what's that screw for anyway??? carburetor - idle screw

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blacklabel7345

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...when i first got mine, i also thought it was for mixture, a closer look before install and i would've known better.

funny thing, tho:

when i thought it was a mixture screw, it behaved like one. then i learned it was for adjusting idle, now that's what it does :LOL:

maybe i've got the magic carb....

lol...did u get it from the chinese dude in "the gremlins" ?
 
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Scottm

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Now is it my imagination too? Until my Happy Times motors seemed to reach the break-in stage, the idle screw seemed useless. Now that my new motor has over 100 miles on it, the screw seems to have more of an effect and I can set it right.
While letting the motor warm up, I fool around getting stuff ready for a ride. When the engine starts running higher I'll back out the screw until it idles smooth again. I may repeat this process several times until it had been warming up for 5 minutes or more. I don't have to do that on my other bike that has broken in.
 
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mnbiker

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I didnt read all the posts but one of the first few said that with the idle out 5 turns the motor had power but at 4 none. Set the idle to best sounding performance, there has to be some other adjustment to adjust high speed running, if not i recomend a different carb.
 
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Egor

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I don't like the stock carb, the one with the one Idle speed adj. I am only using it on one engine, but I have a little trick. I take it apart and drill a .050 hole from the float area into the venturi just as close as I can get to the engine side of the runner. There is no provision for idle mixture so this gives something instead of flooding the mid range to get an idle. I have a real carb to install but not yet. I have two water pimps that have the crude carb's on them, they work fine because they are not intended to idle. If you get the new style carb, you will love it and never go back. Have fun, Dave
 
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Mogyver69

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Hi Everyone, Great toppic you got going here. I just put together our first install on a 21 speed mountain bike. I was in another toppic page earlier in the week and there are many of you that were at that page so you maybe familiar with my situation alittle. Anyway getting right to the point. I originally had a no start , after spending alittle time diagnosing I discovered I was sleeping on the job and wired my kill switch wrong. Today finally I pulled her out for the first time and got her started up. I had to choke her up 3/4 choke to keep her runining. I removed the carb needle as you guys were discusing prier to reading this thread to see if that screw was a mixture screw as youve been talking about or a idle screw. Because I wasnt getting any richer of a condition when turning the screw but my idle was increasing when Id turn the screw in. It is definetly 100% a idle screw. At least on my Carb. I have a NT carb. I put it all back together and fired her back up set the idle and drove her around but I have to leave the choke closed 3/4 for her to run. Its obvious I have a lean condition. I was thinking vacumn leak obviously first off but I did want to check with you guys here and see if this was something you guys have seen on a regular basis and if this was something where I just needed to richen the carb with the techniques youve been talking about in the last couple posts. Thanks guys.
 
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mnbiker

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i dont know the carbs yet as i am new. Do you have a slide as your throttle? If so i have seen discs you adjust for your throttle to open up more meaning more air so you can unchoke your bike. if its like this and you try it remember your idle will be going up.
 
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Mogyver69

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i dont know the carbs yet as i am new. Do you have a slide as your throttle? If so i have seen discs you adjust for your throttle to open up more meaning more air so you can unchoke your bike. if its like this and you try it remember your idle will be going up.

Im not sure what you mean by a slide nor do I understand about opening my throttle more helping me with my lean condition. Raising your idle by opening your throttle isnt going to help me with a lean condition.

Anyway, Ive sealed my intake to carb space and changed the setting on the needle valve to richen the mixture. Will try it this afternoon and see if that helps. Thanks for your input.
 

Pablo

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Adjusting the mixture is pretty easy. Unscrew the cap on top of the carb where the cable goes in. Pay attention to what it looks like when you are taking it apart. The washer with the slot in it goes OVER the E-clip when you reassemble it. ....... Top groove = lean. Bottom groove = rich.

Help - my bike is suffering.....it's running extremely rich even with the E-clip in the top groove. My Chinese instructions pictorially show the slotted washer UNDER the E-clip. Blaze says OVER the E-clip.

Which way is correct?

BTW excellent post Blaze.
 

srdavo

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Help - my bike is suffering.....it's running extremely rich even with the E-clip in the top groove. My Chinese instructions pictorially show the slotted washer UNDER the E-clip. Blaze says OVER the E-clip.

Which way is correct?

the slotted washer has to be on top of the e-clip...this allows the spring to push the needle/slide back down.

my instructions showed wrong too!!
 
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mickey

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the slotted washer has to be on top of the e-clip...this allows the spring to push the needle/slide back down.

I agree. That could be the whole problem right there. With nothing to hold the pin down, it would probably push up. It would be like running the clip way below the bottom slot.
 
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