Briggs & Stratton WI

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  #1  
Old 11-28-15, 12:13 PM
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Briggs & Stratton WI

Hi All, I am trying to restore a WI, problem I am having is I can't get a consistant spark,things I have tried :
New plug,new condenser,set gap on flywheel,set points and plug gaps,key way in flywheel seems tight ,magnets are clean ,using an inline spark tester the magneto seems to have consistant spark but when attached to the spark plug in the cylinder the spark is very intermittent .
Thoughts
Geo
 
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  #2  
Old 11-28-15, 12:43 PM
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You might be able to get a magneto for it that will eliminate the points.
Also what kind of plug are you using, and have you tried more than one?
 
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Old 11-28-15, 04:59 PM
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B & S has a Antique site on their website. Also there is a guy on u tube that repairs all those OLD engines i'll put a link up later ~!~!
 
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Old 11-28-15, 05:24 PM
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Shopdogsam is his channel I need to go visit him next summer ~!~!
 
  #5  
Old 11-28-15, 06:48 PM
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I really want to keep it as stock as possible,the original plug was in good shape, I did replace it with a J8 I think it was ,same as the orig.
 
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Old 11-28-15, 06:53 PM
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That would be great!!!!!!!!!!!!!!!!!
 
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Old 11-28-15, 11:39 PM
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Have you checked the points to be sure they are making good connection with an ohmmeter?
 
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Old 11-29-15, 05:13 AM
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No, but I will,thanks for the tip,is there a way to bench test a magneto?
Geo
 
  #9  
Old 11-29-15, 09:54 AM
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Points test closed even though they are open,what am I missing here ? I need a schematic of how this ignition systems works.
 
  #10  
Old 11-29-15, 10:48 AM
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Disconnect the wire going to the points and check for continuity to ground. If continuity is detected, find where the wire is shorted. Also make sure the insulator that the wire connects to is not missing broken or otherwise allowing continuity to ground.

Here is a basic generic diagram.
 
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Old 11-29-15, 10:52 AM
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I really want to keep it as stock as possible
What particular application or reasoning for this?
Replacing the magneto and points system, with an electronic magneto, will not in any way change the appearance and infact, the points can be left in tact.
 
  #12  
Old 11-29-15, 12:32 PM
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I just want to see if can get it to run with what is there,something to do in my spare time,may end up going to electronic in the future, any idea what module I would use,never did it before.
Thanks for the drawing
Geo
 
  #13  
Old 11-29-15, 12:39 PM
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Here is a link to a test for points and condenser, disregard the reference to outboard. Have a good one. Geo

http://assets.fluke.com/appnotes/ele...r/B0271b_u.pdf
 
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Old 11-29-15, 01:18 PM
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Have an older, breaker point ignition system?

Breaker point ignition systems were common through 1982. You can improve its reliability on a single-cylinder Briggs & Stratton engine equipped with breaker points and a two-leg armature by installing a solid-state ignition conversion kit (service part number 394970) that bypasses the points (conversion kit will not work with a three-legged ignition armature).
breaker point ignition system converter kit
How To Test & Fix Ignition System Problems | Briggs FAQ
 
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Old 11-29-15, 01:26 PM
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Disconnect the wire going to the points and check for continuity to ground. If continuity is detected, find where the wire is shorted.
I believe you would have a normal ground to that wire through the coil. There would be varying resistance depending on whether the coil was hot or cold. I never had any luck checking coil resistance since one that checked good still failed after it had been running.
 
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Old 11-29-15, 05:34 PM
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If you look at the diagram, which mind you is basic, the other side of the points, or where they mount to the engine is direct to ground. If the wire from the coil is shorted, or it's path is interrupted to the coil, then the circuit never opens when the points do which is what causes the collapsing field in the coil which provides the high voltage to the spark plug.

I do agree with testing coils, IIRC, ohm 8-20K, but not always conclusive. Much like the test for the John Deere igniter module, you have to find it in a failed state to confirm it bad or replace with a known good unit.
 
  #17  
Old 11-29-15, 07:23 PM
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If the circuit between the coil and points is shorted the system wouldn't work. But if you check the coil side of the points through the wire you've disconnected wouldn't you show continuity to ground through the coil itself?
 
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Old 11-30-15, 10:43 AM
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Not unless the coil is shorted out. Here is another diagram that shows it better.



