TE-250 2010 idle air bypass

R_Little · Nov 3, 2011

I noticed this adj screw on the side of my throttle body and noticed it raised the idle speed when my bike was flaming out.

I not see on this site that it is NOT supposed to be used to adjust idle speed but idle mixture.

Is that true?

I'm running 107 on Co1 and still have a bit of off idle studder.

I'm going to use I-Beat to set TPS this weekend and need to know if I need to reset this idle air bypass screw as well.

thanks!

HUSKYnXJnWI · Nov 4, 2011

I assume you are reading what is quoted below. The AIR BYPASS does effect idle and idle mixture. WHat Mat is suggesting is not to think of the AIR BYPASS Knob as only effecting rpm. There is alot that goes into what your RPM will be at idle- it is a collective of many facets #1,2,3,5 below explain. SO ultimately once you have your bike set up to the correct WOT setting with your TPS dialed in- and you are set at the correct CO1 setting- then you would use the air bypass to dial in the low end/idle mixture (think of it that way) if you try to raise or lower the rpms significantly with that goal souly in mind- you will loose the proper mixture and performance will suffer. So once set up "think" of the air bypass more as a "fuel screw/airscrew" (in leaner/out richer in this case)- but it was really intended to set the idle. But it does this by adding/subtracting air- which effects mixture as well. Make sence? read Mats points below a coulple times he brings the whole spectrum together and how it effects parts of the spectrum-

bbcmat said: ↑

A follow up to this DIY tweak. (on my 09 TE510)

I went through this exercise before I had access to Ibeat V2 - after using the software and gaining experience with it over all seasons and weather - here are some opinions.

1) the most stable tuneup has a TPS setup of 100.2% at full throttle and the idle position set to whatever postion achieves that number (my bike = 1016mV). DIY tweak not required.

2) the bike will hot idle at 1950-2050. That's the way it is. Techniques to lower the idle make the bike very sensitive to idle air bypass screw positions. I'm not fiddling with that as the air density changes morning to noon to night. I will turn it out to 4 turns when warming the bike up in freezing temperatures.
Overall - this has as much to do with the ignition timing curve as the fueling.

3) The idle air bypass should be used to set the idle air mixture - NOT the idle rpm. Mine runs best 2 3/4 turns out plus minus 1/2 turn depending on the day and the ride. Hot slow singletrack needs more air (turn screw in) Cold street riding needs less air. The most consistant way to set the position is to move it to optimize your hot start. The motor should immediately fire off the crank button and jump to idle rpm. If it struggles to start or slowly increases in rpm to idle - give it 1/8 - 1/4 turn in until it starts best. 90% of riders probably won't bother - it's effect is only in the first 5% or so of throttle. (off-idle transition). If it takes more than 1/2 turn then CO1 need to be reduced .3% or so.

4) When your tuneup is close - changes to the exhaust make a difference. Mine will "surge" around 28-3000 rpm if i remove the spark arrestor - perfect if I put it back. I can move the surge around with c01/co2 but it never disappears.

5) I set co1 lean enough to make it hesitate under snap off-idle throttle openings - then add .3% if dual purpose riding or .8% if tight single track riding.

6) I set co2 just lean enough to remove the constant throttle surge in 6th gear at 3-3300rpm. This is my off-road setting. I'll lean that down 1 to 1.5% for street riding

7) I set co3 at 100%. I run this a tad rich - the excess fuel provides cooling and detontation resistance without much loss in power or range. I've give up the small % of power as insurance.

MAT

HUSKYnXJnWI · Nov 4, 2011

Ultimately- when I am going to ride in HOT conditions- tight single track on a HOT day with little airflow- I will turn my bypass in 1/4 turn if I notice it needs it- or out in cooler temps/open terrain. its not often that I need to make any adjustments to it though- so you are doing about the same thing- maybe after you adjust the TPS it will be more stable.

R_Little · Nov 14, 2011

My TPS was 102.4 @ 925mv.

100.8 @ 1030mv made the idle super high.

I am at 101.2 @ 1016mv right now.

The studder is just gone at this setting.

the lower TPS seemed to have richened the bike up at idle.

I need to reset the CO2 and CO3 now.

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TE-250 2010 idle air bypass

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TE-250 2010 idle air bypass

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