#38 pilot jet plugged solid (cb500t) - Page 2
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Thread: #38 pilot jet plugged solid (cb500t)

  1. #11
    Sensei 66Sprint's Avatar
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    The "illegible" mark is probably the Japanese initial or indicator of which factory worker produced that carb...(think paid by quantity of completed pieces)....Both carbs are 751A carbs

    Another consideration would be that supply to the slow jet would be the additive capacity of the transfer passage and the "drilled" jet......
    Fortunately, this would have a limited effect at idle as the fuel then has to go through the #38 slow jet as well......

    IT DOES become problematic as an additive volume once the main jet is in use as you would now have the additional fuel back-feeding FROM the through-drilled pilot jet, through the transfer passage to ABOVE the main jetting's restriction....(essentially increasing the size of the main jet)....
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
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  2. #12
    Senior Member WintrSol's Avatar
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    ^^What he said, which is why it is important to know if the transfer passage is even there, and whether the threads of the through-hole jet closes it. If it is not there, then you need two through-hole jets for the engine to idle properly.
    Rick

    Mine is a mostly 1970 CB450K3

  3. #13
    Sensei 66Sprint's Avatar
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    Rick....There IS a transfer passage and the 450's and 500T carbs ALL use the "plugged" type pilot jets......
    The threading of the through-drilled jets is NOT long enough to seal the passage........
    Which is why I offered one..........
    Last edited by 66Sprint; 09-16-2019 at 07:22 PM.
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199

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  5. #14
    Senior Member tbpmusic's Avatar
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    Quote Originally Posted by jml View Post
    I went out to compare and here's what I found. The pilot jet without the hole is a #38 with a manufacturer's mark on it, and is in a carb body stamped "NF<illegible> 751A". The pilot jet with the hole through it is also a #38 and has the same marking on it, and is in a carb body stamped "NFL 751A"; this is the carb with the choke lever (I may have gotten that part backwards earlier). Does this help clarify anything?

    Attachment 290700Attachment 290698
    That hole looks bigger than 0.38 mm to me.
    And when I think about it, I don't recall seeing that jet with a hole in it on any 450.
    Bill Lane
    Honda Twins Founding Member

    No advice, just info

    '75 CB200T, '71 CB450 K4 Half-Breed, '72 CL350 (Sold), '81 CM200T, '72 C70M
    and a little red Chineeze scooter

    http://www.bikeexif.com/honda-cb450-restoration

  6. #15
    Senior Member WintrSol's Avatar
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    Quote Originally Posted by 66Sprint View Post
    Rick....There IS a transfer passage and the 450's and 500T carbs ALL use the "plugged" type pilot jets......
    The threading of the through-drilled jets is NOT long enough to seal the passage........
    Which is why I offered one..........
    So, you're saying that, in this regard, the 751A carb IS a standard 450/500 carb, and is mostly the same internally as the 723? Something for the memory bank, in case it comes up again.
    Rick

    Mine is a mostly 1970 CB450K3

  7. #16
    jml
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    Thanks, all. This has been a fascinating thread, and I'm glad I was able to spark some discussion and learn some things. I'm definitely going to take 66Sprint up on the offer of the jet. If things get weird after I install it I'll update here.

  8. #17
    Sensei 66Sprint's Avatar
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    Quote Originally Posted by WintrSol View Post
    So, you're saying that, in this regard, the 751A carb IS a standard 450/500 carb, and is mostly the same internally as the 723? Something for the memory bank, in case it comes up again.
    Only if you ignore different jetting and air-cut valves....751A is only used on the 500T (that I know of offhand)
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199

  9. #18
    Senior Member tbpmusic's Avatar
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    Quote Originally Posted by 66Sprint View Post
    Only if you ignore different jetting and air-cut valves....751A is only used on the 500T (that I know of offhand)
    I think you may be right about only being used on that model, Steve. Not sure what early Goldwings used, their carbs were very similar, except for the obvious linkages. In fact, the air cutoff thingies are the same parts on 500T and GW 1000's.
    I haven't worked on a lot of 500T's, and can't remember if that jet was drilled or not, never noticed.
    Attached Thumbnails Attached Thumbnails #38 pilot jet plugged solid (cb500t)-capture1.jpg  
    Last edited by tbpmusic; 09-17-2019 at 09:34 AM.
    Bill Lane
    Honda Twins Founding Member

    No advice, just info

    '75 CB200T, '71 CB450 K4 Half-Breed, '72 CL350 (Sold), '81 CM200T, '72 C70M
    and a little red Chineeze scooter

    http://www.bikeexif.com/honda-cb450-restoration

  10. #19
    Senior Member WintrSol's Avatar
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    Quote Originally Posted by 66Sprint View Post
    Only if you ignore different jetting and air-cut valves....751A is only used on the 500T (that I know of offhand)
    OK, good, for future reference. I've never worked on a 500T, and don't have a parts list for one - guess that's obvious. I knew about the valves, and jetting seems to vary with each carb version, but never knew what the stamped number is.
    Rick

    Mine is a mostly 1970 CB450K3

  11. #20
    Senior Member pattyandrick's Avatar
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    The jet with cross holes is plugged at the bottom and the actual jet is on the top toward the body

    Sent from my SM-J320V using Tapatalk

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