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spark per rpm

Discussion in 'Lawn Mowing' started by odin, Sep 9, 2002.

  1. Any one know if a vtwin kawasaki 4 cycle air cooled fires 1 spark per rpm or is it 2 sparks per rpm.

    I got a new tach and i need to set the mode for either 1 spark per rpm or 2 sparks per rpm
  2. Floridalandcare

    Floridalandcare LawnSite Senior Member
    from Tampa
    Posts: 314

    I would think 2sparks per RPM. Not too sure
  3. KLMlawn

    KLMlawn LawnSite Senior Member
    Posts: 443

    Well, I am not a mechanic, but I think most mower engines are supposed to run in the high 3000's, between say 3600-3900 no load RPM. So try it both ways, if one setting is giving you only say 1800-1900 at full throttle with the blades off, then it must be the other setting .....
  4. 1 spark to 2 revolutions 4 cycle.

    Intake, compression (spark) power, exaust.

    2 cycle, 1 spark to 1 revolution
  5. EJK2352

    EJK2352 LawnSite Bronze Member
    Posts: 1,150

    That engine fires twice per revolution, once on the compression stroke and once on the exhaust stroke. The only small 4 strokes that fire once per revolution are ones with a distributor and Kohler K series with points. If you set the tach for 1 spark per revolution, the tach is going to show an RPM reading that is half of the actual speed. :) ;) :) ED
  6. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    The plug(s) fire once on every revolution. The magneto(s) (coil assembly) is fired off of the flywheel unless the engine has a distributor. It doesn't matter whether it's 2 stroke or 4, small engine or large (this usually only applies to outdoor power equipment engines).

    Even the Ford Modular V-8 engines fire on every rev until the computer figures out which stroke the cylinder is on. And yes, they are crank triggered.
  7. awm

    awm LawnSite Gold Member
    Posts: 3,354

    well now . i was pretty much thinking along the lines of what lgf said.
    thought that was pretty much the way it was.ill have to look into it, first chance.
  8. Yeah that's right the second spark is a waisted spark on the exuats stroke.;)
  9. Well i set the mode on 1 spark per rpm and got four different engines to 3760 under no load without the blades on.

    Tryed the 1 spark per two rpms and it was half that and i tryed the 2 sparks 1 rpm and it was half that to.
  10. awm

    awm LawnSite Gold Member
    Posts: 3,354

    richard ,what u doing in lawncare,man.
    what u need is a garrage with several bays.:D :)

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