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I recently purchased a brand new 2015 CRF250X. Since purchasing I installed the JD jet kit, and completed the air box mod. I live and ride in Kentucky, between 800 - 1200 feet above sea level, with the temperatures ranging from upper 70's to high 90's. I followed the JD jetting instructions and replaced the stock main jet with a 158 main, the pilot jet was changed with the 42 that came in the kit, and I replaced the stock needle with the red needle, with the clip in the fifth position from the top. I also removed the stock air mixture screw and replaced it with a R & D racing flex jet fuel screw backed out 1 3/4 to 2 turns. The bike has completely stock exhaust, with the OEM air filter. The bike seems to run alright, but there are a few things that I have some questions on.

  • Before doing the mods to the bike you could pull the hot start lever all the way in and the bike would die. But now since doing the mods the bike will idle faster once the hot start lever is pulled in all the way.
  • The same thing happens with the choke lever. Once the bike is good and warm if you pull the choke out the bike at first doesn't really do anything, but once you give it some throttle it will idle faster.
  • The bike now has a backfire problem, which I never noticed before I did the mods. The backfire isn't necessarily a high pitched loud popping sound, but more of a low sound, almost like a large amount of air is being forced out. I've noticed the backfiring mainly happens when decelerating, or when dropping gears too quickly. My 250X does have the smog equipment attached. 
  • If I stall the bike while out riding it seems to be very hard to start, and most times I have to pull in the hot start lever to get the bike started. Before the mods I never used the hot start after I stalled the bike. As I try to restart the bike back it makes the same backfire noise like it does when I am out riding.
  • The idle speed seems to not stay consistent. I'll warm the bike up and check the Works Connection hour meter and it will be reading around 1800-1900 RPM. Once I've been riding for some time, and come to a stop, the RPM meter will be reading more in the 1700 range. The RPMs at idle don't stay constant, I find myself adjusting the idle screw a few times while out riding. 
  • I am also having the problem of the bike randomly stalling. For example, I could come to a stop with the clutch engaged, sit still for a few seconds, and when I give the bike a little rev it will stall and die. The throttle doesn't even come open when it stalls, I just barely give it a turn and it will die. Like stated before, when this happens the bike is hard to start back, and backfires when trying to be started. 

I have tried playing around with the fuel mixture screw, but nothing seems to correct the problems I am experiencing. The bike seems to run fine other than the stalling and backfiring. I am not sure if changing jet sizes or clip position would correct the problems I am having. I have tried researching these topics, but nothing seems to be like what I am experiencing. Any advice would be greatly appreciated. 

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You are running rich on the slow circuit.

With the motor warmed up:

1. Lower the idle till just running.

2. Adjust fuel screw to get smoothest running.

3. Repeat one and two until you can't keep it running

4. Raise idle to 1,700 rpms.

 Screw should end up between 1 and 2 1/4 turns.   If you don't, then you need a different slow jet for your conditions.   Note that you may want to put a fan blowing on the radiator to keep it from over heating as you do the above.

 When you are spot on, you should be able to:

1. Pull the hot start slightly and get a rise in RPM's

2. Pull it all the way and the motor should die.

3. Pulling the choke should kill the motor.

If you have not removed the PAIR (smog pump), then you will get popping on decel.  It job is to put air into the exhaust to burn any un-burned fuel mix in the exhaust.   If you have removed it and still get popping or have a hanging idle (let go of the throttle and it idles high, then drops down), go 1/4 turn out on the fuel screw.

Get that adjusted first and then see if you still have the problem with stalling off idle.

Jim.

 

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You said the bike was brand new and you recently got it. Did you have issues before you rejetted that caused you to mod it?

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They aren't really built to run in stock form. They are built to run lean enough to pacify the EPA so that they are allowed on public land in California.

I have measured the air fuel ratio on a stock bike at 18-1, and it should be closer to 13-1.

Edited by Leardriver

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23 minutes ago, Leardriver said:

They aren't really built to run in stock form. They are built to run lean enough to pacify the EPA so that they are allowed on public land in California.

