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Carburetor

Carburetor Related
93 Topics 954 Posts
  • How To: Carburettor Tuning

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    NINJAN

    I found this vid on YT, which may be very helpful to those looking to tune their Mikuni carbs;

    https://www.youtube.com/watch?fbclid=IwAR2OspBdvJfZnFdVVttSrgyHoz3NxRYGmBDbIYmRem0HCbkKVO3nJ91yl1I&v=67Nb3DI-B3s&feature=youtu.be

  • dt 125 re carb inlet boost bottle missing

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    Hark_PtooieH

    The cylinder sucks in air at intervals, leading to a pulsation in the inlet airflow. That bottle is a buffer that smooths out the pulsations.

    The piston goes up, sucking in air through the carburetor which is (and should be) the main restriction in the intake. This causes a low pressure on the engine side of the carburetor, including that bottle.

    When the piston goes down and closes the intake port, there would be a rather sudden pulse where air rush in through the carburetor and meets a dead end. Pressure rises, gas stops throughout the manifold, including the carburetor. Then when the port opens and the piston sucks in gas again, it would have to accelerate the gas mass from zero.

    With the bottle, the volume of that closed-off manifold is artificially increased, so it takes longer for the gas to fill the cavity and come to a stop. Hence it keeps moving, supposedly until the port opens again and the piston suck in gas again.

    The effect should be that there is a more constant flow of air through the carburetor, which likely improves the atomization or decrease condensation or whatever.

    4-stroke engines usually tune the intake manifold runner lengths such that the air pulsations should cause the "pillar of gas" that comes at the intake valve at high speed should "ram" through it when it opens. While the mass of the air is small and it is very elastic, the velocities are substantial so it counts. I wager this is sort of the same thing.

    In 4-stroke engines it is also not uncommon that the intake runner lengths vary with engine speed. I know my car has a valve that opens and shorten the length above some rpms. My Honda Fireblade also had something like it in the airbox.

  • TM32 Flatslide carb

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    @OllieDTR

    I actually don’t think you need to ‘shave’ the rubber inlet at all. The 30 or 32 (can’t remember which) dellorto fitted to tzr’s just has a thinner wall where it fits into the rubber…
    Can’t speak for Mikuni though…

    You will have to do without it being angled to fit like the 28mm though. Shouldn’t be a problem though. I’ve had 30mm carbs fitted to Vespa’s that were mounted at horrific angles and still worked fine 🙂 We never used to bother with any air filter either, just a bell mouth on the Lambretta’s, maybe…

  • This topic is deleted!

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  • Where the rubber pipes go from carburettor

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    CalumC

    One is from the fuel tank to the fuel bowl on the carburrettor
    Two are overflow
    Two are carb warmer pipes from the cylinder head to the carb

  • Copy carbs

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    @BEng1968

    The angle isn’t ideal but in reality doesn’t affect running. I used to run 30mm dellorto carbs on lambrettas and Vespas . They used to sit at an angle but run fine

  • Carburetor size

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    CalumC

    Definitely want to restore that YPVS. This bike sounds to be in a bit of a sorry state 😞

  • DTR 125r 2000 full jet refurb Advice

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    CalumC

    @primal-carnage Better to just reference @scrimsmustang

    http://www.scrimsmustangclassicyamahadtrestoration.com/derestricting-the-yamaha-dt125r-1988-through-to-2007.html

  • TM28SS Float Bowl Powerjet Mod

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    @HOTSHOT-III
    I know an old hardtail fanatic biker who used to mod z1000’s and other bikes. He told me that RamAir used to make a foam filter kit for flatslide Mikuni carbs, included in it was a ‘jet correction’ kit that was a brass threaded insert for the power valve. You had to drill & tap the existing P/J casted hole and thread in the replacement.
    Interesting was that they didn’t recommend changing any other jetting on the carb...

  • Trying to fix an issue

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    CalumC

    @HOTSHOT-III That's a Rotax 122 Kart Engine

    alt text

    Let go at 14k RPM (maybe higher) probably when it went over a bump and the engine rev'd its nuts off without a limiter...

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  • DTR will only start with easy start

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    S

    You starter jets are both blocked by the sounds of it, the one on the carb body and the one in the float bowl. Common problem with none starting tm28,s

    Very old post but should help people who think these carbs are a nightmare when they have a starting problem with them.

  • Refitting carb hacks

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    Stevie WonderS

    Okay so I think I’ve solved it, if you cut away the tab/loophole that the coolant line at the rear feeds that’s attached to your air box (don’t worry everything still follows it’s original route and looks clean) you can then take off your battery tray and unbolt your air box and remove the whole system air boot included with absolutely 0 effort at all. To refit you simply the procedure in reverse, to fit it it all in you have to approach from the exhaust side and twist

    All that’s required is you remove your rear exhaust/silencer, rear quarter panels and seat

    I shit you not, what is usually a 45 minute job with lots of profanity is now a piece of piss

  • Lectron carb

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    M

    @SpookDog it is a a lot of money yes but they are suppose to be so good, look them up online on the reviews they are suppose to make the performance so much better, also takes the stress out of jetting been wrong on traditional carbs Ect, which I think is a pretty common problem on DTs is carb related problems

    The whole goal of my project is to build a old school looking two stroke but have a more improved or up to date component structure

  • Dep exhaust jetting

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    @spookdog
    I’m pretty sure everything’s on the stock set up on the carb although the pilot screw is at 1 and 1/2 turns out I’m planning on doing a top end rebuild and maybe getting the cylinder wall honed if it needs it but I’m gonna keep the standard 56mm bore also putting some boysen reeds in it to make it a bit more responsive

    my mates got a 1988 model with a hand welded pipe from Portugal and with reeds and no snorkel and I think he went Down to 230 main jet and standard on everything else so I’ll keep mine on the 240 and see what’s it’s like after I’ve done it he said the reeds make it a bit richer so may have to go down a few

  • Where’s Wally / The idle jet

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    @stevie-wonder

    I would check for massive air leaks around the carb & inlet, also maybe the magneto side oil seal. Especially if the revs are really ring-ting, ting, ting, ting fuel starved sounding...

  • Jd jet kit

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    declanD

    @skunkno1 I haven't heard of anyone running them but with how much people rate them in other bikes it's worth a try right?

  • When to re-jet

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    DTleeD

    @markus-w good shout, i use it every couple of months so ill give that a try as well.

  • Carb rebuild kit

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    @kevin
    Don’t know about Legend...

    Standard is 5j25 or 5j40. Don’t know if it’ll help you narrow it down? They both go with a Q2 needle valve though (tho the 5j40 is a Q2M)

  • Dt125 re

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    S

    @spookdog okay mate thank you , will have a play with it