CB450 apparently running rich on right side only
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  1. #1
    Junior Member kettles's Avatar
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    CB450 apparently running rich on right side only

    Backstory on motorcycle. 1973 CB450, In the last 2 years I have replaced or rebuilt most of the stuff on it that makes it go (it was very neglected and had been sitting for 25 years when i got it). Pulled engine, took the top end apart and had cylinders bored .5mm over and the valves done, then I re-assembled with new pistons and rings. Replaced the points, condensers, coils, plugs, wires. Replaced voltage regulator and rectifier (with all in one unit). Starter delete. Repaired holes in gas tank, cleaned the rust out of the inside. New brake lines, brake pads, shoes, rebuild caliper, rebuild master cylinder, new chain, LED head and tail lights, new tires, rear shocks, fork seals, seat cover etc. etc. etc. Cleaned both carbs, then fully rebuilt the left and replaced and cleaned and rebuilt the right (723A Keihin Carbs). 150/38 jets in it. Factory air filter setup.

    So when i bought the bike it didnt run, and the starter was bad. I was looking for a smallish bike with kick start to setup with knobby tires and ride on trails/gravel, commute, whatever. I toiled with it and got it running drove it for a bit as is but it never ran all that great, and would die randomly and abruptly when idling. The right side had less exhaust pressure (putting hand in front of the pipe) and the plug was always more fouled.

    I have a sick problem of loving old bikes and cars, loving working on them, taking them apart, etc. but simultaneously hating it when they aren't together and running, and all the old car/bike problems. Eventually I decided to pull the engine (which was good, there was evidence of rust in the cylinders from sitting which was hurting compression). I did all the above work, more or less, after I pulled the engine. Since its been back together and running it still doesn't seem to run right. It doesn't want any choke to start it, when its stone cold it takes 5-6 kicks to get it to start, and it starts really slow and then warms up (hot, or warm it usually just takes 1 kick). It will idle till the cows come home right now (with the idle set around 1200 RPM), and will idle fine with the screws a little more closed around 7-800 but will randomly and abruptly die when idling at that speed once the bike is good and hot (FWIW, I haven't really tested this since I pulled the carbs off yesterday and cleaned them, again, and re-jetted from 145 to 150).

    Also there is a noticeable lack of power below 3000 RPM, and then it surges up as it passes 2500-3500. This is worse if it has been idling for 10-15 seconds first, and worse when hot than cold. I can blip the throttle a few times and rev it up, let it fall back down and then take off from a stop much easier than just trying to roll on the throttle and clutch without revving it first. (To be fair there isn't a lot of slip in the clutch travel either, that doesnt help).

    Lastly, at WOT, or near it anyway under load it doesn't run consistently and will sputter and miss as you rev up. It almost seems hard to get to 9K RPM under load (which I dont need to get to cuz the bike is pretty loud, but I want to be able to...)

    I pulled the plugs when I got home today and the left side fairly pristine and the right is sooty
    CB450 apparently running rich on right side only-20190710_194530.jpg

    Now, other than poking at things and reading on the internet, I don't have a lot of experience tuning carburetors, much less CV ones. I usually can turn screws one way or the other and make something run OK but I would say I am far from really knowing what Im doing and what needs to be done. So thats where I am. I dont know where to go next. I am pretty sure the float levels are the same. They looked about the same yesterday (casual observance) and I have had this bike at a shop (Retro Wrench) this winter since it was bothering me and they are the ones that replaced the floats and set the levels (one of the old floats leaked apparently).

    I want to clarify that I know the carbs are not balanced perfectly, the right side is open a little more than the left at idle. I haven't messed with it in a while but it seemed like it didn't idle as well with both throttle plates in exactly the same spot. I have not checked the boots for leaks with carb cleaner or something while it is running (which I only just thought of today). But I am looking for advice on what I should inspect/test next.

    Edit, Bike photo for motivation
    CB450 apparently running rich on right side only-20190710_194002.jpg
    Last edited by kettles; 07-10-2019 at 07:59 PM. Reason: Added bike photo

  2. #2
    Senior Member TOOLS1's Avatar
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    It sounds like a vacuum leak on the right-hand side to me. I am not real familiar with the 450s but I would suspect the throttle shaft seal and the little O-ring on the pilot screw. Or, did you rebuild the carbs with an aftermarket kit and replace the pilot screw with one from the kit? I have had them cause problems like you are describing, sooty plug and all.
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  3. #3
    Junior Member kettles's Avatar
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    Thanks for the suggestion on leaks. The carb rebuild was done using a parts kit from 4int1, https://4into1.com/carburetor-rebuil...450-1972-1974/

    Well I got it running after work and let it idle for 5-10 minutes, Then checked various spots with a IR thermometer, and the right side was running 10°F hotter at the head fins, and 50° hotter on the exhaust pipe at the head.

    Then I played with the settings. The pilot screws (are they air or fuel screws on these carbs) were just under 2 turns out on the right and just over 2 turns out on the left. I knew the right carb plate was open a little extra so i balanced it some just as a guess, and then lowered the idle down to about 1000rpm.

    Then i tried carb cleaner for leaks. A small spritz at either throttle shaft will cause the bike to die. And a spray on top of the left boot to head connection will cause it to slow down.

    https://photos.app.goo.gl/oJAz5yG8vh2K68n79

    https://photos.app.goo.gl/EmdK11FuqQoVwrw78

    https://photos.app.goo.gl/b8vjc6P6k6PEHz9f8

    That doesn't explain it to me, but its at least a start of things to mess with.

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  5. #4
    Senior Member HondaPete89's Avatar
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    Your carbs are out of whack. With 450s this can cause a big headache. Fortunately this problem is COMMON and can be solved with careful and methodical research and screw turning.
    If you have all your original carb parts in good condition, return them to your carbs, they are better quality than the rebuilt kit.
    Bench sync your carbs, sync your throttle cables, get an idle around 1.2k with equal turns on your idle screws (vertical screws on sides of carbs) then turn your air mix (horizontal screw recessed in carb body) until you hit highest rpm. Then adjust your idle screws to get back down to 1-1.2k
    Of course your carbs need to be spotless and floats correct for this to work. Do a search on this here forum and you will find excellent in-depth descriptions of the process mentioned above. Good luck.
    1975 500T
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  6. #5
    Senior Member TOOLS1's Avatar
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    Wherever you sprayed the carb cleaner and it changed RPM/died you have a vacuum leak that needs to be sealed. No amount of screw turning will make it run any better until the leaks are fixed.
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  7. #6
    Junior Member kettles's Avatar
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    Thanks again for the help.

    The factory felt seals on the shafts didnt looks like they were doing anything anymore. I pieced together a functioning seal configuration using some o-rings that will work better than what was there. When I pulled the manifold/boots off I didnt think there was a gasket at all until i realized it had become one with the boot. This has been remedied, and i had new gaskets which i also applied some hi-temp RTV as insurance. This is currently curing, ill let you know how it runs when I put the carbs back on. I would have had it back together but most of the day was spent at CC Powersports who had Jason Britton put on a show and that was a lot of fun to watch.

    CB450 apparently running rich on right side only-20190712_203225.jpg
    CB450 apparently running rich on right side only-20190712_204624.jpg
    CB450 apparently running rich on right side only-20190712_210100.jpg
    CB450 apparently running rich on right side only-screenshot_20190713-144746_photos.jpg

  8. #7
    Junior Member kettles's Avatar
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    OK. Carbs on, got the idle set up. Right side still has noticeably more exhaust pressure and more noise from that side. Right side still running a good bit hotter than the left. I checked for vacuum leaks with carb cleaner again and didnt find anything unless i let some of the spray near the carb opening (which caused it to slow). The shaft seals and such seem to work.

    CB450 apparently running rich on right side only-20190713_213439.jpgCB450 apparently running rich on right side only-20190713_213446.jpg

    I pulled the plugs, but I hadn't cleaned them since I checked for leaks the other day so i dont know how dirty stuff is from that
    CB450 apparently running rich on right side only-20190713_214331.jpg

    FYI I have a main jet assortment in the mail because all I have is 145's (installed) and 150's.
    Last edited by kettles; 07-13-2019 at 07:57 PM.

  9. #8
    Junior Member kettles's Avatar
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    Wire wheeled and carb cleanered the plugs since I dont have new ones
    CB450 apparently running rich on right side only-20190714_103155.jpg
    Re-installed and ran the bike for 10 minutes or so (on the stand). I played with the balancing, idle and pilot screws a bit more an got the exhaust pressure much closer to eachother than they were yesterday (just feeling with hand). Still a different exhaust impulse feel though. It felt fairly perky revving and whatnot on the stand.
    CB450 apparently running rich on right side only-20190714_104908.jpg
    After running the plugs weren't sooty so thats a good sign, but since they are used I can't tell rich/lean by the insulator color. Checking the exhaust pipe temps, the left side is still 50ish degrees cooler than the right?

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