I have measured the air fuel ratio on a stock bike at 18-1, and it should be closer to 13-1.

My owners manual lists California models as a separate bike though from the 49 state and Canada version.

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They are all jetted lean, but the CA model even more so and with some cam mods to boot in order to meet CARB requirements. This was on earlier models.   Not sure if it's the same across the board now or not (believe it is).  CA model  was also the first model to have the PAIR on it, although now all have it.   And it's not only CARB in CA, but the EPA as well where they need to meet emission standards.

 Both my 250x and 450x were totally different bikes after re-jetting and ran a lot cooler.  With the 450x, from day one it was always 50-50 if it would stall off idle.

Jim.

 

 

Edited by Jim Dettman

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I think that they are jetted lean from the factory, but not dangerously so. By all means the bike is made to mod. I am merely suggesting an alternative. The only thing I have done on my bike mechanically is remove the PAIR valve and add a fuel screw. I have it dialed in right now with the fuel screw at an average 1 1/4 turns out to: (Jim's words earlier)

"When you are spot on, you should be able to:

1. Pull the hot start slightly and get a rise in RPM's

2. Pull it all the way and the motor should die.

3. Pulling the choke should kill the motor"

 

So I feel there are options. I never thought I would be turning in the fuel screw either, but I've tested and retested and this is where the bike really shines. So I leave it there and just shrug my shoulders and ride it now.

 

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On 7/17/2017 at 11:11 PM, GFinch106 said:

1 - I recently purchased a brand new 2015 CRF250X. Since purchasing I installed the JD jet kit, and completed the air box mod. I live and ride in Kentucky, between 800 - 1200 feet above sea level, with the temperatures ranging from upper 70's to high 90's. I followed the JD jetting instructions and replaced the stock main jet with a 158 main, the pilot jet was changed with the 42 that came in the kit, and I replaced the stock needle with the red needle, with the clip in the fifth position from the top. I also removed the stock air mixture screw and replaced it with a R & D racing flex jet fuel screw backed out 1 3/4 to 2 turns. The bike has completely stock exhaust, with the OEM air filter. The bike seems to run alright, but there are a few things that I have some questions on.

  • 2 - Before doing the mods to the bike you could pull the hot start lever all the way in and the bike would die. But now since doing the mods the bike will idle faster once the hot start lever is pulled in all the way.
  • 3 - The same thing happens with the choke lever. Once the bike is good and warm if you pull the choke out the bike at first doesn't really do anything, but once you give it some throttle it will idle faster.
  • 4 - The bike now has a backfire problem, which I never noticed before I did the mods. The backfire isn't necessarily a high pitched loud popping sound, but more of a low sound, almost like a large amount of air is being forced out. I've noticed the backfiring mainly happens when decelerating, or when dropping gears too quickly. My 250X does have the smog equipment attached. 
  • 5 - If I stall the bike while out riding it seems to be very hard to start, and most times I have to pull in the hot start lever to get the bike started. Before the mods I never used the hot start after I stalled the bike. As I try to restart the bike back it makes the same backfire noise like it does when I am out riding.
  • 6 - The idle speed seems to not stay consistent. I'll warm the bike up and check the Works Connection hour meter and it will be reading around 1800-1900 RPM. Once I've been riding for some time, and come to a stop, the RPM meter will be reading more in the 1700 range. The RPMs at idle don't stay constant, I find myself adjusting the idle screw a few times while out riding. 
  • 7 - I am also having the problem of the bike randomly stalling. For example, I could come to a stop with the clutch engaged, sit still for a few seconds, and when I give the bike a little rev it will stall and die. The throttle doesn't even come open when it stalls, I just barely give it a turn and it will die. Like stated before, when this happens the bike is hard to start back, and backfires when trying to be started. 

I have tried playing around with the fuel mixture screw, but nothing seems to correct the problems I am experiencing. The bike seems to run fine other than the stalling and backfiring. I am not sure if changing jet sizes or clip position would correct the problems I am having. I have tried researching these topics, but nothing seems to be like what I am experiencing. Any advice would be greatly appreciated. 

I have the 2016 with a trail tech on mine to track km's and rpm's. I rode 1400 km's this year before the mods you are describing (stock setup), and 200 km's since the mods.

1 - Same as you, JD jetting jets as you described / instructed by the instructions, 4x4 inch air box mod, same elevation / riding temperatures. I installed the Tusk Fuel screw instead of the R&D, but use a twin air filter with bel ray air filter oil...everything else is stock just like you from an engine / intake / exhaust perspective.

2 - I never tested that, so I'm not sure what mine did.

3 - Pulling choke lever simply makes mine idle faster, it never dies

4 - I had this problem before and after the mods, I noticed no difference. I did purchase the tokyo mod smog removal kit, been holding off on installing it to get my jetting / mixture bang on before introducing this variable, but it should fix the backfire from what I've read.

5 - I noticed the same problem.

6 - Once the bike is warm, I dont have to mess around with it for the rest of the day. I usually need to have it a bit higher to start it, once warm I get an extra 500'ish rpm I need to dial out from the idle screw. Try running your idle at 1900 rpm.

7 - Same issue before and after the mods. If I idle at 1800-1900 rpms, I don't have this issue. The bike really doesn't like the suggested RPM setting of 1700 as per the manual. Give that a try?

My first outing with the mods I had my fuel screw at 2 turns. 55 km's into our ride I ran out of fuel, flipped it to reserve. Before mods I would easily get 80 to 90 km's before flipping to reserve. Since we were really far from the car, I was worried about range and turned my fuel screw in a full turn, so I was now 1 turn out from seated. I managed 5 km's of trail and 30 km's on a fire road back, with maybe a few oz of fuel left in the tank, it was almost empty. During the first 55 km's, I noticed my idle hanging a lot more then usual but didn't really pay attention to my rpm.

2nd outing this past Monday, I had my fuel screw at 1 3/4 out, the bike ran fine, hanging idle wasn't as bad, but I had a low rpm bog issue, a really bad one, 2nd gear up steep climbs would just bog on me. It was 30+ celsius and humidity was at 100% all morning, so I'm not sure if that had an effect, but recall turning it in another 1/4, so I was at 1.5 turns out and it ran better, but before I could test it again on climbs that day I took a bad dive and sprained my ankle, so I didn't get to play more with it.

 

Seeing Jim's reply, I decided to go adjust it based on the 3 tests you mentioned. Between 0 and 1.5 turns out, I was able to successfully do

1. Pull the hot start slightly and get a rise in RPM's

2. Pull it all the way and the motor should die.

I was able to repeatedly do 1 and 2 at 100 rpm's increments from 1600 to 2000.

As for the 3rd test, it doesn't matter what I try, pulling the choke simply doesn't kill the motor. I tried it at full in, then 1/4 out increments to 2 turns out and this would never happen.

My fuel screw full in also allows my bike to run, the rpm isn't as smooth, but it still runs. I'll reach out to JD, unless someone has a recommendation? From what I've read I think our 158 main might be too big, we should go smaller main, is that correct?

Nehoot, hope that helps with your troubleshooting, these are my discoveries so far.

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Thank you all for the helpful information. I have not been able to work with the bike since posting due to work. I purchased a smog removal kit from Applied Racing and it should be here by Friday. I am hoping to install it this weekend and try adjust my fuel mixture screw to get the bike running properly. I thought about removing the aftermarket fuel screw to make sure the o-ring and other components were in their proper places, and also of trying the stock fuel screw to see if I get a change in the performance of the bike. 

Steph7 - My bike also will still idle with the fuel mixture screw turned all the way in. I've never put too much thought into it, but I am also not an expert on the topic. I've also noticed that the bike likes to idle more in the 1800-1900 RPM range, sometimes even around 2000, but the manual does state 1700 +- 100. 

