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  1. #1

    Join Date
    Nov 2011
    Posts
    3
    Location
    Ohio
    Mower
    Craftsman

    Advice - No Spark, Briggs 20.5 HP twin cylinder

    Some advice for no spark problems.

    I had a coil go bad in my Briggs engine.
    The symptoms were as follows:
    - Progressively hard to start when engine is cold
    - Progressively harder to start when engine is hot. Sometimes impossible to start
    - Misfire at idle and consistently at full throttle
    - Smell of gas when running and smoke when throttling up
    - Eventual full failure to start

    Diagnosis:
    - Initial impression was that the card was running very rich and flooding the engine
    - Checked spark by pulling plug on both cyliders. Result: No spark.
    - Ohm meter showed infinite resistance between coil leads and each lead and any coil terminal (this is a meaningless test, though I did not know at the time, on this particular coil in spite of what anyone may state). I performed a sanity check on a lawnmower coil and it ohmed out exactly as I would have expected. Same for a coil on a snow blower.

    Course of correction:
    - Installed new aftermarket coil: Result: Engine ran but hard to start
    - Tested new coil. SAME RESULTS AS BAD COIL. Infinite resistance, etc. Thought I had a bad new coil...but I did not.
    - Disconnected kill wire from coil to assure no intermittent shorting. Result: no change in symptom
    - Verified that engine crank speed was good. How? Just a fully charged battery and knowing what the sound of a fast turning engine is like. If you have started enough engines you know this sound.
    - Re-seated all safety switch connectors. No change in symptom. Assumed that the switches were good since I could crank the engine and also since when it did start, it never just shut off.
    - Checked spark. Result: weak but it did spark; apparently just not enough to allow easy starting
    - Thought that I had a weak coil...this was nor the case
    - It's all about the air gap...
    - After some reading I found some loose guidelines regarding the distance between the coil armature and the flywheel. I found that a brigs coil comes with a sheet of paper that tells you to set the air gap between the coil armature and the flywheel to 0.010 or about the thickness of three sheets of paper. With this info I examined the air gap. It was around 1/16 of an inch. I loosened the coil and spun the flywheel until the magnets pulled both ears of the coil armature against it. Then I pulled the coil back and inserted my 0.010 feeler gauge between the flywheel and the armature Then tightened. I assured that both ears were at 0.010 after tightening the coil.
    - I cranked the engine and it immediately started. It ran smooth.


    Lessons learned:
    - When coil was going bad, it seemed like an out of adjustment carburetor
    - When coil failed, the go to test for most coils DID NOT apply to this coil. So, infinite resistance = bad. Well, not in this case. Ultimately, the original coil was bad but confirmed by lack of spark when engine was cranked and the the kill wire was disconnected.
    - AIR GAP. This was crucial to the entire equation. I have read many posts of people putting in new coils and going bonkers because the engine will not start. This in spite of them having run down through a laundry list of tests.

    Advice: Set the air gap when installing a new coil. While the difference between 1/16 of an inch and 0.010 may not seem like that much to a person, electrically this is significant.

  2.  

  3. #2

    Join Date
    Sep 2011
    Posts
    172
    Location
    North Carolina
    Mower
    Walker

    Re: Advice - No Spark, Briggs 20.5 HP twin cylinder

    use a business card or old piece of micro fiche for the correct air gap, much easier and quicker than a feeler gauge and works great, never had a problem with either one.
    If a hammer doesn't fix it then you have an electical problem.

  4. #3

    Join Date
    Feb 2012
    Posts
    5
    Location
    Washington
    Mower
    Wards & Craftsman

    Re: Advice - No Spark, Briggs 20.5 HP twin cylinder

    Good article and advice, thanks

  5. #4

    Join Date
    Jan 2012
    Posts
    69
    Location
    Kentucky
    Mower
    Cub Cadet Yazoo Craftsman

    Re: Advice - No Spark, Briggs 20.5 HP twin cylinder

    Yeah...that business card thing works out pretty good in a pinch.I do that quite a bit!!!!jc

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