Replacing diaphragm
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Thread: Replacing diaphragm

  1. #1
    Senior Member f100owner's Avatar
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    Replacing diaphragm

    When replacing the diaphragm with the original style does one use any cement to secure the replacement to the slide. I suspect when originally assembled, the diaphragm was simply placed between the washer and retainer and secured. But replacing, one must work the diaphragm into the space between the washer and retainer, so I am guessing there is potential for it to not be as secure and i have no idea how much pressure it is enduring. Guessing not much based on the spring.
    CL350K0
    2016 Harley Ultra Limited
    1971 Ford F100 Flareside (project)
    2016 Ford Expedition
    2018 Ford F150

  2. #2
    Super Moderator ancientdad's Avatar
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    The original replacement diaphragms were all one piece, slide and diaphragm as a unit. I've not personally replaced a diaphragm since they have been sold separately, I'd assume you'd follow the seller or manufacturer's installation procedure
    Tom

    CL450 project reboot, street legal this time
    Budget drag bike project
    CB350K1 full patina project
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    running points... because I'm too old for mysteries that begin with pushing

  3. #3
    Senior Member f100owner's Avatar
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    no direct documentation from manufacturer/seller was available that I could find at 4into1. Online searches obviously included the common motor approach - which I was not gung ho about trying and it used a different diaphragm without the tab. So I basically, removed the old with a blade, cleaned out the slot between washer and retainer and then worked in the replacement. Seems pretty solid.
    CL350K0
    2016 Harley Ultra Limited
    1971 Ford F100 Flareside (project)
    2016 Ford Expedition
    2018 Ford F150

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  5. #4
    Senior Member JamesPal's Avatar
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    I replaced the diaphragms on my GL1200. They came with a thick superglue to bond them to the pistons. On the 1200 there is a small pressure hole in the base of the piston. I'm not sure about the 350, but I believe the orientation is important. I put together this video about my 1200 carbs:

    Jim Palmer
    '85 GL1200I (Garage Find)
    '81 GL1100 STD (Project)
    CB450 K5 Done
    https://www.hondatwins.net/forums/1-...s-cb450k5.html
    What I learned from Restoring a CB450 K5
    Watch Mike and Jim Take on Mt Erie Washington State
    "If everything seems under control you are not going fast enough" Mario Andretti...

  6. #5
    Member doctorruckus's Avatar
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    Common-motor says to super glue them. Everyone else says not to. I would not. At most maybe use a flexible gasket sealer.

  7. #6
    Senior Member Twowheelrich's Avatar
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    Check out this website for replacement diaphragms and a wealth of info about fitment & installation

    JBM Industries Rubber Carburetor Boot Socket Holders & Diaphragms
    1973 CB 450 - Sold!
    1968 CL 175- up on blocks
    1991 KLR 250- 'Ol reliable
    2005 Suzuki Wee-Strom - just got it!

  8. #7
    Senior Member f100owner's Avatar
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    Did not use the Common Motor diaphragm, and replaced both of mine with ones from 4into1. Basically cut out the old and used a box cutter blade to clear out remnants between the washer and the retainer. Then worked in the replacements gently prodding the diaphragm into the space between washer and retainer. Of course made sure to get orientation correct so that two holes in slide base are at back/toward air intake.
    Bike is running much better. No lingering high throttle/idle. Rode it for about 1 hour through a variety of roads and it behaved well. Bike is not running perfectly by any means, but well for me. Someday would like to experience what a well timed/tuned one runs like.

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    JamesPal likes this.
    CL350K0
    2016 Harley Ultra Limited
    1971 Ford F100 Flareside (project)
    2016 Ford Expedition
    2018 Ford F150

  9. #8
    Senior Member JamesPal's Avatar
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    Good to hear it came out OK. I will never forget how my 1975 CB360T ran after I took it into the dealer for the 600mi check back in 1975. These bike are very sweet once they are in a proper state of tune. I always start by setting the valves, check the timing (I use electronic ignition) and then adjust the carbs. Valve lash will affect the carbs, that is why I do that last. Once you start getting it dialed in you will learn how the different setting affect each other. Enjoy!
    Jim Palmer
    '85 GL1200I (Garage Find)
    '81 GL1100 STD (Project)
    CB450 K5 Done
    https://www.hondatwins.net/forums/1-...s-cb450k5.html
    What I learned from Restoring a CB450 K5
    Watch Mike and Jim Take on Mt Erie Washington State
    "If everything seems under control you are not going fast enough" Mario Andretti...

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