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2005 YZ250 carb issues

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I have read most of the threads here on YZ250 carb tuning, but I'm still confused as to what is causing my low end issues.

My 05 YZ250 is running rough on the bottom end.  We moved from Arizona last year to Idaho.  Obviously temperatures are quite different.  We regularly rode in 100-110 temps in AZ and now we're riding in 65-85 degree temps in Idaho.  Elevation is only slightly higher where I'm riding in Idaho.  2500-4000 as opposed to 2000-3000 in Arizona.

I'm quite versed in the effects of altitude and temperature on air desnsity, but I'm confused in how to go about cleaning up the bottom end.  The bike is very rough at times in the 1/8th to 1/4 throttle positions.  If I ride it hard it cleans up, but as soon as I start riding easy on trails, roads etc it comes back and starts running rough in the bottom end.  Mid range and top end are clean and crisp everywhere.  As I go up in elevation and temps cool more the bike runs better in all throttle ranges.  My question is how to determine if it's the temperature drop or the small elevation gain that is cleaning the bike up.  Obviously going up higher means thinner air, but that also means cooler air especially in Idaho.   For the amount of elevation gain I think it's the temperature change more than elevation.  

I have the standard N3EJ needle, stock pipe, pro circuit silencer, and run half ethanol free gas mixed 50/50 with Sonoco race gas.  When I pull the plug is dark brown and looks good.  What jetting, needle etc should I use and what air screw settings?

Any input is appreciated.

 

 

 

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I need to pull the carb this week.  I'll find out what clip position and pilot jet I have.  Is the pilot mainly controlling the 1/8-1/4 throttle range?

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The pilot jet size,  and air screw are the easy to change items that affect the low speed running.   Have you tried going in on the air screw and then back out again?  that should get you some idea of whether you are dealing with a rich or a lean condition.   Float should be set before you try anything though.  

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I had a crazy time trying to jet my bike (also in Idaho) come to find out I had a pin come out which caused one of my power valves to get stuck. Fixed the power valve, bike runs great. I've had plenty of success running the stock pilot jet for our Idaho elevation. Just requires a little more tuning with the Air screw when it gets hot. Though mines a 125. So I'm not real versed on the carb on yours. 

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Another leaning toward pilot jet or other problem. How long did gas sit in the carb?

Edited by Charles De Mar

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Thanks for all the replies!  All is very helpful.  I will take a look at the air screw setting and the pilot jet.  Gas and carb were drained this last winter while it sat.  I'll pull it off and clean it just to be sure and also check my jet sizes and clip position. Need a few days to get to it but I'll have more questions about it once I get it out.

Should I  switch to the N3EW needle while it's apart?  Does this lean out the bike?

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3 hours ago, Chalk said:

Thanks for all the replies!  All is very helpful.  I will take a look at the air screw setting and the pilot jet.  Gas and carb were drained this last winter while it sat.  I'll pull it off and clean it just to be sure and also check my jet sizes and clip position. Need a few days to get to it but I'll have more questions about it once I get it out.

Should I  switch to the N3EW needle while it's apart?  Does this lean out the bike?

No that is a richer starting needle

make the switch to a triple taper Suzuki needle and never look back

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6 hours ago, kxrob said:

No that is a richer starting needle

make the switch to a triple taper Suzuki needle and never look back

Which Suzuki needle are you talking about?

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20 hours ago, 506 yz125 said:

I had a crazy time trying to jet my bike (also in Idaho) come to find out I had a pin come out which caused one of my power valves to get stuck. Fixed the power valve, bike runs great. I've had plenty of success running the stock pilot jet for our Idaho elevation. Just requires a little more tuning with the Air screw when it gets hot. Though mines a 125. So I'm not real versed on the carb on yours. 

I just did a top end rebuild and cleaned the power valve so I'm pretty sure mine is working.  I did have this issue before the top end as well.

What part of Idaho are you in?  I'm in Coeurd'Alene.

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5 minutes ago, Chalk said:

I just did a top end rebuild and cleaned the power valve so I'm pretty sure mine is working.  I did have this issue before the top end as well.

What part of Idaho are you in?  I'm in Coeurd'Alene.

Nice! You ever ride with Bob Hannah? I know he's up there somewhere flying his planes around.

 I'm down closer to Boise. 

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Yes I do know Bob Hannah, but through flying.  He actually lives down near Boise.  Said he hardly rides a motorcycle anymore.  Great guy and fun to talk to!

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8 hours ago, 506 yz125 said:

Which Suzuki needle are you talking about?

that depends on elevation and temps

only work in keihin carbs tho not mikunis

7 hours ago, Chalk said:

I have heard of people using the Suzuki needle, but what are the effects?  

no 3/8 th throttle lean spot like the yamaha needle

cleaner bottom end 0-1/2 throttle

smooths out the hit 

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4 hours ago, Chalk said:

Yes I do know Bob Hannah, but through flying.  He actually lives down near Boise.  Said he hardly rides a motorcycle anymore.  Great guy and fun to talk to!

No way!! Yea I love watching his old interviews. Wish we still had a Hannah in today's motocross scene.

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Yes he's quite a character and full of energy still!

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I have finally pulled the carb and found the following......

air screw was 1 turn out

needle/N3EJ with clip 3 positions from top

pilot jet is 175

main jet is 48

What should I do to clean up that 1/8-1/4 rough running situation?  Bike starts and idles smoothly.  As stated when I started this topic, power is smooth everywhere except the initial  power dilevery under load and bottom end.  Mid and high range are good.

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2 hours ago, Chalk said:

I have finally pulled the carb and found the following......

air screw was 1 turn out

needle/N3EJ with clip 3 positions from top

pilot jet is 175

main jet is 48

What should I do to clean up that 1/8-1/4 rough running situation?  Bike starts and idles smoothly.  As stated when I started this topic, power is smooth everywhere except the initial  power dilevery under load and bottom end.  Mid and high range are good.

Pilot jet. Get a smaller one. 

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I have finally pulled the carb and found the following......
air screw was 1 turn out
needle/N3EJ with clip 3 positions from top
pilot jet is 175
main jet is 48
What should I do to clean up that 1/8-1/4 rough running situation?  Bike starts and idles smoothly.  As stated when I started this topic, power is smooth everywhere except the initial  power dilevery under load and bottom end.  Mid and high range are good.

What is the condition of your reeds?

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