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Thread: Vacuum Hoses ?

  1. #1
    CB750 Member old-drone's Avatar
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    Vacuum Hoses ?

    Hi, I am new here with a Question, I have this really nice 78 CB750k without Carbs, then i bought a set of Carbs but i can't figure out where all the Vacuum Hoses attach to.Does anybody have some sort of Diabram for these Carb set ups ? Thanks

  2. #2
    Moderator dirtdigger's Avatar
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    Where exactly are the vacuum hoses you are talking about?. There really isn't much for vaccum hoses, unless you are seeing the vent tubes?

  3. #3
    CB750 Member old-drone's Avatar
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    Hi, Thanks for the reply. I have one hose coming from the bottom of the Solenoid Valve, one coming from the Carburator next to the Fuel Line and one coming from the Air Filter Box, Where do they connect ? Thanks

  4. #4
    Moderator dirtdigger's Avatar
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    OK...did the bike have the solenoid valve or did it come with the carbs? Did you by chance get a carb set from the automatic 750? Any way you could take a picture of your setup? I dont want to guess at what you have and then be totally wrong as to how you need to hook it up.

  5. #5
    CB750 Member old-drone's Avatar
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    Hi, The Carbs come of a 78 Hondamatic 750a, they told me it would work jus fine.are they wrong ?

  6. #6
    CB750 Member old-drone's Avatar
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    Hi again, Sorry but i dont have a Digital Camera to take a Picture. I will try and see if i can borrow a Camera, and Yes the Valve and Air Filter Box came with the Carbs. The Person i got these from is moved Oversees and i cant get anybody locally to help me.

  7. #7
    CB750 Addict cyclebuster's Avatar
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    I just read they may have smaller intake size, so see if they fit your boots first, before investing in them. I am not sure if that big diapragm thing isnt just an anti stall dashpot assy. I havent seen a set in years honestly. BUT the do sell big on ebay, so you could clean them up, toss in a kit and score the extra cash to get a nice correct set.
    Last edited by cyclebuster; 11-07-2012 at 10:55 PM.

  8. #8
    CB750 Addict cafeken's Avatar
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    those cb750a carbs are not going to work for you the carbs are to small and wont fit your intake boots

    pm sent

  9. #9
    Moderator dirtdigger's Avatar
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    Yes the diaphragm is an anti stall dash-pot. I would get a different set of not automatic carbs as everyone else said. Looking on ebay you should be able to get enough out of your carbs to buy a decent set of correct carbs. Not worth the hassle to make these work on your application.

  10. #10
    CB750 Member old-drone's Avatar
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    Hi, Today i tried to mount the Carbs to the Bike and to my surprise the fit Perfectly but i still have the Problem with the Vacum Hoses, I would not mind keeping the anti stall Device on the Carbs if it could work.

  11. #11
    Moderator dirtdigger's Avatar
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    You will loose some power with these carbs they are smaller. The anti stall isn't needed on a standard 750, the automatic 750 needed it to keep the idle up when it was put into gear. I would think it would cause more of a problem on the standard 750, you wouldn't really want the idle to kick up while you are in gear slowing down or coming to a stop. You could run the carbs and just take the anti stall off but again you are still stuck with the detuned carbs.

  12. #12
    CB750 Member old-drone's Avatar
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    Hi, i just looked Back on my original Post and realized i made a mistake, it should have read CB 750A instead of K . Sorry about that

  13. #13
    Moderator dirtdigger's Avatar
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    So you have a Hondamatic?

  14. #14
    CB750 Member old-drone's Avatar
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    Hi, Yes that is what it is, I am totally new to the Multiple Carb Motor Bikes so You wil have to forgive me if i Screw up sometimes , i hope to get this Bike back on the Road again.

  15. #15
    Moderator dirtdigger's Avatar
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    No problem. You dont run across the automatics very often so most people dont have questions about them. There should be an electric solenoid. Bottom hose goes to the airbox. Top line is vacuum from the carb but there needs to be a checkvalve in the line. Side vacuum line goes to the dashpot.Click image for larger version. 

Name:	honda-cb750a-750-hondamatic-1977-usa-carburetor-solenoid-vlv_bighu0052e3221_5f4c.jpg 
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ID:	1493 See if this picture makes any sense for what you have.

  16. #16
    CB750 Enthusiast Bohnzye's Avatar
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    I'm voting for DirtDigger for...? You rock Buddy....

  17. #17
    Moderator dirtdigger's Avatar
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    No problem. Hope you get it running.

  18. #18
    CB750 Member old-drone's Avatar
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    Hi Dirtdigger and every body else for the help, I just hooked up the hoses like You said and put in some Fuel and pulled the Choke and she Fired right up and runs reasonably well, She wants to stall when i open the Trottle but when warmed up she runs OK, Thanks for the Help.Now i need to get a Synchronizer for the Carbs and i should be rolling in the Spring. lots of Time to Polich her up and lower her a little so i can reach the Ground, maybe some shorter Shocks and do something with the Front end.. Thanks again

  19. #19
    CB750 Addict cyclebuster's Avatar
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    is the air box on? the bog should go away with the entire air box installed.

  20. #20
    CB750 Member old-drone's Avatar
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    Hi, Yes the Air Box is on with a new Fiter but it still wants to stall when cold but is ok when Warmed up. Thanks

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