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Thread: Fine Around Town, Dies at Higher Speeds

  1. #11
    Senior Member doode's Avatar
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    How long does it take for the idle to go from 1.2 to 5k?
    How long does it stay there?
    How long does it take to slow and stall?
    When the idle climbs, what happens when you apply 3/4 choke?
    When it slows back down, what happens of you blip the throttle?
    Are you letting it idle with the cap vent open?
    Open the carb drain screw at the bottom of the bowls once it does, or Try using clear fuel lines.
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  2. #12
    Supporting Member pamcopete's Avatar
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    Fuel starvation can cause that sequence. At first, the fuel starvation causes a lean mixture, which causes a high idle, eventually there is no fuel, so the engine stops. Could be back to the plugged tank vent or some other fuel restriction. It's insidious because by the time you check for fuel in the bowls, it has replenished and the sequence then starts over again. This condition can be worse with low fuel in the tank, so try with a full tank.
    Last edited by pamcopete; 04-21-2017 at 03:44 PM.
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    Ride. Enjoy. Life is simple.

  3. #13
    Member A motorcycle nut's Avatar
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    This might be your problem
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    Danman
    1966 CB450 K0
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    http://www.amotorcyclenut.com/

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  5. #14
    Member A motorcycle nut's Avatar
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    you should also check your timing advance unit.
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    Danman
    1966 CB450 K0
    1966 305 Superhawk
    1983 CB450 SC
    http://www.amotorcyclenut.com/

  6. #15
    Member JimmyRiot's Avatar
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    Quote Originally Posted by A motorcycle nut View Post
    This might be your problem
    Quote Originally Posted by A motorcycle nut View Post
    you should also check your timing advance unit.
    THANK YOU M-Nut, I'm gonna do the hose coupling thing, and if needed I'll follow your 2nd video's advice. I "liked" your YouTube videos, --very well done! Thanks for speeding up the screwing/laborious [boring] parts, and music even! Nice video editing skills. I also subscribed to your channel (but I think I already was).

    Quote Originally Posted by pamcopete View Post
    Fuel starvation can cause that sequence. At first, the fuel starvation causes a lean mixture, which causes a high idle, eventually there is no fuel, so the engine stops. Could be back to the plugged tank vent or some other fuel restriction. It's insidious because by the time you check for fuel in the bowls, it has replenished and the sequence then starts over again. This condition can be worse with low fuel in the tank, so try with a full tank.
    Dear PamcoPete, thanks for the insightful & informative reply! I'm indeed starting to suspect the fuel supply thanks to you all. My cap vent is clear & I can practically breathe through it, but I'll try w/ full tank & open cap as I rule stuff out.

    DOODE Thank you!
    Quote Originally Posted by doode View Post
    How long does it take for the idle to go from 1.2 to 5k?
    ----These days about 4-5 minutes but I will time and film it tomorrow.
    How long does it stay there?
    ----I'd say about 1-2 minutes. Again I'll time/film it tomorrow
    How long does it take to slow and stall?
    ----It stays up there like 1-2 min then creeps down, gets lower & lower, then I nudge the throttle to keep it from dying, then it keeps going down & doesn't respond to throttle. At this point, the more I throttle, the faster it dies.
    When the idle climbs, what happens when you apply 3/4 choke?
    ---Dunno, I will try your "choke" test tomorrow
    When it slows back down, what happens of you blip the throttle?
    ----if I give it a little it'll keep it running a little longer, if I open up too much it dies. If I wanna restart I gotta have throttle open at least somewhat.
    Are you letting it idle with the cap vent open?
    ----No BUT I gotta say I have the cleanest vent-cap on the block. I can breathe through it so I don't think it's making vacuum, but it won't hurt to do the test with it open so I will.
    Open the carb drain screw at the bottom of the bowls once it does, or Try using clear fuel lines.
    I have clear lines. Open the screw when? When it does what?

    Thanks all, really. I'll take a video on my phone tomorrow of the whole process. Jimmy
    Last edited by JimmyRiot; 04-21-2017 at 10:44 PM.
    CB350K3

  7. #16
    Senior Member doode's Avatar
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    Are your carb bowl vents clear?
    Once the bike idles itself to sleep, turn off the gas and pull the fuel lines from the carb bowl. The undo the float bowl drain screw... How much gas comes out? Make sure you have something to catch or divert the gas from getting on your engine.
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  8. #17
    Member JimmyRiot's Avatar
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    I'll try that too, thanks doode.

    Since you guys really thought it was a fuel delivery thing I re-did the idle test (just letting it idle) with the gas cap open, and it didn't rev high then die! Even though I cleaned the gas cap mechanism I guess it wasn't good enough so I took it apart again and made each of the 3 air holes on the discs a little bigger, and this seems to have solved it. The idle still varies, but from 800rpm to 2k (no more racing to 5k then die). This led to an interesting discovery: As my idle was wavering I put my multimeter on the battery and noticed the stock charging system kicks in at about 1,900 - 2k rpm. I was under the impression 3k was typical, so to me this is good news.

