Newbee question (idle mixture)

[bigconig]

Can someone please tell me where the idle mixture screw is on an 07. I just rejetted after airfilter exhaust and I think I have the main just about right but my idle circuit seems lean.

The owners manual only shows idle speed adjustment and I'm awaiting delivery of my service manual so for now I'm in the dark.

Any help would be appreciated.

BC

[klutchbuster250]

if your talking about teh pilot jet wich controls the idel and lower rpms then its the smaller jet right next to the main,u should see it when u change the main jet i think u gottta take out the the pink thing in the float bowl like were the main jet is to see it

[klutchbuster250]

o and wut pipe did u get couse i have a full hmf and filter and i jetted it just right and i never had to chage the pilot i bet u dont need to eaither just adjust the idel speed

[bigconig]

Thanks for the reply klutch, I got a Curtis sparks full system and a UNI filter. So the idle speed screw (on the right side of the carb) will adjust for a lean condition and not just rpm of idle? From every thing I've read I should be fine with the stock pilot jet like you said so I was a little surprised by this.

Oh yeah, in case I'm totally screwed up here, I'm getting popping on deceleration, that's why I think the idle is lean.

[klutchbuster250]

if its not poping to bad ur good my bike does the same, and wut exactly does ur bike do,when u leave it ideling does it like idel and sounds like its gona shut off?if thats the case just turn up ur idel and ur idel wont lean anything out , try and see if it fixes ur problem

[bigconig]

I think I edited above while you were replying. It actually idles very nice, it's just the popping while I'm off throttle and moving in gear.

[klutchbuster250]

if its poping on decel and when u let of the gas ur runing lean but if its not poping bad dont worry, r u running a airbox lid?

[bigconig]

yup, lid's on. I actually have the quiet core coming (the system is louder than I expected, but sounds real nice) I imagine that will richen the mixture up a bit when I add it, so that might help too.

[jrafter]

i put a curtis sparks full system and K&N filter on my kids 250.

had to shim the needle jet......it would start and idle great but it popped and sputter in mid throttle and decell.

i should have gotten a jet kit.....jetting ended up being

97.5 main
stock pilot i think it a 42
and shimed the needle

[tedwilley]

Good info on jetsrus.com.
The fuel mixture screw is on the bottom of the carb. It takes a 'D' shaped socket tool. If it is not frozen up, you can turn it with a small flat blade screw driver, carefully. Standard adjustment is all the in (to the right), then back out 2-1/2 turns. Go from there.
According to jetsrus, popping on deceleration can be fixed with a larger pilot jet, but there should be enough adjustment with the fuel screw. I was able to move the clip on my needle and adjust the fuel mixture screw to stop any popping.

[bigconig]

Thanks Ted- I saw that and wondered about it, not having a normal screw really threw me. I think I may have to pull the carb to get at it, or at least find a screw driver that's considerably shorter than anything in my kit.

Also, I couldn't locate the needle, I saw someone else on here with an 07 who said the same thing- I thought it was under the main jet. Am I way off or is there a chance that the 07+ are different?

[tedwilley]

The needle is inside the throttle slide on top of the carb, where the throttle cable is attached. Loosen the collar to draw out the slide. After removing the slide from the cable assembly, look down into the slide. You will see a plastic disk on top of the needle. The disk has a slot in each side, and it sits in a groove inside the slide. Remove the disk using needle nose pliers to grasp the small center 'knob' and squeeze the disk, the slots allow the edges of the disk to come out of the groove when you squeeze. Be careful there is a very small spring under the disk.
Assembly is the reverse.
**If you do not have an after market needle there won't be any adjustment grooves, at least on the later models.
On the adjustable needle, there area series of grooves cut into the top with a small c-clip in one of the grooves. This clip holds the needle at a different heights when the throttle is closed. The needle is tapered and fits into a tapered hole on the carb. The closer the clip is to the top of the needle, the farther into the hole the needle extends and vice versa. The differences are in hundredths of MM. The clip adjusts not only how far the needle protrudes into the carb, but because the needle is tapered, it also adjusts how far the needle moves when the throttle cable pulls the throttle slide up.
Placing the clip closer to the top is leaner, further from the top is richer. be sure the clip is seated correctly on the needle, if it falls off after you assemble the slide, you will have noticeable fuel problems. The slide has two grooves machined into the bottom, one is tapered, i.e. it gets shallower from the bottom of the slide to where it ends. The slide only goes in one way. The tapered groove goes on the side where the idle speed adjustment screw is located. Don' force the slide, when it is correctly aligned it will go in easily.
Also don't over tighten the collar it can be stripped!
The needle controls fuel from 1/4 to 3/4 throttle and is the the only variable jet on the carb. Wide open (WOT) uses the main jet. The pilot jet is for idle, and the fuel screw under the carb adjusts that jet.
Starting point adjustment setting to try are clip on the third slot from the top, fuel screw 2-1/2 turns out from fully closed (all the way in). Any modification that lets in more air will require more fuel (exhaust, filter, airbox lid, etc). You altitude is also a factor. The higher your average elevation from sea level, the less air for you engine, so it will run richer. The carb setup that works great at 100 feet above seal level will be too rich above 3000 feet, for example.
For an more official explanation of motorcycle type carb jets look on jetsrus.com.
It is pretty simple, even if I may have made it sound complicated.;)
After the first time, it will take longer to remove the seat and airbox than to adjust the needle!

[tedwilley]

bigconig,
Let me also add that jetting can be different for two identical engine setups running in the exact same location, let alone all the different combinations of after market filters and exhausts (and brands of jets). That being said, the jetting for the two identically setup engines at the same elevation is not going to vastly different, i.e. 98 for one and 125 for the other! Also, the exhaust mfrs notoriously suggest main jets way too large, at least for the little 250ex with only bolt on mods..
Try to find someone who has the most similar setup at an elevation close to where you ride and use their jets and clip setting as a starting point.
Running too rich will foul your plug, worst case you would need a new spark plug. Running too lean for a long enough period and you will run hot, and possibly begin to burn the exhaust valve. Air cooled engines are more susceptible to burnt valves from running too lean
It is always easier to let it run too lean because the engine seems to run great and that popping sounds 'cool'
I normally ride my '07 between 150 to 3000 feet above sea level.
I have an HMF full exhaust system, K&N filter with an outerwear pre-filter, no airbox lid , and Dynojet jets.
Main jet: 112
Needle: 3rd position
Pilot: stock
Fuel screw: 2-3/4 turns out
With these mods, I started with stock jetting and went up from there. Use common sense. Spark plugs are cheap and easy, valve jobs are not.

[bigconig]

Thanks Ted, that clears up a lot of stuff. I got at the idle screw and it seems a 1/2 turn did the trick there. No more popping :)

I got a chance to run her tonight and it seems it might be a little lean on the main jet now (It was a little cooler than it's been) But now that I've been in there a couple times bumping that up a step or two will be quite easy. I'll check the needle (now that I know where it is) while I'm doing that.

Thanks again to all who chipped in, You guys have been a great help!!:cool: