81 cb750 need help two carbs dead cant figure out why

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81 cb750 need help two carbs dead cant figure out why

CB2516
Okay, so ever since I got this its been running on 2-3 cylinders so I thought id take it apart finally, get the cleaned out and everything should smooth out.  Not the case, No. 1 and 2 cylinders do not hit.  However, if you hold your hand over the back they will (as if they're choked).  have checked compression all cylinders are good.  if you take the whole rail and let No. 1 & 2 stick out the left side so that No. 3 & 4 are on 1 & 2 cylinders they will fire.  I have spark proper gapping.  Have it timed (which was part of the bikes issue but has been corrected.  Blew air through all circuits and none seem clogged.  have had carbs apart 4 or 5 times now with them totally disassembled cannot find the issue, diaphragms in the air shutoff are fine.  I'm out of ideas... anyone have a suggestion?
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Re: 81 cb750 need help two carbs dead cant figure out why

shinyribs
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They're dirty and putting your hand over the back is increasing the vacuum signal to the point where they can overcome whatever restriction is in them. Even if they look clean, I bet if you try to blow through the idle passage that it is restricted.
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Re: 81 cb750 need help two carbs dead cant figure out why

TOOLS1
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In reply to this post by CB2516
I agree with Shiny. Your idle jets/circuit is plugged.
TOOLS
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1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
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Re: 81 cb750 need help two carbs dead cant figure out why

eric moon
There is a good write-up for cleaning the carbs

http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf

As stated, I expect your jets are still blocked. Blowing air will not dislodge all the crud.
1980 CB750F S/S
1979 CB750F
York
England