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Could it be the carburettor??

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    Could it be the carburettor??


    My friend has recently bought a 400 Bros. It's his first bike (just passed his test), in good condition and to date has started first time, every time and has been running really well until a few days ago....

    Now it will start but you need to twist the throttle and keep it on for it to run. It sounds really 'lumpy' (best I can do for a description, sorry!) and if you let off the throtte the engine dies.

    Now neither of us are very mechanically minded (still learning what is what) and my trusted mechanic is not available for another couple of weeks so I thought I would ask for any advice or suggestions.
    The best way I can describe it is that it sounds like somethings blocking the flow of I don't know what, air, fuel, something??!?!

    Fumes are coming out of the exhaust (I did wonder if something was blocked in there but I guess not) and it's not black and smokey or anything like that. We haven't left it running for long though in case it made the situation worse.

    It has been suggested that it may be the carburettor? Does this sound like a possibility? If so is it something we are safe to fiddle with (we have a manual!) or should we wait for the mechanic?

    I know it may sound daft but we want to learn so I would welcome anyone's input and advice before we just ship it off to the garage

    Many thanks and best regards to all,


    I could be a couple things I am thinking...

    Clogged jet or even fuel filter... It doesn't seem to be getting enough fuel... The filter should be easy, you have to follow the line back to the pump, remove filter and see if you can see any gunk in there, if so replace. If not then the carbs could be gunked up or something could be clogging a jet, (did the bike sit for a long time?)

    Or it could be...
    There is a black knob under the left side of the tank attached to the carbs, that is your idle speed adjuster, try to twist it until it will idle. Maybe that is it.

    Let me know how it turns out. It is difficult doing this Via internet.
    BIKES: Honda: RC31 Racebike/ NT650 Streetbike, DUCATI: None at the moment.
    Former MSF Rider Coach / Trackday Instructor/ Expert Roadracer #116
    "I'd rather ride a slow bike fast than a fast bike slow."


      sounds lumpy, smokes alot, gets worse as it runs.

      You're most likely running really rich, or one of your cylinders isn't firing. I'd check for spark. There are two plugs per head on the 650's... dunno for the 400's. The plugs could have gone bad, the plug wires may be on their last legs, maybe a bad coil (I've never had a coil go bad on me for five bikes... knock on wood).

      I'd suggest not to dig into the carbs just yet.
      It's scary how slow I am!

      '88 HawkGT - crashed as all hell - Hiperform subframe, VFR rear wheel, F3 front end, Penske shock.

      '05 Ducati S2R - Monstrack mirrors, CRG levers, Evoluzione clutch slave cylinder, ProItalia tail chop, Arrow damper, Nichols flywheel, Suburban Machinery bars


        Thank you both for your replies...

        Strangest thing happened - last night it started and ran fine.Yet it hasn't for days.. odd.

        We'll give it a small run out today and see how it goes... if it runs ok today maybe is was just a clogged jet or something that has cleared itself.

        We shall see..... will update you next week, in the meantime have a great weekend

        Thks & BRgds


        p.s. Kennie - the video clip - is that you? Scary!!!


          That's our mate Max biaggi isn't it? What a brilliant rider even if he is a F*%kwit.


            See if adjusting the idle upward works. If not, check the choke to make sure it's working properly. If it is, you could try running some carb cleaner through the tank. If that doesn't work, check the fuel filter. If that doesn't work, pull the carbs, disassemble them, and clean them with a needle.

            Check the tank for rust too.
            '88 Hawk GT - back in the saddle
            '99 Suzuki GZ250 - the first

            '87 Suzuki GSXR1100/1207cc - traded to get my Hawk back


              Dear All

              Thanks to everyone for their advice - the bike seemed to recover on it's own so maybe it was a small blockage somewhere. For days it wouldn;t idle/keep running and then one day it seemed to sort itself out!!

              It is now with the mechanic for a full service and some tlc.

              Best regards