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Author Topic: Engine Idle 4000 RPM  (Read 1214 times)

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Offline FeralBoy

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Engine Idle 4000 RPM
« on: July 07, 2013, 09:47:11 AM »
SOHCers,

I just finished a cosmetic rebuild of my bike (i.e. I did not touch the engine which was running fine before I started the rebuild).  During the rebuild I replaced the ignition control (which got me into the throttle control) and the four airpods with a stock airbox, and a 4 into 1 exhaust with stock 4 into 4.  I just started the bike for the first time and it immediately jumps to about 3800 RPM for the idle.  I have adjusted the gas / oil mixture but it's not really changed the idle much.  I also adjusted the throttle tension, but that did not seem to do much either.  Any thoughts on what I should look at next?

Thanks.
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1971 CB750 K1

Offline LesterPiglet

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Re: Engine Idle 4000 RPM
« Reply #1 on: July 07, 2013, 09:50:43 AM »
What bike? Have you adjusted the idle screw? The big knurled one on the carbs.
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Offline Bootlegger56

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Re: Engine Idle 4000 RPM
« Reply #2 on: July 07, 2013, 09:54:07 AM »
Did you pull the carbs during the cosmetic rebuild?
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Offline FeralBoy

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Re: Engine Idle 4000 RPM
« Reply #3 on: July 07, 2013, 09:56:57 AM »
Sorry, CB750K1 (1971).  Is the idle adjustment screw the little screw at the top or the big screw at the bottom (see picture).  If it's the bottom one, what does the top one do?  If you are adjusting the bottom screw, is there a method to follow?

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Offline FeralBoy

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Re: Engine Idle 4000 RPM
« Reply #4 on: July 07, 2013, 09:58:25 AM »
No, I did not pull the carbs.  The bike had been professionally tuned up in December and was running well.  I was just returning it more to stock and was intentionally avoiding the engine components since that's not my strong point. 
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Offline Bootlegger56

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Re: Engine Idle 4000 RPM
« Reply #5 on: July 07, 2013, 10:08:22 AM »
No the idle screw is the big knurled slotted knob on a K5 ( I believe the same on K1) in between carbs 1 and 2.  The head points downward and rests against the throttle control rail to regulate idle speed.  What you have pictured is the idle air adjustment screw.
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Ya can travel near or ya can travel far; but no matter where ya go thar ya are!

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Offline Gordon

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Re: Engine Idle 4000 RPM
« Reply #6 on: July 07, 2013, 10:55:49 AM »
Quote from: FeralBoy on July 07, 2013, 09:58:25 AM
No, I did not pull the carbs.  The bike had been professionally tuned up in December and was running well.  I was just returning it more to stock and was intentionally avoiding the engine components since that's not my strong point.

If the carbs were altered to run with pod filters and a 4-1 exhaust, then you'll need to put them back to stock for the engine to run correctly with stock components. 
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Offline FeralBoy

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Re: Engine Idle 4000 RPM
« Reply #7 on: July 07, 2013, 07:27:30 PM »
Gordon,

Thanks for the comment.  I figured that would be the case, so I may have to tackle that next, but for now I was just trying to figure out the idling.  I did find the idle set screw that Lester mentioned and I have it idling now correctly (between 1500 and 1800 RPM), so that's progress.  Thanks to everybody for their feedback and help
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Offline Tews19

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Re: Engine Idle 4000 RPM
« Reply #8 on: July 07, 2013, 07:48:12 PM »
Feral

it is important to adjust the Isle when the bike is warmed up. If not you will be racing and chasing it if cold.
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Offline FeralBoy

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Re: Engine Idle 4000 RPM
« Reply #9 on: July 07, 2013, 09:01:35 PM »
Thanks Tews.  I will warm the bike up and then check and adjust the idle. 
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