While the coil is nothing more than a big resistor, the ground side of the coil comes from the positive side of the battery, through the coil/windings, to the points then to ground through the points. The only other path to ground is across the spark plug gap via the high tension lead.
In the case of the magneto, the positive is supplied by the magnet of the flywheels passing the coil, instead of a battery. While the magnetic field created by the magnets and or battery does produce a voltage, it is the "collapse" of the field that produces the high tension voltage required to fire the spark plug. The magnetic field/voltage collapses when the points open and break the closed circuit. If the wire to the points has a path to ground prior to the points, then the circuit can not be broken and thus, no collapse of the field in the coil.
 
  #19  
Old 11-30-15, 11:45 AM
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What I'm looking at is the first diagram at the magneto. That looks like the magneto coil is grounded through the coil windings. Isn't the second a different system with the battery/points/coil? The magneto generates the voltage while battery supplies an external source to the coil.
 
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Old 11-30-15, 12:43 PM
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That's exactly what I was looking for, it maybe awhile until I get to it.
Thanks.
 
  #21  
Old 11-30-15, 12:51 PM
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This engine has a 3 legged armature.
Geo
 
  #22  
Old 11-30-15, 02:05 PM
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Geo, bummer about the 3 legs, hope the rest helps...good luck and please let us know how it turns out.

marbobj,
As I mentioned the first diagram is just that, a diagram and basic. It does not show the internals that an engineering schematic would. Yes the second is a different system but they both work on the same principle. In the case of the magneto system, it is the magnets passing the coil that provides the low voltage that creates the magnetic field in the mag. The low voltage in the primary circuit is not what provides the voltage needed to jump the gap on the spark plug in the secondary circuit. In both circuits the coil does not provide the "low" voltage, it creates the magnetic field that when it collapses, produces the high voltage into the secondary circuit IE: high tension lead to the spark plug. In the case of the points system, if the circuit (path from the source of low voltage to ground + to -) is never broken the magnetic field remains and does not provide the high voltage to the secondary circuit.

It has been 28 years since I had the theory from my schooling as an A&P Mechanic, and while I have had just enough electronics to know there is a huge difference between a wiring diagram and a schematic, I also realize that chasing lil electrons where you can't see them, is a bit above my paygrade
Every complete circuit returns to ground...somehow. However, if you detect continuity, or zero ohms from the wire to the points to ground, then something is shorted out, because the resistance on a good coil should be between 7k-12kohms.
I have not worked on a points system in small engines or with a mag in some time now, but this is my understanding of the system and I have never failed to diagnose and correct one yet. I have however, recently worked on a points system like the second diagram, one was on a 57 packard the other on a 10HP Kohler on a 67 Cub Cadet (the second diagram is of a kohler btw) and in the case of the Packard, this was the exact problem. The wire in the distributor from the coil had worn insulation and was grounding out. I replaced the wire in the dizzy and voila...it made boom boom

I have enjoyed the discussion, and the fact that it has been just that, a discussion
I have refreshed and extended my knowledge on the subject and feel that my understanding is sound, even if I was not able to completely express it %100 correctly.

This is very old technology and sometimes, we as mechanics, just have to say ok, if it works, it aint broke so don't fixit


Az
 
  #23  
Old 11-30-15, 06:46 PM
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Just some added info and clarification of what I consider the difference between diagram and schematic, and chasing electron gremlins where you can't find em'.

Each of these exist in a typical small engine.

This is the schematic symbol for a capacitor (in a points system this is all the condensor is, is a capcitor)



Transistor (which replaces the points as a solid state in the magnetron/electronic magneto)



You will not see either or any other similar symbols in a wiring diagram.

Also as I talked about earlier, there are tests for these electronic pieces, however, I feel they can only be confirmed bad if they consistently fail the test. With solid state, temperature, humidity....etc. all effect these pieces with no moving parts. They can consistently test good, yet still be failing.
 
  #24  
Old 12-01-15, 05:29 AM
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Sounds like a winner. Have a great day!
 
  #25  
Old 12-01-15, 05:06 PM
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Mr.Grubb, I followed the procedure in the link,everything checked out and still no spark,I readjusted the air gap, checked the points again,seems like it must be the mag.
 
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Old 12-01-15, 05:27 PM
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. .
 
  #27  
Old 12-05-15, 11:54 AM
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WI Update

Hi All, after closing the points down to .018 the motor started right up,now I have the rehab the governor, nothing on it looks OEM. USAFLAG
 
  #28  
Old 12-05-15, 12:16 PM
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Success is a wonderful sound. Have a good one. Geo
 
  #29  
Old 12-05-15, 01:33 PM
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OEM is car collector stuff. If I can just get it to WORK I'm a happy guy.
 
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