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Thread: ADDING TUNING PORTS

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    Adding tuning ports

    What is the general thought on adding vacuum syncing ports to the head of a CB450? I am meticulous by nature and like empirical feedback whenever possible, but Honda saw fit to not provide them on this bike. I am about to start final assembly of my head so now it the time to do it if I am going. Thanks in advance.
    Lee

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    Benevolent Dictator ancientdad's Avatar
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    Just my opinion but I find 2 carbs easy enough to sync without using vacuum gauges, but you can certainly put them in. I don't think that Honda did not see fit to provide them as much as, at the time, only the 4 cylinders had them prior to the 450's transition to the 500T.
    (move along, nothing to see here)

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    Senior Member Ribrickulous's Avatar
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    I looked into doing this on my 350, I believe the 450 also has very “short” intake connections where a port can feasibly go.

    Like AD says, you can get a reasonably good sync by hand and feel, which is part of why I decided to not go forward with it.

    If you do decide to go this route, I’d recommend trying to mill a flat in where you’re trying to get the port and using a screw and sealing washer while not syncing, so you’re not relying on a vacuum cap to not fall off during your ride.


    - 1972 CL350
    - 1985 VF700F
    Ed
    1972 CL350 K4
    1985 VF700F

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    I have also considered making a temporary standoff that has the ports and removing them after the tuning is done. Not ideal though because it will different than the installed state of the carbs and will also create turbulence which will impact how useful it is. I don't have an O2 sensor or anything so aside from some induction tachs on the coils, I don't have a lot of numbers to work with.

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    Benevolent Dictator ancientdad's Avatar
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    Quote Originally Posted by Ribrickulous View Post
    ...so you’re not relying on a vacuum cap to not fall off during your ride.
    Or blow off during an unlikely, but possible, backfire through the carb.
    (move along, nothing to see here)

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    Senior Member Ribrickulous's Avatar
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    I’m the same way re numbers. I loved tuning my interceptor because I have an induction tach and a set of vacuum gauges to work off of.

    I haven’t broken out an O2 sensor for the idle tuning on that one because it just feels like overkill, but now you’ve given me a new idea

    Nothing wrong with the route you’re going down, but on the twins you can keep it simple and get it working well.


    - 1972 CL350
    - 1985 VF700F
    Ed
    1972 CL350 K4
    1985 VF700F

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    Senior Member jensen's Avatar
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    I add two holes with thread for vacuum on every CB450 head, including the K0 I rode the last four seasons.
    <a href=https://www.vintagehondatwins.com/forums/image.php?u=26&type=sigpic&dateline=1663782826 target=_blank>https://www.vintagehondatwins.com/fo...ine=1663782826</a>
    CB450's (K0's, K1's, K2's), CB72'61-'67, all years, C77'64, CB400f '74, Kawasaki KR1-s '90

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    Senior Member Mikepacific60's Avatar
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    Hi all
    I decided to add vacuum ports to the head of my SL350K1 (the head of my bike is still with a machinist getting other work done, but I got it back temporarily to drill & tap the ports (M6) and add a clearance for the KA Performance tensioner I’m going to use).
    The ports are on the underside / inside of the head and I don’t think they will be visible.
    I purchased the fittings from 4into1.
    Once I have the engine running and balanced I have two options:
    1) connect the two ports - ie a ‘balancing’ connection; or
    2) connect the two ports as above, but block the connecting hose with a ball bearing - that way, even if there is a backfire, it won’t blow off the rubber port cover which is supplied with the fittings (a tip given by LDR).

    DCC13A82-5C56-427A-92E4-AF6BF78F7B51.jpg B5148EC4-DF72-448F-A4E8-AD0331D1E280.jpg

    Cheers
    Mike
    Honda SL350K1

  9. #9
    Senior Member jensen's Avatar
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    Yes, with the CB450 heads I made these connections in the same area, invisible for the un-trained eye.
    <a href=https://www.vintagehondatwins.com/forums/image.php?u=26&type=sigpic&dateline=1663782826 target=_blank>https://www.vintagehondatwins.com/fo...ine=1663782826</a>
    CB450's (K0's, K1's, K2's), CB72'61-'67, all years, C77'64, CB400f '74, Kawasaki KR1-s '90

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    I have decided to go ahead and do this as well. I am going to add ports at 4:30 on the right cylinder and 7:30 on the left cylinder, then spot face them for an M5 SHCS, add a copper sealing washer and lockwire the screw to the carb boot flange inboard mounting bolt. It won't be invisible, but it wont come loose either. Spot face tools are pretty expensive so I will probably end up making one.
    Lee

  11. #11
    Senior Member Ribrickulous's Avatar
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    Nice! Copper washers and a flat will work great.

    I don’t know your capabilities very well, but a machine shop might be able to do this for you cheaper than the cost of tools for you, and for less stress

    I’ve Got a mill available to me so would give this the old college try, but it’ll be tough to get the flat perpendicular-ish to the bore without the right tooling and alignment.

    Just my .02, but if you’re confident with it go nuts - and document it so we can all follow along!


    - 1972 CL350
    - 1985 VF700F
    Ed
    1972 CL350 K4
    1985 VF700F

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