Edited by GFinch106

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Couple of points to consider:

1. You need to be careful when raising the idle past 1,700 rpms not to throw your results off.   What your doing when you raise the idle is raising the slide.   At some point, other circuits in the carb will start to kick in and adjusting the fuel screw and slow jet are not the only things in play.   That's why you lower the idle, then adjust, and repeat.    The TPS also starts coming into play a bit and adjusting the timing.   Technically for proper carb adjustment, the TPS is supposed to be disconnected.   

2. On:

" right now with the fuel screw at an average 1 1/4 turns "

  That's fine.   There's no hard and fast rule here, just a general rule of thumb to keep it in the range of 1 to 2 1/4 or turns out.   Reason?  Below 1, the tip of the fuel screw is so far in the hole that it is no longer effective in making adjustments.   Reason for not going beyond 2 1/4 is that the fuel screw can vibrate out.    If your below 1, then you go to a smaller slow jet, and if above 2 1/4, a larger one.

  It's rare though to need something other than a #42.   And by the way, if you mess up on the sequence of spring, washer and o-ring on the fuel screw, you will be lean as air will leak past.  The other thing to watch out for is if you every loose track of the o-ring, take a mirror and make sure it's not stuck up in the carb.   Many will loose an o-ring and assuming it's on the floor, toss another one on and end up with more than one in the carb.

3. On:

"3 - Pulling choke lever simply makes mine idle faster, it never dies"

  That's odd.  Where you want to be on the slow circuit is slightly rich.   That's why when you pull the hot start slightly and you lean out a bit, you get more rpms, but pulling all the way leans it out enough to kill it.    The flip side then is that pulling the choke should make you so rich that the motor can't run.

  Again, this should be on a warmed up motor, idling at 1,700 rpms.   If your outside of that, then you might not see the correct result.   If you are, then it would suggest the coke circuit is not rich enough (and there is a jet for that).

4. On:

" Before mods I would easily get 80 to 90 km's before flipping to reserve. Since we were really far from the car, I was worried about range and turned my fuel screw in a full turn, so I was now 1 turn out from seated. "

 What your going to find contributes  most to fuel mileage is how often you twist the throttle quickly vs rolling it on.   Twisting quickly activates the accel pump and it pumps in a hefty squirt of gas when you do that.  That will use up fuel quickly.   You should not be adjusting the fuel screw to conserve on gas.

This is also something to be aware of when dealing with bog off idle; if it's a quick twist and bogs, it's the acel pump that needs adjusting (leak jet).  If it's a slow roll and bogs, then it's the other carb components that need adjustment.

 For what it's worth, here's what effects what in the carb (click on the image to blow it up):

post-231688-0-92062800-1363528365_thumb.jpg

 

 Carb tuning is done from the top down, staring with the main jet, then moving onto the needle, it's taper, clip position (height), and diameter.   Slow circuit is done by itself last as well as the choke circuit.

 Also, you should not be expecting anywhere near the same mileage after the re-jet as before.   

Edited by Jim Dettman
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1 - Retested at 1700 RPM.  1  1/4 definitely sounds / runs the best and still get the engine to rev on a slight pull of the hot start and the engine dies when I pull it all the way.

2 - I learned how to take the carb off the bike for exactly this reason. I read too many people struggle to get the tamper pin off and oem screw out properly, including the o-ring as you mentioned. We triple checked before installing the new fuel screw.

3 - This is still a problem.  Slow circuit = Fuel screw?  At 1  1/4 slightly pulling the hot start raises idle, pulling all the way kills it. If I turn out further then 1  1/4, I can't kill the engine with the hot start lever. The choke never kills the engine, regardless of my fuel screw position.

The coke circuit being what jet when looking at the diagram, or did you mean choke circuit? What do you recommend I try?

4 - Looking at your diagram, I get it now. I definitely still have a quick twist bog issue. The bike is warm, and 2-3 blips its fine, then bam it dies on the 4th one. It seems I have a 20% chance of the bike dying in a quick throttle blip, at 1700 RPM's idle, at 100-110 celsius temperature, which replicates the issue I was having on my 2nd outing while riding.