    Question: What RPM does your charging systems kick in? I even have a modern Reg/Rec that I haven't installed yet, & now I'm in no rush because I feel pretty good about my stock system, even with their bad reputation... I also still even have the same $30 distilled water battery it came with, but I'll get around to doing all these at once w/ a yellow MotoBatt & H4 headlamp, but I want to get it running well first.

    It still doesn't like to rev above 7k when driving. It still hesitates & I don't yet feel comfortable going 55-60mph, but I'm making progress, and I still have a bunch of your tests to perform so tomorrow (today --I work nights) I'll hopefully get a little further towards my dream of going on a long motorcycle ride.

    I DID make a video, but it didn't do the high-rev then die thing (because vent problem solved) and it went on for like 25min so I didn't publish it.

    P.S. I also noticed air escaping from where my muffler meets the exhaust pipe so that can't be helping matters... I'm ordering the graphite exhaust gasket from Common Motor and a new heavy duty 1-3/4" clamp from DCC (that's the right size right?). Hopefully as I keep learning stuff I'll be a help-giver on here, not just a receiver
    Last edited by JimmyRiot; 04-23-2017 at 03:43 AM.
    CB350K3

  9. #18
    Senior Member JamesPal's Avatar
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    If you are having a fuel supply problem and the petcock is not performing, take it apart and clean it. New seals are available from Honda. There is a screen in there and it may need cleaning. You should not need to tee off the delivery tube. There are millions of 350/450 bikes that run fine in the original Hm configuration.

    I went to a lot of trouble to replace the felt seals in my carbs. The throttle shafts can be removed by drilling the peened tails off the screws and then using red thread locker when reinstalling them. What I learned was it is not the seals, they must be oiled. I decent job of oiling them can be done by removing the carbs, use duct tape to tape them to a shop vac hose, put you hand over the open end of the carb and spray liquid wrench white lithium aerosol into the seals. There is a youtube video about this.

    Make sure the engine is in a good state of tune. Make sure the valve clearances are correct and the timing is spot on. Use a timing light. +1 on the PAMCO, I have one on my 450 and it runs like a top. Don't expect it to correct a running problem. The bike should run fine on points.

    One last thing, if you are running original coils and condenser, one of these may be the culprit. The coils could be getting hot and cutting out.

    Make it run the way Honda intended, then start thinking about modifying with an electronic ignition. Many people on this site have put an electronic ignition on a bike expecting it to solve their problem and wound up disappointed. Once you get it dialed in and ride it the first time you will understand.
    JimmyRiot likes this.
    Jim Palmer
    '85 GL1200I (Garage Find)
    '81 GL1100 STD (Project)
    CB450 K5 Done
    http://www.hondatwins.net/forums/1-p...s-cb450k5.html
    What I learned from Restoring a CB450 K5
    Watch Mike and Jim Take on Mt Erie Washington State
    "If everything seems under control you are not going fast enough" Mario Andretti...

  10. #19
    Member JimmyRiot's Avatar
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    Quote Originally Posted by JamesPal View Post
    If you are having a fuel supply problem and the petcock is not performing, take it apart and clean it. New seals are available from Honda. There is a screen in there and it may need cleaning. You should not need to tee off the delivery tube. There are millions of 350/450 bikes that run fine in the original Hm configuration.

    I went to a lot of trouble to replace the felt seals in my carbs. The throttle shafts can be removed by drilling the peened tails off the screws and then using red thread locker when reinstalling them. What I learned was it is not the seals, they must be oiled. I decent job of oiling them can be done by removing the carbs, use duct tape to tape them to a shop vac hose, put you hand over the open end of the carb and spray liquid wrench white lithium aerosol into the seals. There is a youtube video about this.

    Make sure the engine is in a good state of tune. Make sure the valve clearances are correct and the timing is spot on. Use a timing light. +1 on the PAMCO, I have one on my 450 and it runs like a top. Don't expect it to correct a running problem. The bike should run fine on points.

    One last thing, if you are running original coils and condenser, one of these may be the culprit. The coils could be getting hot and cutting out.

    Make it run the way Honda intended, then start thinking about modifying with an electronic ignition. Many people on this site have put an electronic ignition on a bike expecting it to solve their problem and wound up disappointed. Once you get it dialed in and ride it the first time you will understand.
    That's great Jim, thank you - some pretty solid logic. I'll also find that video. The condensers are new but the coils are not so I'll check in to that. The petcock's nice & clean, confidant my fuel supply is all OK, no more dying, just doesn't wanna go above 7k RPM. At least now I can move on in this process of elimination. From what I've read these bikes are supposed to LOVE going up high!
    CB350K3

  11. #20
    Senior Member JamesPal's Avatar
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    Yes it should like to rev, apologies to those who have seen this video, but I love it

    Lefty, 76TWIN and JimmyRiot like this.
    Jim Palmer
    '85 GL1200I (Garage Find)
    '81 GL1100 STD (Project)
    CB450 K5 Done
    http://www.hondatwins.net/forums/1-p...s-cb450k5.html
    What I learned from Restoring a CB450 K5
    Watch Mike and Jim Take on Mt Erie Washington State
    "If everything seems under control you are not going fast enough" Mario Andretti...

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