1982 CB450SC jet sizes
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Thread: 1982 CB450SC jet sizes

  1. #1
    Member mikemo's Avatar
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    1982 CB450SC jet sizes

    Bike is an 82 CB450SC Nighthawk. I was hoping to get some help from the list on some oddities that I'm finding. Bike is new to me, with 9000 miles on the odometer. The PO said that the last time it was "worked on" that the mechanic said that the carbs were "finicky". When I turned on the gas, the carbs both leaked out of the drains and the accelerator pump housing, so I made sure it started and ran (poorly, but it ran on both cylinders), so now it's time to clean the carbs and get them right.

    I got the carbs off the bike this afternoon and took a preliminary look. It's no wonder that they didn't run well. The o-rings on the air valves were missing, the accelerator pump was clogged (and leaking while on the bike). Throttle plates massively out-of-sync. Choke plates out-of-sync (bent actuator). One pilot screw all the way in, one out 5 turns. Yikes.

    What has me puzzled is the installed jet sizes. The carbs are VB22G

    Main primary: 72
    Main secondary: 102
    Pilot jet: 35
    Needle: D329

    These sizes all seem quite a bit smaller that what should be there stock. I'm going to keep the stock airbox/filter. What sizes should I use to replace the above jets?

    Does the Honda gasket kit for these carbs come with the air-cut valve o-ring, or do I need to buy complete air-cut rebuild kits. The diaphragm on the ones in the carbs now seem fine.

    Also, looking at this pic, should there be a rubber plug on here somewhere? The FSM shows a picture that points to a "slow jet plug" but the pic is hard to see. Am I missing this plug?

    1982 CB450SC jet sizes-dscn0787.jpg

    Also, any idea why someone would do this to an airbox? It looks like they locked a hungry rat in there and made it chew its way out:

    1982 CB450SC jet sizes-20190824_163212.jpg

    One other thing too. I noticed that when I removed the jet marked 72 (primary main?) that there looked like something underneath it that could be unscrewed and removed. I didn't have a screwdriver that fit, so I haven't touched it yet. What is that under there?

    Thanks in advance for any help guys. I appreciate it. I know it's riding season for most.
    Regards,
    Mike M.

  2. #2
    Super Moderator J-T's Avatar
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    Here's the low-down on the jets:

    https://www.hondatwins.net/forums/63...ting-more.html

    You should have 72/115 main jets and a 38 slow jet (not sure if your slow jet is removable, I think it is). Keihin jets are widely available from places like jets-r-us. Do not buy an aftermarket kit that says it has the proper jets, they won't be.

    Yes, that o-ring is included in the Honda gasket set, part # 16010-413-405.

    Don't know about the needle.
    JT
    81 CM400T

  3. #3
    Super Moderator longdistancerider's Avatar
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    The needle, D329, is from some aftermarket kit. Honda needles are marked as 2 numbers and 1 letter. I'd suggest finding some 61C needles, pretty hard to come by but best for your model.
    Yes. you should have a rubber plug, included in the Honda gasket kit.
    This thread will help you out https://www.hondatwins.net/forums/63...tin-carbs.html

    Oh, forgot to add I'll suggest a 75/118 jet combo. Jets-r-us is a good source
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 nuts and bolts restore in progress


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  5. #4
    Member mikemo's Avatar
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    Thanks JT and LDR.
    I've been trying to line-up all the parts I need and was looking on Jets-R-us for the correct replacements. I noticed something strange. I think that the pilot jets that are installed in these carbs are not only the wrong jet size, but the wrong type of jet all together. As you can see this is an authentic Keihin jet, but I think it is too long. This jet measure 28mm long, and it looks like the correct pilot jet should be 23.5mm. Can someone please confirm this for me?

    Considering the jets are not only the wrong value, but the wrong size, perhaps someone tried to use a carb rebuild kit for a different carburetor? With the pilot jet 4.5mm too long, perhaps the rubber plugs didn't fit, so they tossed them?

    Looks like this carb rebuild is going to cost about 1/2 what I paid for the bike

    1982 CB450SC jet sizes-dscn0802.jpg

    Here's a closeup of the marking showing the "K star" that Keihin uses.

    1982 CB450SC jet sizes-dscn0804.jpg

  6. #5
    Super Moderator longdistancerider's Avatar
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    The Honda fiche identifies #48 in this fiche as a 99103-420-0380 or 0400. 38 is the standard size on all these but I'd switch to the 40.
    https://shop.westernhonda.com/fiche_...982&fveh=12281
    Jet-R-Us shows the 99103-420 with the measurements you list and since they are a very trusted source I'd believe them
    https://www.jetsrus.com/a_jets_by_ca...99103-420.html
    Sounds like the PO or someone working for him just threw anything that looked sort of close at these carbs.
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 nuts and bolts restore in progress


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  7. #6
    Member mikemo's Avatar
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    The folks who I bought the bike from were the original owners. I'd like to think it was the PO and not a professional mechanic who made this mess.

    My orders are placed from Honda for carb gaskets, mixture screws and float needles. Jets-R-Us for all new jets (one size up). 4-into-1 for accelerator pump and air cut valves. I had to resort to Ebay for the 61C needles.

    Here's hoping for a well-running bike when I'm done. Thanks again for the advice.
    longdistancerider likes this.

  8. #7
    Senior Member blu3fan's Avatar
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    darn. Im late to the party here.
    enjoy. https://www.z1enterprises.com/
    Their prices on some items such as carbs for these bikes are unbeatable.
    These are not Oem carb jets. but I have had an amazing experience with z1
    1982 cm450e hardtail conversion.

  9. #8
    Member mikemo's Avatar
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    Even with the stress and anxiety of an impending hurricane, I'm still excited. All my carb parts are here and I'm ready to start rebuilding. Wish me luck!

    1982 CB450SC jet sizes-dscn0808.jpg
    1982 CB450SC Nighthawk
    2 x 1988 Toyota MR2 Supercharged (one finished, one under reconstruction)
    2018 Honda Civic SI

  10. #9
    Super Moderator ancientdad's Avatar
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    Quote Originally Posted by mikemo View Post
    Even with the stress and anxiety of an impending hurricane, I'm still excited. All my carb parts are here and I'm ready to start rebuilding. Wish me luck!
    I'll wish you luck on both counts... we're about 50 miles north of you and not feeling too comfy about the hurricane either - not looking forward to spending most of a day putting my shutters up and taking down all the stuff in my yard, but I'm more concerned about my big pine trees staying upright. No flooding worries where we are, but high winds could be a big problem
    Tom

    CL450 project reboot, street legal this time
    Budget drag bike project
    CB350K1 full patina project
    Ride along at the drag strip


    running points... because I'm too old for mysteries that begin with pushing

  11. #10
    Member mikemo's Avatar
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    I got the carbs back together and back on the bike. The weather is stormy so I only just started it up in the garage for a few seconds. I'll know more tomorrow when I try to balance and adjust the mixture.

    One thing that bothered me is the springs in the vacuum piston. Can someone tell me if these look like they've been modified (cut)? Thanks!

    1982 CB450SC jet sizes-dscn0814.jpg
    1982 CB450SC Nighthawk
    2 x 1988 Toyota MR2 Supercharged (one finished, one under reconstruction)
    2018 Honda Civic SI

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