What does this thing do...!? Carb question
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  1. #1
    Junior Member mcetp001's Avatar
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    What does this thing do...!? Carb question

    Hi all,

    I am wondering if anyone knows what this jet is? Is it an enricher/starter circuit jet?
    I have tried to find information here and on other sites but am having no luck.

    What does this thing do...!? Carb question-carb.jpg

    By way of background, I have a 1973 CB250 K with 725A carbs. It has had two previous owners; a farmer who bought it new to run into town for errands and the previous owner who was going to turn it into a cafe style. Long story short, he took it all apart and then lost interest. I bought it off his dad who had put it back together and got it running again but it wasn't running great. So I did the timing, valves, cleaned carbs etc and have it running very well except for one issue - it is hard to start.

    It takes about 8 kicks or the equivalent with the electric starter to get it going. I know that this is not atypical of a Honda but something just doesn't feel right and I like to tinker. It doesn't seem to make much difference with the choke on or off. Once it fires it doesn't like any throttle for a few seconds until it starts to warm up but it runs very well after that and pulls well through the rev range. Once it is hot it starts again first kick. This leads me to think it is a carb issue.

    I have rebuilt and cleaned the carbs a couple of times already and they were comparatively clean with just a minor bit of varnish in the jet and emulsion tubes (initially I forgot about the pilot jet under the rubber bung ) but I didn't have access to my compressor so probably could give it another once-over and start to blow all the passages out.
    Last edited by mcetp001; 07-10-2019 at 01:05 AM.

  2. #2
    Senior Member HerrDeacon's Avatar
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    I believe that hole is the bowl vent. You should be able to visually follow it to the outside top of the carb to see the vent there.
    Perry

    1972 Honda CB350
    / 1978 Honda XL250S / 1982 Honda MB5 / 2014 Honda CB500X
    Riding Through the Fog


  3. #3
    Senior Member TOOLS1's Avatar
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    I think you have a vacuum leak. Check the rubber boots between the carbs and head, Also the seals on the ends of the throttle shafts will go had and cause a running problem like this.
    TOOLS

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  5. #4
    Junior Member mcetp001's Avatar
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    Thanks guys - I will do some more investigating.

  6. #5
    Junior Member Mike1000's Avatar
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    That’s an air bleed, it helps fuel flow through the small carb passages, This sounds to me like late ignition timing check the point adjustment first then check the ignition timing If you’re able to advance the timing you’ll notice that the bike will have more snap when you hit the throttle.

  7. #6
    Supporting Member Yendor's Avatar
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    Herr Decan is 100% Correct.
    That is the VENT for the float bowl.
    Take a can of Carb Spray Cleaner to it and it will come out of the Brass Nipple on the other side.
    1970 CB 350 CAFE - Current Project on the bench,
    1972 CB 350 K4 Red - Now a Happy Rider ! !
    1972 CB 350 K4 Green (My Sons) DONE - YES !,
    1st Bike 1970 SL 350 (Brought home in Parts - Trailer/Trunk/Back Seat - I miss that bike),
    2nd - Bike Kawasaki 750
    3rd - '73 XLCH 1000

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