I am going back into the carbs again...
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Thread: I am going back into the carbs again...

  1. #1
    Senior Member CB450MWL's Avatar
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    I am going back into the carbs again...

    The bike has been running quite well last few times out with only minor issues that I think are carb related. I have the original jets and ran into a friend that works at a boat shop and he has access to an ultra sonic parts cleaner. He said he would be glad to take my carb bodies and jets and clean them for me so I am going that route soon. Does anyone here have experience with changing jets because of elevation change? The bike had 145's in it and I put in the aftermarket 150's. It came from a close to sea level area and most of my riding is done from about 2,500' to 4,500' elevation. The last time out I was going up a long 7% grade and I didn't have much throttle response. Seems I've heard that higher elevations you should or could use one size or so smaller main jets. Do you think it would run better up here with the 145's or possibly even go with some 140's. The plugs have a nice brown color on the electrodes but black and sooty around the base. There has also been a sort of stutter while trying to hold a steady 3-4,000 rpm. Thanks in advance
    1972 CB450 K5

  2. #2
    Senior Member WintrSol's Avatar
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    You should go leaner; at least, try the 145 and fresh plugs. With unleaded fuel, the insulator should not be brown, but closer to white. The stutter could be the really rich mixture, or a somewhat out of sync condition (or some of both).
    Rick

    Mine is a mostly 1970 CB450K3

  3. #3
    Sensei 66Sprint's Avatar
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    Before we can give advice on jet size, What is the setting number on your carbs? (14H, 751A, What?).......

    We CAN tell you the aftermarket brass is likely crap.....Clean and reinstall ALL original brass......

    Feel free to phone.....
    WintrSol likes this.
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."
    Contact info: E-mail; [email protected] Phone; 540-525-5199

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  5. #4
    Senior Member CB450MWL's Avatar
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    The carb is a 723A. I'll stick with the plan of cleaning the original jets and carb body, double check the float level. I watched a video on syncing the carbs, I have never done that but it looked pretty easy. The only way I set it up last time was from a video were I put a guitar string under the butterfly and used it as a feeler gauge of sorts and adjusted the throttle screw till the guitar string just slipped out. I started out with the air mix screw 1 1/4 out I think it is closer to 1 turn out right now. At first the right throttle cable was opening before the left but are both the same now. If I get stuck on something I will get back to this thread and I will update how it winds up anyway.
    1972 CB450 K5

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