finally got to put some miles on, with a few issues...
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  1. #1
    Senior Member CB450MWL's Avatar
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    finally got to put some miles on, with a few issues...

    Went for a ride yesterday and put 80 miles on the 72 K5 I have been messing with. I live in Western North Carolina at about 22-24 hundred foot elevation surrounded by 3,500 ' so I went up over one mountain and back then up in the other direction and back. I checked the plugs at intervals, first check seemed a little lean and it didn't have good throttle response when the tach was jumping between 5 and 6,000 rpm so I backed the mixture screw out 1/2 turn to 2 turns out and it ran a little better. The next plug check looked a little better but still lean so I backed it out another 1/2, after that adj it seemed to have more response too. It stalled at the light when I got back due to low idle so i adj the throttle up to about 1200 rpm. It jumped out of second to neutral a couple of times and I had to adj the clutch lever a little also, I don't think that is related to each other. I really like the sound of the new exhaust which has baffles and the pipe wrap looks good and hopefully serves a purpose other than looking good. The foot brake lever has already rubbed a hole through the wrap but hoping it will hold up, it was the first time I ever wrapped an exhaust and it wasn't as easy as I thought it would be. If I have to do it again I won't buy the cheap stuff but something with a tighter weave. Any way happy with the way it's going and now I can concentrate on the way it looks which I'm not all that disappointed with just a few little things. Here is the last pic... well when I figure it out I will post one... Oh there it is in my avitar, I guess you might be able to click on it and enlarge it.
    1972 CB450 K5

  2. #2
    Senior Member ancientdad's Avatar
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    Good to hear you got to ride it, glad things are pretty much sorted out overall. Clicking the avatar only takes someone to your profile so no, we can't see the picture... and you know how we like pictures
    Tom

    Ride along at the drag strip - https://www.youtube.com/watch?v=20jFPazXlvU



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

  3. #3
    Senior Member WintrSol's Avatar
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    For starters, adjusting the mixture screw only affects the idle mixture, and at throttle settings just a bit above that. Opening it up that much is probably what caused it to stall while idling, because the engine was choking on too much fuel. Running lean above about 1/10 throttle is controlled by the jet needle position in the needle jet, up until the air flow lifts the CV piston most of the way. Since engines run generally rich at higher altitudes, you must have a really small main jet, or low-restriction air filters (or both). Back pressure from the exhaust can have some effect on the mixture, but is less important than jets and air filters.
    finally got to put some miles on, with a few issues...-carb_operation.jpg
    Rick

    Mine is a mostly 1970 CB450K3

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  5. #4
    Senior Member CB450MWL's Avatar
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    Still trying AD, I guess I'll have to find someone to help me with the photo thing. As for the bike I have the stock air boxes back on and I used a carb rebuild kit and the jets I used were the same as the ones I took out. Did all of these bikes sold over here have the same jets or did they put different ones in the ones sold at different altitudes? Where would you start with the mixture screw? I started 1 1/2 turns out and it is now 2 1/2. I think it stalled because the idle was too low or from running it at 50 -60 mph for 1/2 hr up and down the mountain might have caused the settings to change slightly? That is the first time it has been run that much in who knows how long. Any way I'll get it sorted the more I run it and learn about it, If it don't blow up that is. Just kidding but actually possible, that would suck.
    1972 CB450 K5

  6. #5
    Senior Member WintrSol's Avatar
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    The jets changed with the different carb numbers, and also changed from the K3-K4 to the K5. My parts guide shows the stock jet for the K3 is #130, while the K5 had a #140; it also shows different part number carbs for the K5, and different needle jets/jet needles, and a few other minor differences. BTW, with the exception of the needle jet/jet needle, you don't need to replace the other jets unless they are damaged, as fuel doesn't wear on the brass. The parts book lists a series of optional jets to choose from, to tune for local conditions. AFAIK, the bikes weren't sold with different jets based on local conditions, but may have been adjusted by the dealer; I suspect dealers in Denver put in smaller jets for their customers, since they are a mile high.

    To set the mixture screw, I start around the 1-1/2 position, and tweak it to jet the highest idle, per the manual. When I do, I aim the exhaust at a wall or door, so I can hear any sputtering and the pitch of the exhaust change with rpm. You can also try the rpm drop test: when fully warm, raise the rpm to about 3000, then let the throttle quickly drop back to idle. The rpm should drop smoothly and directly to the set idle. If it hangs a bit, then settles down, the screw is set too lean. If it drops below normal, then comes back, too rich. In your case, it dropped too low and stalled because it was way too rich. If I recall, mine are about 1-3/4 on one side, and barely over 1-1/2 on the other, but it has been a while.

    Have you verified the float levels? Just a little off will directly affect the mixture, too.
    Last edited by WintrSol; 03-14-2019 at 09:43 AM.
    Rick

    Mine is a mostly 1970 CB450K3

  7. #6
    Senior Member ancientdad's Avatar
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    Quote Originally Posted by CB450MWL View Post
    Still trying AD, I guess I'll have to find someone to help me with the photo thing.
    Not sure how much you know or need to know, but this is a good start if not knowing where to click is part of the problem

    finally got to put some miles on, with a few issues...-post-pics.jpg
    Tom

    Ride along at the drag strip - https://www.youtube.com/watch?v=20jFPazXlvU



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

  8. #7
    Senior Member CB450MWL's Avatar
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    Let me see here
    finally got to put some miles on, with a few issues...-img_20190308_114751-1-.jpg
    I went to a local muffler shop and had him make 8" extensions and welded them to the stock header pipes, then wrapped them and mounted the new mufflers. Also had to make support brackets. WintrSol thanks for the suggestions and I will concentrate on the carb. You sound like you know your way around these carbs well, this is my first so there is a learning curve. Would you mind if I PMed you questions as I go along? Having a few days of rain but when it clears up I will take it out again.
    Last edited by CB450MWL; 03-14-2019 at 08:49 PM.
    1972 CB450 K5

  9. #8
    Senior Member WintrSol's Avatar
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    I know something about carbs, as do a number of the other members here. Feel free to ask questions of any of us. PMs are OK, but putting it out here may help the next guy, too.

    BTW, how far from Deal's Gap are you?
    Rick

    Mine is a mostly 1970 CB450K3

  10. #9
    Senior Member CB450MWL's Avatar
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    Deals gap or the Dragon as they like to call it here is about a 45 min. ride. Great riding and many twisting mountain roads around here.
    1972 CB450 K5

  11. #10
    Senior Member WintrSol's Avatar
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    Quote Originally Posted by CB450MWL View Post
    Deals gap or the Dragon as they like to call it here is about a 45 min. ride. Great riding and many twisting mountain roads around here.
    That's for sure; we usually camp at the Iron Horse for a week nearly every summer, and get fuel at a no-ethanol station at the intersection of 143 and 129, or at the turn off to go into Bryson City from the south. These old bikes really prefer real gas.
    Rick

    Mine is a mostly 1970 CB450K3

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