Idle Mixture ?'s

[nebraskan]

After reading around and reading Vex's DIY on adjusting the idle mixture screws i decided that mine needed adjusted. when warmed up if i blipped the throttle it would hang for a little while before returning to idle. I have both screws at 2.5 turns out because that seemed to be the general consensus on where to set them, but it still hangs if i blip the throttle, and it runs fairly rough until i get past 5k. so, should i back the screws out a little more or is there anything else that i should check? any help will be greatly appreciated!

[kkim]

use this guide to fine tune the mixture screws. the 2.5 number is just a rough starting point from which to fine tune from.

http://faq.ninja250.org/wiki/How_do_...dle_mixture%3F

[nebraskan]

alright thanks i'll check that out and see how things turn out tomorrow

[kkim]

just be sure that the bike is thoroughly warmed up before you start adjusting the mixture screws to be assured of accurate results.

[nebraskan]

I'm just gettin around to doing that tomorrow but just to double check, if I can't get it fine tuned does that mean ill have to sync my carbs and/or have the valves adjusted?

[gfloyd2002]

Originally Posted by nebraskan

I'm just gettin around to doing that tomorrow but just to double check, if I can't get it fine tuned does that mean ill have to sync my carbs and/or have the valves adjusted?

It just sounds like you are a bit lean because of the revs hanging after throttle blip. Needs more fuel flow.

What exhaust are you running? If you have aftermarket, you need to do a bit more than adjust the mixture screws. Have you shimmed the needles, changed your needles or jets? The mixture screw adjustment can only do so much.

If you haven't done it yet, shimming will help get rid of the lean condition in a better way than messing with the idle mixture screws. Carb synching and valve timing of course possible causes for problems, but that isn't the first place I'd think.

[nebraskan]

Thanks gfloyd, I don't have an aftermarket exhaust but i suppose shimming the needles wouldn't be a bad idea anyways?

[gfloyd2002]

I think that will help significantly with what appears to be a lean mixture. Read this great thread to help you decide: Shimming needles: Is it for you?

[nebraskan]

i think i'll try shimming the needles. i'll start off with one 3mm washer on each and go from there, i'll keep you guys posted on how it goes. thanks for all the help!

[kkim]

adjust/fine tune your mixture screws. you can't just set them to a set number of turns and expect great results. it takes time and experimentation to get right. the hanging sounds to me like a too lean idle circuit. while shimming may solve your problem, you already have the means to fix your problem if you have access to the mixture screws.

it takes much less time and effort to adjust the mixture screws than to shim the needles... not to mention avoiding the potential problems others have had when shimming.

[nebraskan]

adjust/fine tune your mixture screws. you can't just set them to a set number of turns and expect great results. it takes time and experimentation to get right. the hanging sounds to me like a too lean idle circuit. while shimming may solve your problem, you already have the means to fix your problem if you have access to the mixture screws.

it takes much less time and effort to adjust the mixture screws than to shim the needles... not to mention avoiding the potential problems others have had when shimming.

alright, i'll just plan on that and if it doesn't work out i'll be back to ask some questions.

[kkim]

fine tune the mixture screws first and if that doesn't fix your problem, then move onto shimming the needles, if needed.

rereading your original post, I think you have partially blocked pilot jets that is causing your lean condition.... did the bike hang, like it is now, before you installed the slip on?

[nebraskan]

yes i still don't have a slip-on on and it hangs

[kkim]

sorry... thought that you had installed an aftermarket exhaust.

...which means your bike is totally stock and it hangs? have you done anything to the bike that would cause it to run leaner? how did you remove the mixture screw caps?

[wherewuat]

If and When you shim the needles, def be careful with the vacuum diaphragm.
Kelly def knows my struggles and just be CAREFUL not to pinch the vacuum
with the carb cap. the left side was my problem just fyi
and i know that they say that the diaphragm is very fragile, but don't be scared to handle it. just do it nicely haha.

[nebraskan]

I haven't done anything at all to the bike other than an oil change, but it would hang before i ever did that. I used Vex's DIY on taking off the mixture screw caps and made extra sure that i didn't drill too far, i didn't even go completely through the cap actually.

[kkim]

okay... a stock bike should not hang. define what you mean by "the bike hangs".

reason for being so picky here is that you should not be trying to tune your carbs unless they are running 100%, first. sounds like you might have another problem and are trying to compensate for it, which you should not do.

some of your bike's history?

[nebraskan]

When I was saying that "the bike hangs" I mean that if i rev the engine a little bit the rpm's will hang around 2k for a few seconds before slowly dropping back down to the idle, or if i'm driving and pulling up to a stop light and pull the clutch in the rpm's will hang around 2k for a few seconds before slowly dropping back down a little.

About the bikes history. I bought it from a car dealership in February with 2050 miles. They said that it had been sitting around all winter, so when after i drove it home i drained the gas, put new gas in, and added some seafoam. it was nice for about a week in february and i ran about 3 tanks of gas through it all with some seafoam added. it would sit around in a garage but not for more than a week without driving it. i changed the oil at 2350 miles using mobil 1 synthetic 10w-40 and a fram oil filter. I started looking around on here and KF because that whole time the bike was taking what seemed too long to start and too long to warm up. With that, on top of the rpm's hanging, is when i decided that maybe i needed to adjust the idle mixture screws.

[kkim]

okay, thanks.

I can tell you the mixture screws are most likely not optimized at this point, possibly leading to the too lean condition. use the link I provided earlier and set the idle mixture screws using the "alternate" method outlined in that link.

setting both mixture screws to the same 2.5 turns most likely made your condition worse. Stock bikes use 2 different needles in the left and right carbs and as such, even the stock mixture screw settings differ to compensate for that slight difference. I advise you let the bike tell you what the mixture screws should be set to based on how the revs return to idle.

you should be able to dial out that hesitation of returning to idle by fine tuning the mixture screws. let us know how it goes.

I also recommend you check the carb sync and adjust if it is off.

[nebraskan]

alright thanks kkim i'll let you know how it goes

[nebraskan]

Real quick question, i'm going to try and take care of this tomorrow- should I check the sync of the carbs before or after i adjust the idle mixture screws?

[kkim]

do the sync, then the mixture screws. after you're done with the idle mixture adjustment, recheck the sync.

[red]

Kelly is likely spot on.

I had a similar problem on hanging decel on a relatively new bike. I could not figure out. I and already set the idle mixture screws out to 2.5 but it still ran poorly.

I ended up pulling the carbs and checking everything. The first time through it was about a 5 hour exercise for me with the fairing removal, loosening the airbox, pulling cables, and extracting the carbs, checking, then doing the reverse. Not terribly difficult but not much room either.

Made sure the pilot jets were clean, went ahead and shimmed 2 #4 washers under the needles, reset the mixture screws to 2.75 turns out and adjusted out way too much slack what I am guessing was a too loose throttle return cable that may have been binding, and the thing now runs like a dream with a quite a transformation. I am guessing it came from the factory with the return cable mis-adjusted.

Maybe the same will resolve yours.

[nebraskan]

okay so i checked the carbs and the sync was good, i adjusted the idle mixture screws out and i pretty much got rid of the hesitation that i had. I checked the sync after adjusting and it was still good. My bike still seems to run a little rough under 5k. any advice?

[kkim]

Originally Posted by nebraskan

okay so i checked the carbs and the sync was good, i adjusted the idle mixture screws out and i pretty much got rid of the hesitation that i had. I checked the sync after adjusting and it was still good. My bike still seems to run a little rough under 5k. any advice?

can you explain that a bit more? when does it happen... is the bike fully warmed up... what does it feel like??

have you done any other intake or exhaust mods to the bike?

what mixture screw settings did you end up with?

air filter clean?

[nebraskan]

It usually happens before the bike is completely warmed up. The under 5k it jerks a little bit- like i can accelerate and have the throttle in the same position but it will be jerky and not smooth, and when i hit 5k it will just take off. the bike is completely stock. i have the left screw adjusted out to about 3.5 turns and the right to about 3. and the air filter was clean.

[kkim]

how does the bike idle when thoroughly warmed up?? nice and steady or kinda erratic/choppy?

what do you have your idle rpm set to?

[nebraskan]

when it's warmed up its a lot more steady but still not incredibly smooth. the idle rpm is set right around the suggested 1350

[kkim]

the bike will normally be kinda jerky at the lower end before it has a chance to warm up. Normally, you can leave the choke on as you ride and turn it off after you feel it has warmed up.

your mixture screw settings seem a bit rich for a stock bike, indicating a possible air leak somewhere. double check to see if you have your vacuum hoses all hooked up and correctly connected. also check the carb clamps for tightness at the engine and airbox sides of both carbs.

if everything checks out and you want to try and improve what you have, shimming, as suggested earlier, may help with your under 5k stutter.

I would recommended trying 2 shims on each needle to start with.

[nebraskan]

I was told that there could possibly be an air leak by amechanic down here so I checked and everything seems hooked up fine. Ill double check the clamps though. And for the washers should I use two 3mm or two 4mm?

[kkim]

Originally Posted by nebraskan

I was told that there could possibly be an air leak by amechanic down here so I checked and everything seems hooked up fine. Ill double check the clamps though. And for the washers should I use two 3mm or two 4mm?

washers should be 3mm. that's almost equivalent to SAE #4.

4mm washers are too big. DO NOT USE 4MM WASHERS.

[nebraskan]

DO NOT USE 4MM WASHERS

I didn't think those were right but I read somewhere that some guy used them