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Discussion Starter #1
I can't seem to get a good hot spark on my 16 hp Briggs on my 990. I replaced the old magneto with a new one. Set the air gap between 10-14 1000's like the book says. I think I may have some wiring problems. Can anyone talk me through the proper wiring of the magneto. My understanding is with a new magneto you no longer need to worry about the wire from the points. Is this correct? What about the wires that come with the new magneto. There are two wires with a spade connector. Where do they go? How about the magneto wire from the ignition switch. I'm really confused. Please help!!!
 

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MTD 990 Twactor Guy
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I just replaced the magneto on my 990. The wire connector to the back of the magneto, 1 to a ground on the motor - behind the carburetor, and the other just gets cut off, bent over and taped. Make just you use the "tag" provided with the magneto as a gap between it and the magnets on the flywheel.

Mine works great - good luck with yours!
Rich
 

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I have pretty weak spark with my magneto upgrade as well (engine model is 320420). I inquired for solutions in the small engines/repair forum but never got any reasonable answers. Also sent a message to Briggs' support and never got a response, come to think of it.

Regarding the wiring of the little black wire I never got mine quite right either. The basic principle is that when it touches ground it stops the spark, but for whatever reason (probably a bad ignition switch) I could only get it to work with my ignition switch right when I hooked it to the starter connector. In other words, I actually turn my key to the start position to shut down the engine :)

If you can supply a description of your switch (how many prongs and what markings there are on it) I could provide better help.
 

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Discussion Starter #4
I'm not sure of my engine #'s. I would have to check them again. My ignition switch has 5 male prongs that plug into the 5 female plugs on the wiring harness. The prongs are labeled as follows: M,B,L,S,G. I figure these to mean M=magneto, B=Battery, L=Load, S=Start and G=Ground. If you have a manual for the tractor there is a wiring schematic in it. I've tried to make sure that I've followed it. But I must have something wrong. If you need a copy let me know and I'll e-mail it to you. I have two other 990's and no problems. Good hot spark. One of them has some kind of little electronic module I've never seen and the other has the "M" wire connected to the wire that was removed from the points. I haven't checked the magneto wiring on these because I really didn't want to have to remove the hood, grill, engine shroud and flywheel to compare the wiring. I had hoped someone could help but if I can't get any answers then I guess I haven't much choice. I hope not!!!!!
 

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Weak flywheel magnet ???
I googled for "Magnetron weak spark" and the first result was my own post. OK, so that wasn't too helpful...

But I did see this on Briggs' site:

The flywheel magnet must generate a sufficient magnetic field to start the chain of events in motion. A fair test is to hold the flywheel on edge with the magnet facing up. Place the blade of a 10" #3 (1/4") straight blade screwdriver against the magnet. Release the screwdriver. The magnet should have enough strength to hold the screwdriver straight out. If we pass this test, assume the magnet is OK.
 

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Discussion Starter #7
I don't think it's a weak magnet because when I go to adjust the air gap on the magneto the magnet really pulls the magneto down with a lot of force. My dilemma is that I had the tractor running and was working on restoring it. When I went to start it again later it wouldn't start. Anymore suggestions?
 

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Discussion Starter #8
Thanks for that quote from the Briggs site. I'll give that a try and get back to you with the results. In the mean time if you should happen to come up with any other suggestions feel free to send them out. Thanks again
 

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The prongs are labeled as follows: M,B,L,S,G. I figure these to mean M=magneto, B=Battery, L=Load, S=Start and G=Ground.
L = Lights.

The kill wire should go to the M prong. Verify that there's continuity between the M prong and ground when the key is in the off position, and similarly verify that there is no continuity when it isn't.
 

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I had the same problem and got mine to run.

I started at the battery and when to the starter wire brushing everything until shinny and then put dielectric greese on the connections. Then I took the starter off to take a peek inside and it had a thick coating of brush material. So I took some electrical cleaner and sprayed everything down put it back together and gave it a shot of starting fluid in the carb as I had no gas in it and it fired almost instantly then ran for a few seconds until the fluid ran out and then died so i need to get some gas on the way home. I do need to get that starter redone as the bearings are a lil noisy and the plastic insulaters for the leads are not in good shape but it runs for now until i get it to someone that can repair it a lil better than I have. Perhaps your having the same problem.
 

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"The wire connector to the back of the magneto, 1 to a ground on the motor - behind the carburetor, and the other just gets cut off, bent over and taped."

Let's be clear about this. The wire connects to a junction to which the "kill" wire from the switch or safety switches attach, not a full time ground.

"The basic principle is that when it touches ground it stops the spark, "

Correct.

I think you will find that typically an engine equipped with points and condenser will have a hotter fire at lower rpm than the CDI (electronic ignition) You need to spin a CDI about 800 rpms to get a spark.

Walt Conner
 
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