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Primers vs. Chokes

Discussion in 'Chainsaw' started by bplust, Jan 28, 2011.

  1. bplust

    bplust Addicted to ArboristSite

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    Hi all,

    What are the advantage/disadvantages to each one? My intuition tells me that a choke would last longer than a pump, but I've been wrong before.

    I'm sure this question has been asked before, someone redirecting me to a previous thread (I couldn't find what I wanted) would work.

    Thank you,

    Bryan
     
  2. brages

    brages Addicted to ArboristSite

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    As far as I can tell, the "primer" on most *** is basically a "purge pump" that gets the carb full of gas without having to pull the starter cord. So more "first-pull" starts.

    However, even saws with this "primer" need the choke to enrichen the mixture enough for it to start.

    In my limited experience, *** without primer bulbs start better than *** with...
     
  3. Eccentric

    Eccentric Mister Wizard

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    You're basically right. Most of the bulbs you see on small *** (chainsaws, hedge trimmers, blowers, whackers, etc) are indeed purge pumps (and not primers, despite what people call them). They push or pull fuel through the lines and carb, purging the air out. Makes for quicker starts. The downside of 'em is that they tend to develope air leaks after a while. I'm not a fan of them. Just my opinion, based on my experiences...

    True "primers" on small *** are usualy piston pumps that spray a shot of fuel into the carb throat or intake manifold as a means of enriching things for cold starting in place of a choke. You won't see that on much 'modern' small ***. Back in 'the old days', McCulloch chainsaws were where you'd find the most primer systems. Many lawmowers do still have bulb type primers in place of chokes.

    A purge pump can be pressed 100 times without flooding the engine. Once the air is purged, all you're doing is passing fuel through the lines and carb and back to the tank. The bulb feels 'harder' to push once the air's out.

    A primer bulb or pump will flood the engine if it's pressed too much. For the most part, you won't find a primer on a piece of *** with a choke. You will find a choke on a purge pump/bulb equipped piece of ***, as it still needs some method of cold start enrichment.
     
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  4. drkptt

    drkptt ArboristSite Operative

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    That's spot on. In addition to air the metering chamber can also have a fuel vapor bubble, especially after heat-soaking when a hot saw is shut down. The purge pump will pull that through as well.
     
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  5. CGC4200

    CGC4200 Addicted to ArboristSite

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    last saw I heard of with a primer

    I have a Makita DCS 520, just a choke, the 520i had an prime injector
    carburetor, think some Dolmar i models did too.
    I have some *** equipment with purge bulbs, when working properly, they seem
    to help starting by flushing stale fuel out of carburetor, but more lines & a flimsy
    bulb to crack & fail.
     
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