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carb jet issues,

Discussion in 'XJ Modifications' started by Sal Raciti, Jun 22, 2018.

  1. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Drills actually aren't made undersize. Take a micrometer to one. The size they are marked is the size that they are (unless you buy crappy drills).
     
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  2. Polock

    Polock Well-Known Member

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  3. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Neither do I, and I never claimed that you do.
    This is the first 1/4" drill that came to hand out of my collection.
    [​IMG]

    Drills can, and almost always will drill slightly oversize from their dimension, but that's due to a combination of the type of fluting used (to allow for rapid material removal), tool flex, and whatever the inherent inaccuracy of the machine that the drilling is being done with is (chest bit, handheld electric drill, crappy drill press, good drill press, lathe, milling machine, etc.). When drilling a very small hole by hand, with a pin vice, very accurate holes can be easily made. The oversize (and honestly out-of-roundness) of a drilled hole tends to increase as the size of the bit being used increases (though there are other factors that cause the hole ot be oversize, as mentioned above).

    As for actual drill rod/bit size, that will vary due to the nature of mass production of disposable tooling (particularly consumer-grade stuff), but there is no standard (that I'm aware of) that calls for them to be intentionally made undersize while being stamped with anything other than the correct undersize dimension.

    I'll also withdraw my statement about crappy drills. While true, it's not just the crappy ones that can measure slightly differently from the nominal dimension stamped on the drill.

    TL/DR: Redrilling carb jets is a common, and longstanding practice. It works because the holes don't have to be drilled to absolute perfection for the jet to function properly.
     
    Last edited: Jul 21, 2018
  4. Polock

    Polock Well-Known Member

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    well sometimes i do.........did i ever tell you about the time......... :)
     
  5. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    LOL :)
     
  6. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    Yup.....
     
  7. Sal Raciti

    Sal Raciti New Member

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    So I got my bike to idle great and accelerate good with the 120 main and 43 idle, I know it's a little to big for a 650 but I'm still getting alot of popping when I let off the throttle. I always thought that was from being too lean. Everything else is fine except the popping. I was planning on going to a 118 main, and 42 idle until I heard the popping. What to do?
     
  8. Sal Raciti

    Sal Raciti New Member

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    Does anyone know if RamAir pods are any good? Or if they fit a 650? I wanted to get some better quality pods than the 10$ ones that don't really do anything.
     
  9. Minimutly

    Minimutly Well-Known Member

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    Buy some k&ns, take a knife to the sharp corners inside them, oil them and enjoy. Those cheap chinchong things don't even filter..
    No more to say really.
     
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  10. Minimutly

    Minimutly Well-Known Member

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    Old post I know, but:
    The one thing that makes the biggest difference - what size pilot or pre- final hole you use. If the finished hole needs to be 12 mm, you drill a 6mm pilot, then use a 12mm, you will invariably end up with a 12.2mm hole.
    However, if you drill a 11.5, then finsh off witha 12, you might get very close to 12, maybe 12.05.
    Just what I've found...
     
  11. Jetfixer

    Jetfixer Well-Known Member

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    My guess if it is popping your synch is off slightly you probably should start their .
     
  12. sybe

    sybe Active Member

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    Did you color tune each cylinder? Also uni pods or k&n are good. Buy waterproof pod prefilters for when it rains. Outerwears makes a good set for uni and i think k&n make their own.
     
  13. Sal Raciti

    Sal Raciti New Member

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    I just started to see some white exhaust on pipe #4, I assuming my rings are shot. It just started so Im thinking that's funking up my synch? All my valve clearances are correct, I only bench synced my carbs a month ago. Would the shot rings cause backfire?
     
  14. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    White smoke isn't oil. On an aircooled engine it's indicating that condensation is evaporating from inside the pipes.

    Popping on decel can also be from being too rich, and the excess fuel igniting inside of the exhaust pipes.
     
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  15. Sal Raciti

    Sal Raciti New Member

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    [QUOTE="k-moe, post:

    Popping on decel can also be from being too rich, and the excess fuel igniting inside of the exhaust pipes (just like flicking the engine cutoff switch will).[/QUOTE]
    Ok, that makes sense. It is like a fast firecracker popping. Thanks,
     
  16. sybe

    sybe Active Member

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    Kmoe is right. To know for sure how to proceed you need to colortune to make sure each cylinder has the proper air and gas mixture. This will help with poping and your idle.

    After you colortune it at idle you might notice after running the engine hot and at stop lights it will develope a slight hanging rev. The hanging rev is from running lean. If this happens you can either adjust your floats or put your hand over the tail end of your exhaust and feel the air flow. The side that is faster needs to get enriched via the air mixture screws. If both sides are fast increase all by small and even increments. Colortunes are great but with jets and pods its alil more tricky. Once you think its all dialed in put in new spark plugs and ride for an hour then read the plugs and adjust.
     
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  17. Polock

    Polock Well-Known Member

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    wtf?
     
  18. sybe

    sybe Active Member

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    Use the force...
     
  19. sybe

    sybe Active Member

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    If you are using 2 into 1 exhaust you can feel the difference in the rate of air flow if 1 or 2 are running lean vs 3 and 4. Try it. Run rich on 3 &4 and lean on 1 & 2 then feel the exhaust pressure. Its not an exact science and some might think inam crazy but it helped me isolate which side was running lean.
     
  20. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    That does work, unless you're using the stock exhaust setup. However, it's almost as tricky as synching four carbs by ear. Takes practice.
     

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