250ex Carb adjustments

[AZriders]

I just purchased a used 2004 250EX for my wife and was trying to adjust the idle because it was idling too high and when I put it in gear it would "bang" hard. I think I got the mixture setting wrong and now it falls on its face at high rpm. I don't have a manual and can't seem to find any web links to adjusting the carb. Of course pictures would help. There's a small screw on the bottom of the carb and a larger screw on the side (near the exhaust pipe). Which controls the idle and which is the mixture?
Thanks!

[GPracer2500]

The larger one on the side should be the idle screw adjustment. The little one on the bottom (should be on the engine side of the carb) is your fuel mixture screw.

The fuel mixture screw only affects the pilot circuit (works in conjunction with the pilot jet) and affects fueling from 0 to about 1/8 throttle.

Check out these links for getting started on learning about carburators:
http://www.exriders.com/vbb/showthread.php?s=&threadid=221803
http://www.exriders.com/vbb/showthread.php?s=&threadid=221872

Follow the links in the first link for more info on the basics.

[ryanh250ex]

Originally posted by GPracer2500
The larger one on the side should be the idle screw adjustment. The little one on the bottom (should be on the engine side of the carb) is your fuel mixture screw.

The fuel mixture screw only affects the pilot circuit (works in conjunction with the pilot jet) and affects fueling from 0 to about 1/8 throttle.

Check out these links for getting started on learning about carburators:
http://www.exriders.com/vbb/showthread.php?s=&threadid=221803
http://www.exriders.com/vbb/showthread.php?s=&threadid=221872

Follow the links in the first link for more info on the basics.

what he said

i disagree, i feel that the fuel screw affects the entire rpm range.

it sounds like you messed with the fuel screw. richen it back out and drop the idle back down.

[AZriders]

Thanks for the info!!! Turns out the idle problem was at the throttle linkage on the handlebar. The nut came loose and as soon as I touched it the idle came down. From there I was able to get the settings back. Thanks!!!

[GPracer2500]

Originally posted by ryanh250ex
[snip]...i disagree, i feel that the fuel screw affects the entire rpm range...[snip]

Ya know, you're techincally right about the pilot circuit (of which the fuel screw is a part of). Let me clarify what I meant:

The pilot curcuit DOES contribute a small amount to the entire throttle range (carb circuits relate to throttle postitions NOT rpm ranges). BUT, the pilot circuit should only be used to change the fueling from 0 to about 1/8 throttle as it is the PRIMARY circuit for those throttle positions. It has a very small affect at larger throttle postions compared to the other curcuits.

If you need to change the fueling at middle or wide-open throttle settings than there are other carb circuits for those ranges. Each circuit dominates certain throttle postions. Sure, there is some bleed over between the circuits, but you set each one independently. The pilot circuit should be optimized first, then the needle profile and clip position, then the main jet.

Look at it this way: When the throttle is wide open and the main jet is flowing its full load of fuel, the pilot circuit is also flowing its full load of fuel. So if you richen the pilot ciruit than you have also added some fuel to cumulative flow at full throttle. That's how the pilot curuit effects the entire throttle postion range. But if you richen your pilot curcuit to add some fuel flow in the middle or upper throttle openings then you're changing your pilot circuit when you should be changing the needle or main jet--and now your pilot circuit is off.

That's why you set your pilot first (for small throttle openings) then move along the respective carb circuits to meter the fuel for progressively larger throttle settings. That's the ideal way to jet most carbs.

When someone says "falls on its face at high rpm" they are generally at large throttle openings dominated by the main jet and the pilot curcuit is not the appropriate adjustment point.

That's what I was trying to get at.

[ryanh250ex]

Originally posted by GPracer2500
Ya know, you're techincally right about the pilot circuit (of which the fuel screw is a part of). Let me clarify what I meant:

The pilot curcuit DOES contribute a small amount to the entire throttle range (carb circuits relate to throttle postitions NOT rpm ranges). BUT, the pilot circuit should only be used to change the fueling from 0 to about 1/8 throttle as it is the PRIMARY circuit for those throttle positions. It has a very small affect at larger throttle postions compared to the other curcuits.

If you need to change the fueling at middle or wide-open throttle settings than there are other carb circuits for those ranges. Each circuit dominates certain throttle postions. Sure, there is some bleed over between the circuits, but you set each one independently. The pilot circuit should be optimized first, then the needle profile and clip position, then the main jet.

Look at it this way: When the throttle is wide open and the main jet is flowing its full load of fuel, the pilot circuit is also flowing its full load of fuel. So if you richen the pilot ciruit than you have also added some fuel to cumulative flow at full throttle. That's how the pilot curuit effects the entire throttle postion range. But if you richen your pilot curcuit to add some fuel flow in the middle or upper throttle openings then you're changing your pilot circuit when you should be changing the needle or main jet--and now your pilot circuit is off.

That's why you set your pilot first (for small throttle openings) then move along the respective carb circuits to meter the fuel for progressively larger throttle settings. That's the ideal way to jet most carbs.

When someone says "falls on its face at high rpm" they are generally at large throttle openings dominated by the main jet and the pilot curcuit is not the appropriate adjustment point.

That's what I was trying to get at.

ah, no worries mate we're on the same page :cool:

[GPracer2500]

Originally posted by ryanh250ex
ah, no worries mate we're on the same page :cool:

:)