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CV Carb Idle Setup question

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Old Oct 4, 2021 | 12:24 PM
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Default CV Carb Idle Setup question
I need some help with the basics. Evo touring - standard 80 ci setup with ev27 cam. Currently trying to get the CV carb dialed in - has a 45 pilot and idle mix screw(screw under carb) 3.5 turns out. The idle air screw (the thing that pushes the throttle plate slightly open) is almost at the max of its travel pushing the throttle plate slightly open. If i undo this idle air screw such that the throttle plate closes all the way then the bike wont stay running without the choke - no matter how many turns of the idle mix screw you turn out. In the carb passage way i see like one hole which the idle mix screw directly controls and then behind that about 3-4 small clustered holes that are covered by the throttle place. No matter what i set the idle mix screw at, i cannot keep the bike running without the idle air screw pushing the throttle plate at least slightly open. Should the bike be able to idle with the throttle plate completely closed ?
 
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Old Oct 4, 2021 | 01:12 PM
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The throttle plate needs to be opened some to get fuel and air to idle, what does the engine sound like when to give it throttle, pop, surge or smooth?
 
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Old Oct 4, 2021 | 01:21 PM
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You have cleaned the carb and made sure none of the jets or passages are plugged? in your case make sure the idle air mixture and slow jet are clear
 
Last edited by mike131; Oct 4, 2021 at 01:27 PM.
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Old Oct 4, 2021 | 01:24 PM
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Adjusting idle air mixture screw http://www.harley-performance.com/ha...arburetor.html you have to make sure thats adjusted properly
 
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Old Oct 4, 2021 | 01:29 PM
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The idle adjuster screw is what is used to set the throttle plate position in order for the engine to idle.

The idle mixture screw is underneath the carb.

The idle screw must be holding the throttle plate partially open to idle, no reason to back it off.

Set the idle using the idle adjuster screw.

Go through the adjustment procedure for the idle mixture screw.

Finish by setting the idle screw so that the engine idles at the proper speed 900 RPM.

I just did this job not 20 minutes ago on my Evo (EV27 cam).


 
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Old Oct 4, 2021 | 02:28 PM
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Originally Posted by mike131
Adjusting idle air mixture screw http://www.harley-performance.com/ha...arburetor.html you have to make sure thats adjusted properly
Yeah i had read that but will give it a quick once over. One of the lines on that page that was confusing to me was "If the engine will not idle on its own during this procedure, adjust the idle set screw on the throttle side of the carburetor until it idles correctly. Now turn the mixture screw outwards (counter-clockwise) until the engine begins to run smoothly, then add 1/8 of a turn " Lol what is the difference between "correctly" and "smoothly". Do you adjust the idle air screw just enough to make the engine barely idle and then use the idle mix screw to get it to run smooth ? When i adjusted my idle air screw to let it idle correctly (around 1k rpm) , turning the idle mix screw had no effect on the idle (sorry should have mentioned that this is problem i am really chasing). Also no intake leaks.
 
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Old Oct 4, 2021 | 03:20 PM
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Actually I will warm up the bike then set the idle screw for throttle plate down around 800 rpm, so you can really hear the difference when adjusting the idle mixture screw under the carb, turn in screw idle mixture screw under carb until engine starts to run rough, then turn out until engine runs rough, turn back in half way between the two points then the idle mixture is set, then adjust your idle screw for throttle plate to idle at 1000 rpm
 
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Old Oct 4, 2021 | 03:39 PM
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If there is no change in idle when adjusting the idle mixture, I would normally say the slow jet is to large, but you have 45, so thats good, there could be something wrong with the idle mixture jet it self or its packing, turning the idle mixture screw in should cut off the fuel at idle so the carb might be allowing fuel in from an other placed it shouldn't be
 
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Old Oct 4, 2021 | 04:18 PM
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Originally Posted by mike131
Actually I will warm up the bike then set the idle screw for throttle plate down around 800 rpm, so you can really hear the difference when adjusting the idle mixture screw under the carb, turn in screw idle mixture screw under carb until engine starts to run rough, then turn out until engine runs rough, turn back in half way between the two points then the idle mixture is set, then adjust your idle screw for throttle plate to idle at 1000 rpm
Will try this. Is there a specific turn setting for idle mix screw to start with? Maybe set it at 1-3/4 to 2 turns?
 
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Old Oct 4, 2021 | 04:19 PM
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Start out rich, so 3 to 3 1/2 turns out
 
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