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‘Mystery Vacuum Line’? (rear cylinder intake port to rear carb body) Non-Cali Hawk

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  • ‘Mystery Vacuum Line’? (rear cylinder intake port to rear carb body) Non-Cali Hawk

    I’m looking for info about a ” vacuum line from the rear cylinder intake port to the rear carb body on my non-Cali Hawk.
    The front cylinder head intake port has the same fitting but it’s capped off and the front carb has no connection for this type of vacuum line.
    My best guess is that a P.O. mixed and matched Cali parts and non-Cali parts. It would be nice to get some feedback from the forum, especially from folks familiar with their stock Cali set up. Ideas?

    I started by checking with the P.O.. No help there.
    I looked at the drawing on the bottom of page 1-15 of the manual and got the idea about Cali vacuum lines running from the intake port to the Air Vent Control Valve (AVCV), then back to the carb (Cali only). My Hawk doesn’t have any of the Cali stuff, so "mixed and match carbs" is the best theory I’ve got.

    The bike WAS running well for the year I’ve owned it…but lately…not so much. That’s what sent me digging into the carbs after eliminating all the usual suspect sources of crank-no-start…(not even a cough unless I squirt some fuel into the carb intakes). I’ll be doing a thorough cleaning on both carbs later this month.

    I hope the attached pictures fill in the blanks where my words didn’t do the whole job.


    Attached Files

  • #2
    cali carbs, the line should be plugged. photo at right shows vacuum tap for synchronizing, must be capped off for bike to run right.
    "It's only getting worse."

    MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

    Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.


    • #3
      Thanks for the info. I'll cap both vacuum nipples (rear head and rear carb) when everything goes back together in a few weeks...waiting for parts.
      Will let you know how it works out.