Pilot Jet, Main Jet, Starter Plunger... Ok now I know their name, but what are they?

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  • gjk0807
    #1

    Pilot Jet, Main Jet, Starter Plunger... Ok now I know their name, but what are they?

    Let me preface this thread with the fact that when I recently was given a motorcycle I did not know what the carbs did, or what they looked like. That being said, I have been doing research and a lot of learning but a few things still are stumping me.

    I have an 82 GS650Gl, it has been sitting outside for 2 years and I am now in the process of getting it back in road condition. I pulled the carbs off and have thoroughly cleaned them. The throttle valves now slide up and down freely, which took some work. I bought some rebuild kits but don't really want to rebuild until I have a firm understanding of what everything on the carbs are and what they do.

    A few questions I have are:
    What does the pilot jet do?
    What does the main jet do?
    What does the vacumm tube do?
    What is a starter plunger?

    Does anyone know of a good site with information that explains what all these things do and how they are related?

    thanks for any information or links to website with useful info
    Tags: carbs, main jet? starter plunger, pilot jeet
    • Dave8338
      Forum LongTimer
      Past Site Supporter
      • Aug 2006
      • 11608
      • Annandale, MN
      #2
      1. Is also called the primary, it is for throttle control from just off idle to midrange or1/2 to 2/3 throttle position.
      2. Is the jet that regulates fuel flow at WOT and back to about 2/3 throttle position.
      3. The vacuum tube I think you are referring to is for the vacuum supply to the petcock to opperate correctly.
      4. The starter plunger(or choke) is for cold start applications and supply an addition flow of fuel to assist cold starts.

        Comment

        • Steve
          GS Whisperer
          • Jun 2005
          • 35925
          • southwest oHIo
          #3
          A few questions I have are:
          What does the pilot jet do?
          You actually have two pilot jets for each carb. The pilot FUEL jet is down in the bottom, next to the main jet. The pilot AIR jet is in the intake to the carb (airbox side). Together, they pre-mix some air and fuel for your bike to use at idle and very low throttle openings.

          What does the main jet do?
          The main jet meters how much fuel is allowed to enter the air stream when the throttle is over half-way open.

          What does the vacumm tube do?
          Not sure which vacuum tube you are referring to, but if it's the one from #2 carb to the petcock, it turns on the fuel flow when the engine is running and turns it off when the engine stops.

          What is a starter plunger?
          The starter plunger is your "choke". There is no flap that covers the intake of the carb like there used to be on cars. By opening that plunger, there is a separate air passage and a separate fuel passage that are opened. They allow a very rich mixture to the engine for starting when cold. In order to use the "enrichment circuit" properly to start the engine, engage your "choke" lever under the left switch housing (probably about half-way), then turn the key ON, pull the clutch lever and push the starter button. DO NOT move the throttle.

          And you probably won't want to use those rebuild kits. Too many times, the brass pieces that you get are of sub-standard quality. It is far better to just clean your existing parts very well and re-use them.


          .
          Last edited by Steve; 06-20-2010, 09:47 PM.
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            Comment

            • BassCliff
              #4
              Greetings and Salutations!!

              Hi Mr gjk0807,

              You'll find lots of GS lovin' on my website, carb manuals, bike manuals, service guides, etc. I'm glad you found us. Let's get started.

              I just stopped by to welcome you to the forum in my own, special way.

              If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

              Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", the Carb Rebuild Series, and the Stator Papers. Now let me roll out the welcome mat for you...

              Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

              Thanks for joining us. Keep us informed.

              Thank you for your indulgence,

              BassCliff

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