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  1. #11
    Senior Member Rob Axel's Avatar
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    That "guitar string" didn't work for my 450.. same issue, high idle.. back the idle adjustment screws untill they no longer touch, these are the screws on the side of the carb body with the spring..(not the idle MIXTURE screws). Those plates should be closed. I this is how I can tell of one carb is getting fuel to the motor, especially on early morning startups.. with the bike running, open each carb individually by the adjustment screw lever with your fingers, if RPMs increase ur good, if not .. no fuel..,my issue was the idle jet.. tiny bit of trash. C
    I would also check for a vaccume leak, though rough/low idle is a symptom.
    Polishing the top / plungers will help..
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  2. #12
    Senior Member MechaTomato's Avatar
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    Quote Originally Posted by Rob Axel View Post
    That "guitar string" didn't work for my 450.. same issue, high idle.. back the idle adjustment screws untill they no longer touch, these are the screws on the side of the carb body with the spring..(not the idle MIXTURE screws). Those plates should be closed. I this is how I can tell of one carb is getting fuel to the motor, especially on early morning startups.. with the bike running, open each carb individually by the adjustment screw lever with your fingers, if RPMs increase ur good, if not .. no fuel..,my issue was the idle jet.. tiny bit of trash. C
    I would also check for a vaccume leak, though rough/low idle is a symptom.
    Polishing the top / plungers will help..
    If I recall correctly, when I was adjusting the idle, one side would have an effect on the rpm while the other side wouldn't. I thought they had to be "balanced" before the rpm change would take place. Guess not.
    I forget what side that was on so I'll check again, hopefully today. I also have to work out the left carb overflowing for some reason. But thanks for this info. I had replaced a couple parts with 4into1 replacedment ones, maybe they are not good.

  3. #13
    Senior Member mike in idaho's Avatar
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    Do you have some slack in the cables,when the throttle plates are closed?
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  5. #14
    Senior Member Rob Axel's Avatar
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    Each cylinder has its own separate carb.. there is no crossover or ballanxe tube. There are some real good videos on adjusting cables, sync for carbs (not balance), and one I found on making sure both butterflies are even at WOT. Unless you are REAL experienced, ballencing the carbs should be done with a monometer / gauges. But unfortunitly the 450s didn't come with ports for these tools.
    "Yes, my hands and nails have grease stains. I ride vintage!"
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  6. #15
    Supporting Member David Babbitt's Avatar
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    Everyone has their preferred method. For me, with the engine hot I remove one spark plug, get it to run on the other cylinder, then reverse the process. Knowing each cylinder can now run the engine on its own, I run them together. The idle is now too high, so I back off the throttle plate screw a little on each.

    I understand the guitar string method now, physically keeping the throttle butterfly open a minimum amount, the distance between the butterfly at the top or bottom to the carburetor wall to maintain an open venturi. I've not tried it. I know the gap is quite small as limited by the throttle butterfly stop screw.
    Last edited by David Babbitt; 04-07-2019 at 08:24 AM.

  7. #16
    Senior Member MechaTomato's Avatar
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    Thanks for all the advice.

    I ended up letting the bike warm running on both cylinders. I then took the right spark plug out and ran it on the left cylinder.

    Left side ran fine, adjusted the idle to 1100 rpm, and my idle mixture screw set on that side to highest rpm. When I took that spark plug out it was a nice brown/tan color, so the left side seems to be running just fine.

    The right side however, not running as well. I can tell that’s it’s not firing every single time. Rpm was fluctuating, and I could tell audibly that it wasn’t firing every time. I had checked the timing and it was good.

    I had taken the pilot and main jets out (while in the carb) and shot carb cleaner through before hand, and it still ran like crap

    So I’m going to take the right carb off and take a closer look. Is there anything specifically that I should look for?

  8. #17
    Senior Member MechaTomato's Avatar
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    update: I noticed that my carb was slightly crooked because the air filter is pressing up against the battery box and pushing the carb out a little. I fixed that, ran it again on the right cylinder, and sprayed with carb cleaner but there seems to have been no air leak because the problem is still there.

    I did get more time to test It though on the right side.

    What i noticed is that when it's idling, the rpm goes slightly up and down. Doesn't change on the needle, but it can be heard.
    The main part is that whenever I would give it some throttle and let it set back down, the rpm would drop way below what it was idling at.
    example: it went from idling at 1200, up to 3000 when I revved it, and dropped down to 800, and needed my throttle input to get it back at 1200, or else it would die.

    Any idea on what this could be? Clogged path on the carb to the pilot jet?

  9. #18
    Sensei 66Sprint's Avatar
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    Damaged tip of mixture screw maybe?
    "I have a mind like a steel trap.....Old and rusty, of antiquated design, and hard to get stuff back out of...."

  10. #19
    Senior Member MechaTomato's Avatar
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    Quote Originally Posted by 66Sprint View Post
    Damaged tip of mixture screw maybe?
    I checked, and compared it to the left one. The tip is not damaged. I did end up finding a leftover, dried out and broken up o ring that must not have fallen out when I did the carb rebuild.
    The new o-ring that I placed in was just kind of pressing up against it and there was a small piece that was right next to the hole that could have been making the fuel not go through right.

    I started the bike again, and it did run better, but It still wasn't running as strong as the left. It still would have that little "dip" in rpm when I gave it throttle, and there was one time were there was a pop when I blipped the throttle.

    I did my best to take out the old o-ring and visibly with a flashlight there is no old o-ring left, but maybe some bits got inside the little hole, or there is some I cannot see?

  11. #20
    Senior Member MechaTomato's Avatar
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    I took both carbs off today in an effort to try and try cleans and make it run. I spent a long time making sure all of the ports are clean on both carbs. I also checked the timing and they were both spot on.

    On the left carb (the good one), I had found that there too, had been an old o ring stuck inside the idle mixture screw, and even though it had been running fine, I took all the bits out and made sure the holes and paths were clear from that before putting the screw back in. Other than that, the left carb seemed to be in good shape from my understanding.

    On the right carb, it looks just like the left one. I had cleaned out the same idle ports, and I had removed the old stuck o ring before but I checked the passages again and they were clear.

    For both carbs I checked the float height, 20mm, used a credit card and did the wet method. I also did a quick sync with the guitar string method to set them right again

    I put both carbs back on and ran it. Started right up, but still not running quite right. The idle still was wonky. I could hear the rpm going up and down, but it's almost non existent on the rpm gauge. I can see it move up and down a little bit, but it's hard to tell because the needle kinda shakes. I let the engine sit at 3k rpm for a few minutes so it can warm up. I then ran the bike on just the right cylinder, and here is a video.



    it's hard to tell but it sounds like its not firing every time. Also, the rpm seems to drop below the idle whenever it comes back from higher rpm.

    Another note: when both cylinders were firing, the left side was super hot. Like it almost burned my hand when I touched the exhaust. The plug was black. This was like 30 seconds after starting it cold. On the right side, I could hold my hand on the exhaust. Also, feeling the exhaust pressure, I could feel the left gas to be a lot hotter than the right.

    Sorry for so much information, Im just chasing my tail with these damn carbs. the bike is so close to being up and running

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