Author Topic: 750 won't idle after reinstalling carbs  (Read 1019 times)

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Offline backburner

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750 won't idle after reinstalling carbs
« on: February 21, 2009, 03:49:42 PM »
Hello everyone,

I've had my K4 for about 5 months now.  I have been lurking on SOHC4 for most of that time and you guys have guided me through replacing the air filter, front fork seals and throttle cables.  My thanks to everyone who takes the time to post such detailed information.

I decided the cold winter months here in Nova Scotia were a great time  to pull the carbs off and replace the rubbers that run from the engine to the carbs.  I also did my first oil change since owning the bike.

When I put the bike away everything ran great and the bike idled fine.  After reinstalling the carbs and tightening up all the drain plugs the bike started up fine, revs up fast with no hesitation but it won't idle.  If I release the throttle the bike will idle for a few seconds before beginning to struggle and finally dying.

I figured it could be an air leak either between the heads and carbs or carbs and airbox.  Reinforcing this guess is that the rubber on the number one cylinder doesn't sit quite flush to the carb manifold.  I fiddled with it a bit, but couldn't get it to sit completely flat.  My other guess is that the positioning of the throttle cables is wrong, but the carbs close all the way so this shouldn't cause my problem... right?

I appreciate any insight into my idle problem

-burner

mutt

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Re: 750 won't idle after reinstalling carbs
« Reply #1 on: February 21, 2009, 04:12:14 PM »
how old is the fuel in the tank? 'modern" gas goes bad rather quickly.
Were there any cracks in the carb to head boots?
Could the idle speed screw/knob have been moved?
Is the bike not idling at completely warmed up? Or just cold?
Will it idle if you turn the speed screw/knob up a bit?


Offline backburner

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Re: 750 won't idle after reinstalling carbs
« Reply #2 on: February 21, 2009, 04:57:27 PM »
how old is the fuel in the tank? 'modern" gas goes bad rather quickly.
Were there any cracks in the carb to head boots?
Could the idle speed screw/knob have been moved?
Is the bike not idling at completely warmed up? Or just cold?
Will it idle if you turn the speed screw/knob up a bit?



Filled the tank and added stabil before parking for the winter
The carb to head boots are brand new... the #1 cylinder is out from the carb manifold by less than a mil on the bottom
Is this the idle screw or the thumb knob on the throttle?  I didn't mess with any of the carb settings, but I'm pretty sure I moved the screw on the throttle when installing new cables... I didn't really know what it was for until I did a quick search just now.
My bike never idled well cold (first minute or two of running)... should it?  I let it warm all the way up and it still wouldn't idle
My answer to question 3 probably answers this question...

mutt

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Re: 750 won't idle after reinstalling carbs
« Reply #3 on: February 22, 2009, 08:11:17 AM »
thumb knob on the throttle.....you didnt touch the idle mixture screws did you?

Offline backburner

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Re: 750 won't idle after reinstalling carbs
« Reply #4 on: February 22, 2009, 09:53:37 AM »
Only thing I did to the carbs was remove the bowls and give them a good cleaning... I didn't touch anything else.

I am going to mess around with the speed knob today... I think this might be the problem.

Offline backburner

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Re: 750 won't idle after reinstalling carbs
« Reply #5 on: February 24, 2009, 05:24:26 PM »
Mutt, it was the speed screw... I didn't realize how sensitive this thing is, I must have bumped it when I had the carbs off.  Thinking back, it seems a little obvious.

Thanks for the help.

mutt

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Re: 750 won't idle after reinstalling carbs
« Reply #6 on: February 24, 2009, 05:53:02 PM »
hey, cool man- welcome to wrenching!