garbage I sign off. Your humble servant.:laughing:

Click to expand...

I would love for Briggs and Stratton to come out with a test for the solid state part of the magnetroin. My problem you buy a new one and there is no way to know if it is good, You shuold be able to test the resistance in a transitor safely if you observe the correct polarity

hnstr, It is frustrating to live in the digital age because just below the surface of the buttons is a very complex world few care to understand. If this forum stimulates even a few to pursue further study of e.g., transistors , this will be very good. But they cannot be understood with street sense. Far from an expert I did study this stuff many years ago. Ideas like "resistance" are really quite different when you study transistors. An education is available online , but probably somewhat frustrating. So the ignition module for most will be understood in this forum as simply "good" or "bad." Probably the best bet is to try to buy top line replacement which "should" have reliable parts inside and then do not overheat or allow stray voltage near them. Have a good holiday. motoman

motoman said:

hnstr, It is frustrating to live in the digital age because just below the surface of the buttons is a very complex world few care to understand. If this forum stimulates even a few to pursue further study of e.g., transistors , this will be very good. But they cannot be understood with street sense. Far from an expert I did study this stuff many years ago. Ideas like "resistance" are really quite different when you study transistors. An education is available online , but probably somewhat frustrating. So the ignition module for most will be understood in this forum as simply "good" or "bad." Probably the best bet is to try to buy top line replacement which "should" have reliable parts inside and then do not overheat or allow stray voltage near them. Have a good holiday. motoman

Click to expand...

Thanks you for that..

I put on the other magneto, checked the kill wire after it started up, and no voltage was coming through it... After about 30 minutes, it stopped and now no spark through the plug wires.. I'm thinking seriously about rewiring it without the safety switches. And "extra's"... I don't know. I might just put it away until next spring.. Luckily for me, I've got another one that works great....

Happy Thanksgiving to you and yours.. And everyone else on this forum.