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

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pianoman8t8

Guest
ok, so i got the engine kit from dax. Is there a way to adjust the carb., because from what i see, there is only the "idle adjusting screw" (or that's what it seems to be), and something that seems to be like a primer pump thingy??? and there is also a hole next to the air intake underneath the air filter. I took apart the carb, and there is a float with an arm extended to it, like a close off valve that goes to the fuel inlet, and there is a hole that connects to the other hole that comes out underneath the air filter....does that serve any purpose? but I see other people saying they adjust some screw to get it running right?? what screw are they talking about? or maybe it's the same one as the idler screw??? please tell me if you know anything about these carbs...
 


C

cyclemotors

Guest
Hello pianoman,

the only adjustment screw that im aware of is the one your talking about.. Factory and manual state it should be turned 4 half turns anticlockwise from fully closed..

But in my experience with every setup you will need to adjust this slightly to get the correct mixture.

I usually listen to the engine while turning the screw untill it sounds just about right when idling.
 

Tom

Active Member
Joined
Aug 4, 2006
Messages
1,064
I think thats the idle screw. To adjust the mixture, you have to pull out the pin in the carb and adjust the floater thingy to the correct pin setting (there are 4 of them). Hard to explain, I know someone posted pictures before, might want to try a search.
 

srdavo

Active Member
Joined
Nov 4, 2006
Messages
3,134
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Misinformation!!!!!

this is copied directly from my grubee instructions:

"Note: The air/fuel mixture screw should be preset at about 3.5 turns counter clockwise from the totally closed position.
*NOTE: Do not back-off screw more than 4.5 turns or vibration may loosen the screw and cause it to fall out."

I agree that 3 & 1/2 turns is not set in stone.

Another idle adjustment I've found is the cable adjuster on top of the carb. any ideas guys?

Dave
 
S

Steve

Guest
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I don't even pretend to know why, but if I set my idle screw at around 4 turns out, the engine has no power at wide open throttle. However, if I turn it out to 5 turns, the engine makes good power at wide open throttle. :???:
 
T

tirebiter

Guest
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Steve said:
I don't even pretend to know why, but if I set my idle screw at around 4 turns out, the engine has no power at wide open throttle. However, if I turn it out to 5 turns, the engine makes good power at wide open throttle. :???:
That's wierd Steve. All the idle screw does is stops the slide as it goes down into the throat of the carb. It hits a slanted slot so that screwing it in or out lets the slide stop up or down a little. As soon as you give it any throttle above idle it doesn't do anything.

Maybe you've got one of those secret carbs that the oil companies bought the patents to. :eek:
 
B

Blaze

Guest
You have the same carb I do, and I know how to adjust it.

Different manufacturers have different carburetor setups. From Pianoman's description, it sounds like he has the same carb I do.

Tom and Tirebiter are correct for this particular carb.

The only adjustment screw that my carb has is the idle screw. That's it.

The push-button looking thing is called a "tickler". I have an old Moto Guzzi motorcycle that has the same push-button ticklers on the carbs. Their only function is that when you hold them down for a couple seconds they slightly flood the carburetor on purpose to help it start when it's cold, but I never use mine, and actually plugged it with a screw to eliminate a possible source of leaks. (In case you are curious, they work like this: The button is connected to a pin that goes into the carb. Pushing the button pushes the pin, which pushes the carb float down. Pushing the carb float down makes the carb think the bowl is not full yet, so it pours more gas into the float, thus overfilling the carb. Holding this button down too long will cause gas to start leaking out through the button.)

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. Compress the spring, unhook the cable from the sliding cylinder, and take the needle out of the assembly. On the needle you will see 4 grooves. Putting the E-clip on the top groove lets the needle sit lower into the carburetor, which blocks the fuel flow, which leans out the mixture. Putting the E-clip on the bottom groove gets the needle up out of the way a little, which clears the way for more fuel to go through, which enriches the mixture. Top groove = lean. Bottom groove = rich.

I live about 3 miles from the ocean, which pretty much puts me at sea level. I find that my bike starts easiest and idles best with the E-clip on the second groove from the top. The top groove makes my bike harder to start and the bottom two grooves make it so rich that it spits a lot of unburnt fuel out of the tailpipe.

If you are at a high altitude, I have heard that you can get a new jet (the nozzle that sprays the gasoline) to adjust for altitude. Changing the jet would be really easy, but figuring out which one you need might be a pain. Hopefully you won't have to do this. Mine runs fine with the stock jet, so I have never had to mess with it.

Anything past carb adjustments might be some other engine stuff, so let us know what kind of problems you are having and I'm sure somebody here can help fix it.

So to sumarize:

The only thing the screw does is set your idle. Screw it in to make your bike idle faster, screw it out to slow the idle down. This screw will not affect anything else on your motor except idle speed.

The only way to adjust your mixture is to move the E-clip up and down the needle. Since it works so well for me, I'm going to suggest starting with the second groove down and work from there.
 
P

pianoman8t8

Guest
Hey, thanks for the info, blaze. When I assembled the engine and the carb and everything else, i don't recall seeing more rings, but i will definitely take a look when i go home this weekend or friday. I can't wait. Thanks again!

-Ryan
 
S

Steve

Guest
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tirebiter said:
Steve said:
I don't even pretend to know why, but if I set my idle screw at around 4 turns out, the engine has no power at wide open throttle. However, if I turn it out to 5 turns, the engine makes good power at wide open throttle. :???:
That's wierd Steve. All the idle screw does is stops the slide as it goes down into the throat of the carb. It hits a slanted slot so that screwing it in or out lets the slide stop up or down a little. As soon as you give it any throttle above idle it doesn't do anything.

Maybe you've got one of those secret carbs that the oil companies bought the patents to. :eek:
George,

I know, it should not, and technically speaking, cannot happen. But again, on mine it does.
 
G

gone_fishin

Guest
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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....
 
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