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Simplicity Benn
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1,574 Posts
Discussion Starter · #1 ·
i have a 16 horse cast iron briggs in my '74 mtd 990 and am not getting any spark out of it. i know that 9 times out of 10 its not the coil that goes bad so right now im focusing on the other stuff. all the connections are tight. looks like someone changed the points and condenser recently. but im not sure if they did it right. with the battery in the tractor i took a wire from the positive terminal and touched it to the wire comming from the points, that gave me a dead short, telling me that the points/condensor are grounding out on something (probably the engine block) and killing my spark. i performed this test with the points in the closed position. i tried this same test with a test light and got the same result, a short. does this diagnostic make any sense to you guys? does it sound like the PO didn't install them correctly or is there something else causing this? the points are very clean and are set at 20 thou which is what briggs calls for. im ready to just screw the points and buy an electronic coil but wanna see if i can do anything with what i have before i go spending any money. any help here would be awesome! :thanku::thanku:

heres a picture of the beast.
 

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The Magnificent
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20,952 Posts
Junk it and send it to VA Benn. I'll take it off your hands, no charge.

Anyway, you're making sure the points are opening and closing correctly? That they are seated correctly?

Now let's look at the wires coming under the point cover. Move the kill wire out of the way and forget about it for now. The wire coming from the coil probably has the insulation rubbed off doesn't it? Leave the point cover off for now and and make sure it is properly connected to the points (as is the condensor wire). Make sure it isn't touching a darn thing else (look where it goes under the shroud too).

These things don't make a whale of a spark so it's hard to see. The spark plug must be completely immaculate or you won't likely see a spark. You can use a screwdriver to bridge between the spark plug tower and the head of the engine to check.

What about mouse damage? Any meesers building nests inside the shroud? Likely they chewed through the wire coming from the coil.
 

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Simplicity Benn
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1,574 Posts
Discussion Starter · #3 ·
Junk it and send it to VA Benn. I'll take it off your hands, no charge.

Anyway, you're making sure the points are opening and closing correctly? That they are seated correctly?

Now let's look at the wires coming under the point cover. Move the kill wire out of the way and forget about it for now. The wire coming from the coil probably has the insulation rubbed off doesn't it? Leave the point cover off for now and and make sure it is properly connected to the points (as is the condensor wire). Make sure it isn't touching a darn thing else (look where it goes under the shroud too).

These things don't make a whale of a spark so it's hard to see. The spark plug must be completely immaculate or you won't likely see a spark. You can use a screwdriver to bridge between the spark plug tower and the head of the engine to check.

What about mouse damage? Any meesers building nests inside the shroud? Likely they chewed through the wire coming from the coil.
yep, i've had it torn apart since monday evening. there was a mouse nest under the shroud like i had thought and they had chewed through the wire connecting to the points. i went out already and got another used coil thats in good shape. the briggs i have on ol' allis is identical to this one which also uses points and its very easy to see the spark on it, even with a dirty plug. i'll take a few pictures tonight so ya'll can get a better look at what's going on with this thing. i just wanna here it run!!:crybaby:
 

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Administrator
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12,687 Posts
Benn , gonna move this over to the MTD Forum , probably get some more hits over there. Lots of 990 fans on this site.
 

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1,247 Posts
First thing I would do is file the points. . .
 

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Banned
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2 Posts
check to see if the little plastic plunger is worn ..Sometimes they will ware down and it wont open the points ..good luck man let us know what you find
 

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Premium Member
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5,747 Posts
Based on one of the things you did in your original post, you may have fried the coil when you introduced 12V to it. That is why I asked the question about whether it was battery or magneto ignition. The best thing for you to do is find a later flywheel and the Magnetron coil. Failing that, you could replace the coil and keep it away from any 12V source. If you can convert to the Magnetron, your ignition system will be virtually bulletproof.
 

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Simplicity Benn
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1,574 Posts
Discussion Starter · #10 ·
I didn't think you had to replace the fly wheel when switching to a magnatron type coil. I switched out the coil on an old Briggs 3.5 hp tiller and it was just a straight swap, all I had to do was hook up the kill switch wire.

When I preformed the 12v test the coil wasn't hooked up to it. I simply had a wire comming from the positive on the battery to the primary wire comming from the points/condenser. I did this test with the points in the closed position and got a dead short. This tells something is grounding when it shouldn't be, correct?
 

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Simplicity Benn
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1,574 Posts
Discussion Starter · #11 ·
update: we have spark!! i went to C-tire to see about getting a new points/condenser, turned out i can get a magnetron kit to change my old points style coil into a magnatron coil and for less $$. its briggs part number 394970. a bit of a pita to install but i got in and am getting a nice bright blue spark!

heres a picture of what the kit looks like.
 

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Senior MTF Poster
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Very much surprised that conversion kit worked with your current flywheel as mentioned above.

"I switched out the coil on an old Briggs 3.5 hp tiller and it was just a straight swap,"

Ben, we are talking a different animal here, generally old cast iron B&S engines had different polarity in flywheel magnets.

Walt Conner
 

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Premium Member
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Walt is correct, the Magnetron kit should not have worked with the engine's original flywheel. Perhaps we don't know the history of this engine's ignition system. Years ago, I had one of these on a log splitter that I wanted to convert to Magnetron, B&S would re-polarize the flywheel for free if you paid the shipping, which was a lot cheaper than a new flywheel.
 

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Simplicity Benn
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1,574 Posts
Discussion Starter · #14 ·
started it up with out any issues! it does idle a bit to high, but thats nothing. the PO had the carb rebuilt but it wasn't installed until i got ahold of it. she runs great regardless! i love the deep engine sound of this thing. i took it for a spin and musta had the whole neibhor hood watching me! needless to say im thrilled with my 990!! cant wait to work it! the hydraulics seem to work well too. i gotta change/or top up the trans fluid on it, its within opperating range but is a bit lower then what i'd like it to be at.
 

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I bought this kit and the directions are for many engines, the part is the same as the one that's in the instructions, that's good. The spark plug wire comes out in a location not shown in the parts install paperwork.

The body of the module hangs down too far, and the catch doesn't catch on anything.

Had the flywheel re-polarized by B&S, six days round trip. But this kit isn't going to work. Should have bought a new coil and points. Will my re-polarized flywheel work with the standard points set up? I sent a copy of the above link along with it to Briggs, so have a need to know if re-polarizing means "recharging" or a "polar shifting?

Any clues?

Thanks
 
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