Export thread

I have a craftsman rider (model 31p7770348e1). Recently my craftsman would not start and I was getting no spark. Diagnosed down to the magneto and replaced. The mower started once and then no spark. I disconnected the kill and still no spark. so... I replaced the magneto again. Onc again it started and ran but then would not restart. Same problem... I changed spark plug as well... What would kill two new magnetos? I don't want to kill another?

wetweasel said:

I have a craftsman rider (model 31p7770348e1). Recently my craftsman would not start and I was getting no spark. Diagnosed down to the magneto and replaced. The mower started once and then no spark. I disconnected the kill and still no spark. so... I replaced the magneto again. Onc again it started and ran but then would not restart. Same problem... I changed spark plug as well... What would kill two new magnetos? I don't want to kill another?

Click to expand...

Positive voltage to them.

reynoldston said:

Positive voltage to them.

Click to expand...

yep... thank you

reynoldston said:

Positive voltage to them.

Click to expand...

Please explain in detail. Because I'm having the same problem. I just bought my 3rd magneto.

hrdman2luv said:

Please explain in detail. Because I'm having the same problem. I just bought my 3rd magneto.

Click to expand...

I order for the coil to operate you want no type of voltage to the primary wire (small wire) positive or negative. Now to stop the engine from running you will need negative voltage to the primary wire. If at any time you do get positive voltage to the primary side you will cause a short in the coil and can burn it up.

Another thing is what are you using for coils. A good OEM coil or a aftermarket Chinese junk??

reynoldston said:

I order for the coil to operate you want no type of voltage to the primary wire (small wire) positive or negative. Now to stop the engine from running you will need negative voltage to the primary wire. If at any time you do get positive voltage to the primary side you will cause a short in the coil and can burn it up.

Click to expand...

So you're talking about getting voltage back up the kill wire to the magneto... What could cause this? It started and ran fine today (19.5 opposed twin briggs)
But after I killed it, it wouldn't get spark. While holding the plug against something grounded, it didn't spark most of the time. But when it did, it would spark a lot.

A couple of weeks ago, when this first started, it seemed to cut out when I hit bumps. That's when it died and wouldn't crank back up.

When it does crank & run, it cranks & runs greats. But, it's sporadic as to when it cranks & runs.

reynoldston said:

Another thing is what are you using for coils. A good OEM coil or a aftermarket Chinese junk??

Click to expand...

The first one was from a briggs dealer, Came in a briggs box. The next one I got from Ebay, was the same kind. (only a lot cheaper) I noticed it's different than the one I took off originally.

Hrs an, it sounds to me like you have a kill wire which is shorting out to ground. Check the entire length of the kill wire, looking for areas which are either pinched or rubbed bare.

Rivets said:

Hrs an, it sounds to me like you have a kill wire which is shorting out to ground. Check the entire length of the kill wire, looking for areas which are either pinched or rubbed bare.

Click to expand...

Even with then kill wire disconnected, many times I'm not getting spark to the plugs.

If you got the primary wire disconnected and the coil is installed right there is nothing else unless there is a ignition timing module.

reynoldston said:

If you got the primary wire disconnected and the coil is installed right there is nothing else unless there is a ignition timing module.

Click to expand...

Keep in mind, it acts like there's a short, because it cuts out real bad when I hit bumps.

You need to check all wiring," hands on", making sure everything is tight and secure, especially ground wires & straps. Also check for corrosion, rust, bare wires. Let us know what you find, thanks.

mechanic mark said:

You need to check all wiring," hands on", making sure everything is tight and secure, especially ground wires & straps. Also check for corrosion, rust, bare wires. Let us know what you find, thanks.

Click to expand...

I checked all the wires and safety switches. All seemed ok..

But, here's what I did find. I put a normal test light (clipped to the negative post on the battery) and stuck it into the plug wire. (The end of the plug wire disconnected from the plug)... The darn thing fired right up. The cylinder that was still connected to the plug ran like normal. When I disconnected the test light from the plug wire, it died.

So, only when grounding out the plug wire, does the magneto send fire to the plugs.

Where the magneto is mounted, is clean. I have a separate ground wire going from the block to the frame. (a pretty big one)

BTW, one thing I need to check... I didn't have the ground plug connected to the magneto when I was using the test light as the ground.

I just received a new coil. Debating on whether or not to put it on. Because I still get spark into the plugs, at certain times. Like when I connect the test light to the plug wire.

hrdman2luv said:

I just received a new coil. Debating on whether or not to put it on. Because I still get spark into the plugs, at certain times. Like when I connect the test light to the plug wire.

Click to expand...

You might just as well use the new coil you own it. Anyplace I ever did business with wouldn't take back any electrical parts.

reynoldston said:

You might just as well use the new coil you own it. Anyplace I ever did business with wouldn't take back any electrical parts.

Click to expand...

I guess I'm just scared that it's not the coil that's causing the problem. After all, when I ground one of the unplugged plug wires, the other one fires like crazy. And when I switch the ground wire to the other plug wire, and connect the first one, it fires like it's supposed to... And regularly, they'll both fire for a second or 2.

Check the magneto ground. Measure the resistance between the plug and ground. Shoild read about 7k ohms.
Check for voltage on the kill wire with it disconnected the the ignition on.Should read no voltage
Check the resistance of kill wire to ground. Should read infinity.
Check kill wire for loops. there should be no loops even one.
If all check out it should be safe to replace magneto

hntrsr said:

Check the magneto ground. Measure the resistance between the plug and ground. Shoild read about 7k ohms.
Check for voltage on the kill wire with it disconnected the the ignition on.Should read no voltage
Check the resistance of kill wire to ground. Should read infinity.
Check kill wire for loops. there should be no loops even one.
If all check out it should be safe to replace magneto

Click to expand...

Thanks for that... One more question (Because it's raining and can't get out there and do anything today) The end of the magnets (on the flywheel) aren't flush with the flywheel. They actually stick inward about 1/4". Should they be flush with the edge of the fly wheel? They don't appear to be chipped or broken. And my small wrench will stick to it pretty good..

Engine model number 42E707-2631-E3. On the diagram, from Parts direct, they don't list the magnet as an actual part. So I might have to buy (If needed) the whole flywheel... Over $200.. WOW

I would say the magnet is fine, as long as it isn't hitting anything. Each end of the secondary winding in that coil connects to a spark plug. What you are seeing indicates there is a problem with the secondary winding. Replaced the coil and make sure there isn't a short some place that is sending power to the ground plug on the coil.

had one a few years ago that would only fire with one wire disconnected.

I put the new magneto on today, and it ran fine. Like normal.. 3rd one in less than 10hrs of use. Weather permitting, I'm going to check a few things tomorrow. I know there was no electricity coming through the kill wire... Could it be two bad magneto's? Seems those things hardly ever go bad...

Maybe these "new and improved" parts aren't so improved... I noticed it wasn't the same as the one that came it when I got it. But Parts Direct says it's a correct substitute....

I don't think your magneto was bad from what you did It seems the ground to the magneto was missing.
When you connected the test light between the negative battery terminal and the plug wire you provided a ground
though the coil. Congrats and good luck

hntrsr said:

I don't think your magneto was bad from what you did It seems the ground to the magneto was missing.
When you connected the test light between the negative battery terminal and the plug wire you provided a ground
though the coil. Congrats and good luck

Click to expand...

I was thinking about putting a ground wire from the magneto to the frame, just to see. But didn't because when I touched the test light (grounded at the - battery post, it didn't work like when I stuck into the plug wire...

If this magneto goes, then I'll be back to step one... Once again.