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  • #61
    Hi johnu, i am assuming its a concentric carb, if it is, some of these carbs had there pilot canal drillings at a standard size & no matter how large you go with a pilot jet, it won`t make any difference as the standard drilling size reduces any effect a larger pilot jet might have.
    But it does sound like you have an air leak, or its very weak ( fuel to air ) if its external, easy way to find it is to run the engine, create the same poor running symptoms, then spray wd 40 around the manifold area, the revs will drop straight away if a leak is present.
    But the concentrics were notorious for wear on the lower slide area, when worn,the air is drawn around the slide, rather than underneath it.
    But don`t despair.....find a suitable bin...throw it in & fit a 34mm mikuni quality carb like everyone else..............

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    • #62
      Originally posted by dave higgins View Post
      Hi johnu, i am assuming its a concentric carb, if it is, some of these carbs had there pilot canal drillings at a standard size & no matter how large you go with a pilot jet, it won`t make any difference as the standard drilling size reduces any effect a larger pilot jet might have.
      But it does sound like you have an air leak, or its very weak ( fuel to air ) if its external, easy way to find it is to run the engine, create the same poor running symptoms, then spray wd 40 around the manifold area, the revs will drop straight away if a leak is present.
      But the concentrics were notorious for wear on the lower slide area, when worn,the air is drawn around the slide, rather than underneath it.
      But don`t despair.....find a suitable bin...throw it in & fit a 34mm mikuni quality carb like everyone else..............
      Thanks Dave! It could be wear in the carb body causing trouble because there are definite signs of wear. I will try the wd40 trick but i'd be surprised if there is a leak on the manifold as I sealed it with silicone gasket sealer.
      I might just go to the Mikuni, I already have them on other bikes so I could just try one on the Greeves. Would you be able to give me a base setting for the Mikuni, jet sizes etc?

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      • #63
        Any mikuni dealer/agent will hold the data for a griffon, i forgot that yours is 250, so i would speak to them to find the correct size.
        Over here in good old blighty, you can order a new unit jetted to suit, for approx £110, so its not to bad & then all your problems will melt away.....have fun....

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        • #64
          Johnu, it might be worth checking your crankshaft oil seals to ensure they are not leaking. Leaky oil seals produce similar symptoms to those you are experiencing. Even though you have no doubt fitted new seals, they sometimes leak.
          John A - 268

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          • #65
            Originally posted by John-Boy View Post
            Johnu, it might be worth checking your crankshaft oil seals to ensure they are not leaking. Leaky oil seals produce similar symptoms to those you are experiencing. Even though you have no doubt fitted new seals, they sometimes leak.
            Thanks. For sure have new seals in there, hoping I don't have take the engine apart already!

            Dave no such luck in the USA with Mikuni setting the carb up for the Greeves. I bought new mikuni's for my T500 and no one would supply them with a baseline setup for the bike. They ask you to spec the jetting you want I might just have my dad get me one in the UK.

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            • #66
              Ok getting pissed off with this issue. No leak around the manifold I tried the wd40 trick. Took the carb off and made sure everything is clear in there. There is a bit of wear in the carb but it doesn't look significant. The big question mark for me is that it ran quite well the first couple of times I started it then the next time it has this issue with the revs not dying down. I have a feeling something has happened to one of the crank seals
              Dave I know you said about changing to a different carb but they must have run half decent on the Amals. I think my dad has another carb body I can try.

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              • #67
                Ok lads I gave the Mk1 concentric one more try. Took it apart cleaned everything and put the 25 pilot jet back in. Everything on the carb is new except the body and the top cap. Well it was even worse She started up on the third kick and I let it tick over for a bit to warm up before I adjusted the airscrew. Give it a couple of little revs still the same issue with the revs dying down very slowly. Then the next rev it didn't die down it was at about half throttle then it just went up to full bore. I had to hook the ht lead off a bit sharpish
                So no more messing around I'm going to splash out and buy a new carb

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                • #68
                  Ok guys, i just want to let you all know that regretfully I won't be racing the Griffon after all I am planing to race the Baja 1000 and also the Pikes Peak hillclimb the following year and those are both huge commitments along with racing supermoto. I want to do everything but I only have so much time! So I have decided to get rid of a couple of bikes as they take up room that is needed in my shop.
                  I wanted to thank you all for all of the technical help you have given me it was much appreciated. I am not out of the Greeves club entirely though as I still have my Scottish which I will never sell for sentimental reasons.
                  Ken Sykes will be putting the bike up for sale on his Greeves page on facebook and I will be advertising it locally.
                  Thanks again,
                  John.

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