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  #1  
Old 27th February 2014
jimmy the hand jimmy the hand is offline
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Default buell chop cv carb idle setting

Good evening,

Have used a xb9r 2003 motor for my build, bike starts and runs fine but when warm the revs at idle to my ear is high. I am aware that a modern motor will have an increased rpm at idle compared to an older Harley, and thus not have the classic Harley sound.

I have a 45 pilot jet in a klien cv carb, I have replaced the stock air/fuel mixing screw with an easy use type, both rubber and metal washer and spring are correctly fitted over needle. however when turning screw all the way in there is no change in rev idle, also when screw is all the way out, also no change in the revs, still revving high. this process is meant to increase (when screw out) and decrease (screw in)the revs, but nothing happens!

I ve checked for air leaks at the manifold at the carb end and head end by spaying some wd40 to see if the engine rev/tone changes, nothing so am thinking that's ok.

the idle adjuster is totally screwed out and the throttle cable is slacked out.

so not sure if there is a problem with the mixing screw or if I need to drop to a 42 or 40 pilot jet. still think there should be some change in rev/idle with a 45.

any thoughts or questions?
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  #2  
Old 5th March 2014
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Don Burton Don Burton is offline
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Yes, I have thoughts. Something isn't quite right if you have cable slack and the idle adjusting screw still won't allow you to set the idle so low that it would kill the motor. When everything is working right, there is no reason why the idle couldn't be set as low as you want to go except that it isn't good for the motor to set it lower than 1000 rpm or so due to oil circulation. You shouldn't use your idle mixture screw to try to set your idle RPM as you state that you have done and don't replace the pilot jet in an attempt to accomplish the same as you stated that you are contemplating doing. However, turning the idle mix screw in to lean it out certainly should affect your idle speed unless your throttle plate is open so far that turning the idle mixture screw has little effect. Something else is holding your throttle plate open or otherwise affecting the mixture, which is causing your idle to remain high, and you will have to look for it.
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  #3  
Old 5th March 2014
jimmy the hand jimmy the hand is offline
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Default

Thanks Don, will take the air filter of so I can see what is happening with the throttle plate. Would you say that with a warm engine you should be able to turn the idle screw out and decrease the rev a fair bit and even kill the engine? apart from the plate and a possible vac leak that I may be missing is there anything else that would increase rev at idle. Do you think running a cv carb on a xb9r engine has anything to do with it?
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  #4  
Old 5th March 2014
jimmy the hand jimmy the hand is offline
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Default

Also the increase in rpm only seems to happen when the engine is warm post short ride. When cold it sounds fine, but this maybe due to the cold engine disguising the problem.
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  #5  
Old 5th March 2014
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Quote:
Originally Posted by jimmy the hand View Post
Thanks Don, will take the air filter of so I can see what is happening with the throttle plate. Would you say that with a warm engine you should be able to turn the idle screw out and decrease the rev a fair bit and even kill the engine? apart from the plate and a possible vac leak that I may be missing is there anything else that would increase rev at idle. Do you think running a cv carb on a xb9r engine has anything to do with it?
If you turn the idle mix screw out too far it will fall out of the carb. Until that point I don't think that it will kill the engine but I have never tried it. Turning the mix screw all the way in at normal idle speed certainly ought to slow the motor down or kill it unless the screw or seat has been buggered somehow.
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  #6  
Old 5th March 2014
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Hi Dan. Is it possible that there is confusion between the mixture screw and the idle stop screw? This discussion sounds a bit disconnected somewhere.
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  #7  
Old 6th March 2014
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He seems to know the difference but he keeps going back to the topic of adjusting his idle speed with the Idle Mixture Screw or even by changing to a smaller pilot jet, which makes no sense.
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Old 6th March 2014
jimmy the hand jimmy the hand is offline
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Default

Yea do no the difference, my last post was ref the idle adjusting screw, that sets the idle not the mixture screw that adjusts the mixture of air and fuel. So the question I am asking is -

Would you say that with a warm engine you should be able to turn the idle screw out and decrease the rev a fair bit and even kill the engine? thus my idle screw is all the way out and the engine rpm are still more then enough.

Also the reason I Keep going back to the pilot jet is I would like to no if this could be a factor for increased rpm at idle, I can see the logic in why it might.
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Old 6th March 2014
jimmy the hand jimmy the hand is offline
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Also just checked the throttle slide; working fine. Have changed the throttle to a better made one. Will get some propane to double check for air leaks and when rain stops will take her for a ride and see how I go.
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Old 6th March 2014
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Don Burton Don Burton is offline
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Quote:
Originally Posted by jimmy the hand View Post
So the question I am asking is -

Would you say that with a warm engine you should be able to turn the idle screw out and decrease the rev a fair bit and even kill the engine? thus my idle screw is all the way out and the engine rpm are still more then enough.

Also the reason I Keep going back to the pilot jet is I would like to no if this could be a factor for increased rpm at idle, I can see the logic in why it might.
Can you be more specific as to which "Idle Screw" you are talking about? Are you referring to the idle mixture screw or the idle speed screw?

No, your pilot jet isn't a factor in increased rpm at idle that you can't seem to regulate. You should be able to adjust your idle speed screw so that the idle speed is so low that it isn't practical no matter what pilot jet you are running. Forget about your pilot jet for now as it isn't causing this problem. I don't know what is.
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