Bike starts but dies - new build
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Thread: Bike starts but dies - new build

  1. #1
    Senior Member Crashoverride's Avatar
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    Bike starts but dies - new build

    So after cleaning and rebuilding my carbs I got the bike to start today Now it only runs for about 30 seconds so I need help tuning it.

    This is what I noticed so far.

    1. Both bowls were getting gas.
    2. Carbs were benchmark synced.
    3. I can get it to start but it runs for about 10-20 seconds and then dies. It will fire back up and do about the same each time.
    4. I am getting exhuast out of both pipes but only one seems to be getting warm.
    5. Idle screw tried 1 , 1.5 and 2 out.

    Where do I go from here?

    https://goo.gl/photos/QfcZM81GoZ3okfgP7
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  2. #2
    Senior Member LiamG6's Avatar
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    Running on one cylinder? Check the spark of the cylinder that doesn't get warm exhaust. If it has spark and the timing is correct then check the carb again. If no spark check points gap and timing, if still no spark get new spark plug and check coil and HT leads and plug caps.

    Have you done a compression test? Have you had the engine or top end apart?

    EDIT: I looked at your build thread and watched the video of the bike running, seems to purr pretty sweetly then die, are the float heights in the carbs set right?
    Last edited by LiamG6; 05-20-2017 at 06:39 AM.

  3. #3
    Senior Member dtsmjr8dan's Avatar
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    Add to above.....Valve lash seems a bit much in video. Double check your valve clearances...you may also have one too tight.
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  5. #4
    Senior Member Crashoverride's Avatar
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    Ok so this morning I checked the valves which seem spot on again. I pulled the left cap up 2 notches on the spark plug (have to push down again to see if that really made any diff) I removed the cap over the points because I read it might be arcing or grounding to it. (Have to test with it back on) I then reset the idle with the directions below. It fired up on both, pipes got hot pretty quick and I was able to give it throttle and engage the other jets. Both are really firing now and it could of idled but my left carb over flow was just pissing gas while it was running, like not a drop just shooting out.

    I set the float heights at 20mm, I guess that does not work - what should I set them too? The Left carb I think is a gen 3 because of the look and it uses the modern idle jet with the narrow bit washer and o ring. The right carb appears to be gen 2 as the idle screw is fatter and doesnt appear to use a washer or O ring.

    Thanks

    Carbs that have split throttle cables need to have the throttle butterflies in sync by making sure they open at the same time. This can be done with the engine off by loosening the IDLE screws completely, then with ONE hand on the throttle lever on one carb and EYES on the other slowly roll the throttle grip back. WATCH and FEEL for exact movement. Adjust sides until the both move at the same time. It's tough and will take practice to get right.

    Once you have the throttles SYNCED, then slowly turn the idle screws down an even amount. Once both touch the stops screw in 1-2 turns evenly. Start bike, warm it up and then set the IDLES, making sure they are both even.

    Once you have an idle, start working on PILOT mixture screws. Run ONE side all the way in SOFT touch and then back out 1 -2 turns. NOW turn IN and OUT and adjust for FASTEST idle. Do the same for the other side.

    NOW go back and adjust the IDLE screws for correct IDLE. With any luck and about 3 tries you will have your issues
    Bike Build http://www.hondatwins.net/forums/1-p...rst-timer.html

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  6. #5
    Super Moderator outobie's Avatar
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    what model carbs do you have? read the numbers on the side of each carb.

    350A?
    D?
    722a?

    you must use the correct float height for that model carb there are different setting for each.

    your synch instructions above are correct. it usually takes a few tries to get correct.
    For the idle mixture adjustment and final idle settings, the bike must be fully warmed up. after you get your settings close, ride the bike for 5 to 10 miles to get it to full operating temperature and do a final tuning.

    fuel overflow issue needs to be fixed before final tuning. common causes are:
    overflow brass pipe split
    fuel inlet valve leaking past oring
    fuel inlet valve needle dirty or worn
    float height wrong
    floats damaged or leaking
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  7. #6
    Senior Member ancientdad's Avatar
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    Quote Originally Posted by Crashoverride View Post
    Ok so this morning I checked the valves which seem spot on again.
    Crash - I completely agree with Dan, your valves adjustments don't sound right. Way too much ticking and - not to be critical of your efforts - if there are one or two that are too loose, there could be one too tight as well. Might not make a difference for now in low-speed running if only slightly snug (zero lash) but with extended running, it will cause a burnt valve if left that way. If things still check out correctly on the proper stroke, then it could be worn rockers and/or cam lobes causing misreads on the adjustments.

  8. #7
    Senior Member Crashoverride's Avatar
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    That video only had one side running so it may not have sounded right. I have checked the valves twice and the correct feeler gauge just go through so they are a bit loose if anything over being tight. Should I tighten them up?

    One of the carbs says JC 3D and the other says 722a KC on the side.

    I have the carbs off again to do adjustments.
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  9. #8
    Senior Member ancientdad's Avatar
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    Quote Originally Posted by Crashoverride View Post
    That video only had one side running so it may not have sounded right. I have checked the valves twice and the correct feeler gauge just go through so they are a bit loose if anything over being tight. Should I tighten them up?

    One of the carbs says JC 3D and the other says 722a KC on the side.

    I have the carbs off again to do adjustments.
    Well, all we have to go on is the sound and believe me, when you've heard loose valve adjustments over the years as often as the many guys here have and they point it out, it's likely there's some truth to it. Whether or not you can get them quieter remains to be seen (without having them too tight, of course) but it might be an indicator of some wear in the valve train that you wouldn't be aware of since you didn't pull the engine down. I don't know how much experience you have using feeler gauges (no offense intended, of course) so that's another unknown quantity for me (as well as the others too, I'm sure) but if there's excess wear on the rocker arms then it might not be something that can be completely adjusted out. Only a disassembly would fully reveal it.

  10. #9
    Senior Member Crashoverride's Avatar
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    I will adjust them slightly tighter and see. I thought they normally like to tighten up so looser was better, but its not a big job to do them again.

    Looking at my carbs I think the float valve needs to be 26mm so once that is done and the valves I will take another video for feedback.
    ancientdad likes this.
    Bike Build http://www.hondatwins.net/forums/1-p...rst-timer.html

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  11. #10
    Super Moderator outobie's Avatar
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    Yes both 3D and 722a floats must be set to 26mm

    i don't disagree about your valves but don't think that is your main issue

    are the hash marks on the valve adjusters pointing out like they should?... Pics would help
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