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  • MX3 Challenger Carb question

    Good afternoon

    I am getting my 250 Challenger ready to race this season and I decided, after some advice of fellow owners, that for ease of tuning that I wanted to use a Concentric rather than a monobloc. My bike is a one-owner unit that came with original service notes and a box of spares. In the box of spare was a labeled bag that contained a concentric carb, and was noted to be jetted for the Greeves. After a thorough cleaning and a new float bowl to replace the slightly warped one, i installed it along with a new cable. The bike revs fine, and I am still adjusting some things overall to be able to really test it....but this particular carb has a four stroke venturi/sprayer. Is it possible that it will run fine with this setup? Could it be possible that the original owner bought the wrong carb and then put the monobloc back on after he couldn't get it to run right? I have ordered a brand new amal premier two stroke...but while I wait for it I want to know if I am spinning my wheels by attempting to tune essentially the wrong carb.

  • #2
    There are people much much more qualified to give you an answer than me but my gut thoughts were, could you put it on a dyno and see what it gives out with the current carb. If its better than stock run with it. I'm sure there must be folks out there that have experimented with differing carbs and found extraordinary improvements. There again if you are a purist then you may want to stick with the originally conceived design. I recently bought a Hawkstone that has a BMV carb fittied. Not sure if this was intended as an experiment or just stuck on at point of sale as the bike is a massive restoration in waiting...
    As an addendum - Ive found its best to join the GRA as a full member, that way you can access all areas of expertise. - 'Come on in, the waters fine'
    Last edited by MarkM; 01/02/2018, 01:48 AM.

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    • #3
      Originally posted by MarkM View Post
      There are people much much more qualified to give you an answer than me but my gut thoughts were, could you put it on a dyno and see what it gives out with the current carb. If its better than stock run with it. I'm sure there must be folks out there that have experimented with differing carbs and found extraordinary improvements. There again if you are a purist then you may want to stick with the originally conceived design. I recently bought a Hawkstone that has a BMV carb fittied. Not sure if this was intended as an experiment or just stuck on at point of sale as the bike is a massive restoration in waiting...
      As an addendum - Ive found its best to join the GRA as a full member, that way you can access all areas of expertise. - 'Come on in, the waters fine'
      I am a full member, I just recently joined but my forum credentials haven't been changed yet. I am being patient. Thanks for the reply.

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      • #4
        You need to e-mail Rob Thornton to get full access to all parts of the Forum, unfortunately, it doesn't happen automatically.

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        • #5
          Amal Carb Tuning and Specs Info.....

          This has come up before.....Chairman Rob also did a load of research into this area and it eventually appeared as an article in 'LL' a while back.

          In the meantime this article, originally posted by Kim 275 in a previous thread, should go some way to answering your query.....https://www.princeton.edu/ssp/65-cub...albritbike.pdf

          There is other useful related info on that same thread, as started by Soggy Welly (Paul), so here is a direct link to that as well; http://www.greeves-riders.org.uk/for...carb#post34013

          Start around post 17 and Kim's article link (as above) appears in post 18, but do check out the rest of Paul's thread as well.

          Finally......just a thought......Dyno rollers and knobblies are a bad mix...!

          If having read this anyone may be thinking of putting a Greeves scrambler on a dyno, PLEASE make sure you fit a suitably sized ROAD tyre to the rear wheel.....I'm not joking.....

          Anyway, good luck with the rebuild Mr Petersen, and hope the above links prove helpful to you.

          Brian.
          Last edited by Brian Thompson; 01/02/2018, 07:51 PM. Reason: Links added and spelling.

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          • #6
            Thank you very much Brian! I have a brand new 2t Amal ordered, so in the meantime I will mess around with the one I have. Good reading material.

            And Mr. Catt, I have contacted the governing powers requesting full access twice so far, just waiting on that. Working on these classic machines has resulted in one very developed character trait, patience. So I will keep being patient. Thank you again for helping me in my membership!

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            • #7
              Loren - see your other post - you are upgraded!

              I think the main reason for 2 stroke and 4 stroke carbs was that many years ago, a modification kit for 4 strokes was introduced to overcome various isssues and what was left became the '2 stroke carb'. The main difference is that the 2 stroke needle and needle jet meters at the top of the needle jet and the 4 stroke at the bottom. That is why the 4 stroke needle is longer than the 2 stroke. Fairly obviously, you need to ensure you have 2 of a kind in the carb or things will be haywire!

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