 

In addition to the above, I also got a hold of the JD guys. Given how "new" this bike is and the bog only started with these changes, he recommended I ditch the tusk fuel screw and try something made out of brass, like my stock screw, the Scott's or the R & D...my stock is a bitch to adjust and I don't have the proper tool for it, so I ordered the R & D, and we'll see if that fixes my bog. If that doesn't work, he suggested I try the needle clip on the 4th position instead of 5th.

 

I'll give an update next week once the new screw is in and give that a try.

Again thanks for all the insight and assistance, greatly appreciated.

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UPDATE: 

I installed the Applied Racing smog block off kit, which completely eliminated my backfiring issues. I did some adjusting to my fuel screw, and it is currently 1 1/2 turns out. With it like this, when I pull the hot start slightly the bike revs up, and when I pull it all the way in the bike dies. Pulling the choke out still does not kill the engine though. I am also still having some troubles with the stalling off idle and idle speed changing. 

  • When I first warm the bike up and start the ride my hour meter will say the RPMs are between 1750-1820, just watching the meter while the bike is idling you can watch the RPMs rise and fall slightly without the throttle being twisted. When I ride for a few minutes and come to a stop, the meter will be reading lower, 1700-1720, or higher, 1850-1900, than what it was before I started riding. The meter could possibly be off, but when I do come to a stop sometimes I can tell that the bike is idling lower or higher than normal just based on the sound. 
  • The bike still seems to stall off idle, but there doesn't seem to be a pattern to the stalling. Sometimes I can have the bike on the stand idling, give it a twist and it revs up fine, then the bike will stall and die before I even open up the throttle on the next twist. The same thing happens when I am out riding and I come to a stop. I can rev the bike up on the first few twists of the throttle, and then on the next twist the engine will just die. The throttle is hardly twisted when the engine dies. Also, on some occasions there is a clank noise that happens when the bike stalls, but doesn't happen all the time. Sometimes the bike stalls quietly, and other times it stalls with a clank that is loud enough to be audible. This bike only has 8-10 hours on it since buying it from a dealer so I wouldn't think anything engine wise would be going on.

I did happen to notice one thing with my R&D racing fuel screw. The needle tip of the stock fuel screw seems to be longer than the needle tip of the aftermarket screw. I have not compared both to see if one screw is actually longer than the other. I may install the stock screw to see if there is any change in performance. I am honestly stumped on what could be causing this problem. The only things I changed on this bike were the main jet from a 130 to a 158, the red needle with the clip in the 5th position, the air box mod, and the aftermarket fuel screw. I did remove the stock pilot jet from the bike and replace it with the one from the JD jetting kit, but both pilot jets were size 42. I know the fuel screw and pilot jet impact the slow circuit, and I am not sure if I should try changing to a different size pilot jet, or changing fuel screws. 

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All your fuel screws should be the same length and shape. The cheap aluminum screws have been known to deform or break at their tips. If your Tusk screw is shorter, you may have a broken tip, which may be lodged in the carburetor. Brass is the way to go.

If the bike won't die with the choke on, it means you aren't able to make it too rich. This would indicate a lean idle/pilot circuit. I'd remove your fuel screw and make sure there are no problems or obstructions like broken fuel screw tips or an extra or missing o'ring. Then I'd reassembe with the R&D flexjet and perform Jim's tuning procedure. You haven't made any mention that you've done his procedure, and the flexjet makes it easy.

Your bike has the upgraded Accelerator Pump. My bike is the same as yours and with the JD kit and properly tuned (flexjet) pilot circuit it has no bog. Yours should run the same.

Good luck!

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I did attempt to do Jim's tuning procedure, and that's where I ended up at 1 1/2 turns out. One thing I didn't think about until now is the order of the spring, washer, and o-ring on the fuel screw. The order on mine is washer, spring, then o-ring, instead of spring, washer, o-ring. I noticed yesterday that this was the order, but it never dawned on me that this was the wrong order until I was reading another forum on TT about the fuel screw. I'll remove the fuel screw and put the components back in the proper order, and then retry the tuning process. 

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Get the order correct on the fuel screw and this may take care of the bog off idle.

