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I have an 82 Honda 450 Nighthawk motorcycle that I'm rebuilding and I need to tune/balance the carbs. I have them bench-balanced and reset the idle screw on both. Now it runs a lot better, but every 10-15 seconds the idle raises and it starts sputtering out the carbs.

I assume this is just a lean mix, but could it also be vacuum or something? I don't want to tune the carbs just to realize that I need to fix something else and tune them all over again.

  • Nope, that question is more about why a cold engine has to run faster than a warm one. – Eric Fossum Jun 27 '15 at 23:06
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    @EricFossum - Do you still have this issue? If not and you have solved it, could you please populate the answer to the problem, it would be good for the site. If you are, can you share any additional troubleshooting measures? Regarding a solution, Could you please respond with make/model/year so a more defined solution can be shared with you once we figure it out? Thanks – DucatiKiller Dec 12 '15 at 3:07
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    The easiest way to tell is by trying this. Ride the bike with the throttle raised for about 100 meters, then, hold the clutch in and close the throttle so as to let the bike coast. If the the engine speed does not begin to drop immediately, you have a lean mixture. This is a definite give away of a lean engine but the lack of this sign does not eliminate the possibility of a lean engine. – krthkskmr Feb 22 '16 at 8:13
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    How are the carb boots? Any cracks that could periodically let air in and lean out the mixture? – Mysterfxit Mar 1 '16 at 5:07

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