If it does not, then you need to start looking else where and not mess with the slow circuit.   You don't want to change anything there.    FWIW, a #42 and 1 1/2 turns out is pretty standard  and the setup of these bikes is well known at this point.  You might need to go a little richer on the fuel screw, but your running at a slightly higher altitude and with warm temps, so 1 1/2 is not out of the question (usually 1 3/4 is pretty spot on).

For the bog, you need to differentiate between rolling the throttle on and a quick twist.   I would suggest riding on some level trail and slowly rolling the throttle on to determine if it bogs or not.    If it does, then move the clip to the 4th slot on the needle and test again.    If it does not, then move onto quick twists.   If it now bogs, then you need to go one or two sizes smaller on the leak jet.  

This jet is the opposite of a normal jet; smaller = more gas for the AP to squirt. How this works is that the AP bowl fills with gas and when you open the throttle quickly, the diaphragm squeezes the gas in the AP bowl, which makes it squirt into the carb throat.  There is also a second passage back into the main bowl allowing gas to "leak" back into it.  This is what the leak jet controls.   So smaller prevents less gas from leaking back, and a larger jet would allow more to leak back giving less gas for the AP to squirt into the motor.

The leak jet is in the bottom of the float bowl and you must take it off to change it.

I would not worry about the choke circuit until you get everything else set.

Jim.

Edited by Jim Dettman

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My parts finally came in...

R&D screw didn't fix the bog.

Changed the needle clip position from 5 to 4th position and the bog disappeared while testing it out in the garage tonight.

Taking the bike out this weekend, I'll post an update post ride!

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Rode Saturday and Monday, 10 hours in total, long story short I think my bog issue is rider related.

I noticed that my first throttle snap is always fine, no bog...but subsequent snaps would kill the engine, by the 2nd or 3rd snap, dead. The first 20min. of riding on Sat. I killed it at least 15 times. My buddy picked up on how much throttle snapping I was doing while riding. He was like "why you snapping it so much, it's a 4 stroke, just feather the clutch and keep your throttle steady", I owned a 2 stroke when I was young, explains the habit. So, I made it a focus all weekend to stop snapping my throttle unnecessarily and my self-created bog vanished.

Today, I called JD to share what I discovered. R&D fuel screw didn't fix it, needle in 4th position made the idling a bit more choppy, but my bog didn't go away. I explained how I thought it could be my riding style, and right away he confirmed that was most likely causing the issue. He too did the move from a 2 stroke to a 4 stroke and had the exact same issue. So I asked him to explain how the bog wasn't present before the JD changes, he explained that since these bikes come so lean out of the gate my throttle snapping never flooded it with fuel, the bike just liked it as he put it. Since the JD changes the bike is now properly jetted, It gets way too much fuel when I snap my throttle repeatedly and eventually kill it.

He recommended I actually go up on my leak jet to a 70 if I can't kill my old throttle habit, this would stop the rich effect I'm causing with the snapping.

I'll relearn how to control my throttle for now, and go up on the leak jet later if needed.

Thanks again for all the assistance and insight!

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If that bike had gas in it in 2015, and sat at the dealer for 2 years, then the fuel screw passage is probably plugged.

Set the fuel screw at 1 7/8 turn out and never touch it again. Don't make a simple thing difficult. The fuel screw helps with starting and idle, and you are on the right track with the needle clip being richened up. Your bog is a lean spot going from the pilot circuit to the mid range. The 2006 model was the worst for this, and it was a lean needle.

if you ever put a 205 R cam in it, go to a 45 pilot.

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On 7/21/2017 at 8:42 AM, Jim Dettman said:

post-231688-0-92062800-1363528365_thumb.jpg

 

 Carb tuning is done from the top down, staring with the main jet, then moving onto the needle, it's taper, clip position (height), and diameter.   Slow circuit is done by itself last as well as the choke circuit.

 Also, you should not be expecting anywhere near the same mileage after the re-jet as before.   

Out of Curiosity, what kind of mileage can you expect after basic mode like jets, needle & airbox?  I get about 100km on the norm, would it drop significantly?

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