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2010 EXC 250
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Discussion Starter · #1 ·
Hi guys,

Had a search and a bit of read of various other threads but I'm still a bit unsure of what to do first

I have a 2010 EXC250, it runs perfect apart from when I slowly pull away in first. I would describe it as a slight hesitation or stutter just before the power valve opens. If I wind the throttle open quickly it pulls beautifully. I think it might be the fueling but unsure what to try first.

I've checked the power valve operation and it seems to be working as expected, it's running the yellow spring with the brass adjuster just under flush with the case.

I've pulled the carb to give it a full strip and clean and my specs are

Needle is N8RW - second clip from bottom
Main jet 165
Idle jet 35
Starter jet 85
Air mixture screw 1.5 turns out

Im not sure what to start swapping first.

On Sunday I done 107 miles Green lanning and was getting 25-26mpg with a fair bit of fast flowing lanes and a decent bit of fast road work, I do get a bit of splurge from the exhaust but not excessive, I run Motorex synthetic blend 2T @ 50:1 and it had a brand new air filter before the last ride, I did have to fill up with E10 95 Ron when out as that all they had, if its relevant.

Thanks.
 

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Put that needle in clip 3. It’s in 4 now which unless you are pretty much giving it some then the rich stutter you are getting will be there. Clip three should clean it up.

Try 60-1 as well. I was talking to a mate the other day about this. We both got spooge running 40 and 50-1 (less at 50) on 150s that are supposed to like the higher oil amount. Trouble is the excess oil migrates through the pipe and you’ll get a dribble. On 60-1 there’s no spooge. A tub of 150 pistons all look the same after various oil amounts so it makes no sense to use more oil than required. My Beta is on 60-1. No spooge. Modern oil is very good. Have faith!
 

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as pindie said lean the needle one notch and try again.
always keep to whatever ratio it's been jetted for.
chap at the track over the weekend seized his bike due to this. had 60:1 fuel for his ktm and some 32:1 mixed ready for his Rm.
ran out of 60:1 so stuck the 32:1 in the ktm and it seized within 2 laps.
without the extra petrol keeping the piston cool it overheated and nipped up solid
 

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I must not mention my favourite needle 8-]
Funnily enough, I just re-read the mammoth thread about "that" needle. I put it in as I needed to improve the fuel consumption and take the massive low end hit away. It certainly did both things perfectly. Going to lower the clip to try and make it a bit beefier but am going to give it another go after quite some time on the N8RG needle.

Being able to change the engine character of a bike massively in 10 mins is really useful.


As for the OP, I'd consider going to a 38 pilot too. It might even out the transition a bit.
 

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I just spent ages trying to explain to someone locally how if you change needles, you also need to change other parameters to ensure everything keeps working in harmony. He’d wanted more torque and hit. I lent him the needle that’d do it in his 300. However, he wasn’t prepared to try other clip positions so went back to what he originally had and didn’t like. 🙈

You can lead a horse to water……

It’s always worth fiddling. It might seem a pain but it’s the only way to find out. You’ll always find out when you’ve gone the wrong way.
 

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It's definitely worth sacrificing a day to try a wide range of jetting so you can feel what each bit does and what lean and rich feel and sound like. I'm no expert but I know enough to make a difference where I want it.

But then it's a dying art... A few more years and it'll be a phone app that you can use to change the fuelling as you want. Which to be fair would be very cool.
 

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On a 250, l would go 38/40 pilot, 168 main and the NECJ at 3. Airscrew to suit the day. Damn - l said it ;-)
 

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gotta love that NECJ needle! all my off road bikes run one. 250, 300 and 500! hope they never stop making them.
 

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It's definitely worth sacrificing a day to try a wide range of jetting so you can feel what each bit does and what lean and rich feel and sound like. I'm no expert but I know enough to make a difference where I want it.

But then it's a dying art... A few more years and it'll be a phone app that you can use to change the fuelling as you want. Which to be fair would be very cool.
YZF has had that for a few years already. It's bloody good!
 

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Do you not find NECJ a tad lame? To me it always feel perfectly clean and linear but the bike feels flat.

I’m using the needle I liked the most in my 200. NEDW. That in clip 4 in the Beta is really nice. Lots of instant torque and good fun. Makes the sort of power delivery that allows uphill wheelies over logs/ledges without spinning or not lifting. Probably not a trail/road ride needle though.
 

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I think the smaller bikes like the richer needle pindie.
I've used the NEDW which it will still run clean in the 300 and 500 however i get that annoying 4 stroking in deceleration.
nice way of making a NECJ feel wild is adjusting the fuelling with the slide.
going from a stock 6.5 to a 7 perks it up a lot without being lean.
using a beta 7.5 slide its mental off the bottom end and a 8 slide will try and kill you until the bike seizes (tad too lean)
 

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Yep, the necj makes the 300 feel like a 275. It's still got more bottom end pull than a 250 but doesn't have that instant urgency off a closed throttle that comes with the N8RG. In 2nd gear, even with a slower throttle, it's hard (for me) to really control that amount of grunt if I'm trying to ride aggressively. The NECJ does feel a bit flat up top but then how many people can ride a 300 on the pipe anyway.

For me, doing an event where saving energy and staying smooth was key, it was perfect. But if/when I want something more aggressive then the N8RG/H will go back in.

I'm constantly toying with swapping back to a 250 as they are definitely easier to ride hard, but then I'll do some mega technical stuff and think there's no way I'm swapping the 300.

I'm going to play around with the NECJ and see if I can wake it up a bit.

Mind you, my front pipe is fucked so that is killing the top end anyway.
 

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Couldn’t control my fiddling fingers so had a rustle about in the jetting pot and found an NOZG needle. Popped it in. Been for a woods ride. Even nicer again. More urgent and super smooth. It might be a thirsty needle though so will need to keep an eye on the but the G is working well.
 

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have you tried a leaner slide? I can lend you one if youd like to try it.
Is that for me? If so, thanks that's a great offer but I'm going to lower the clip and see if that works. No idea what a leaner slide will do but I'm happy enoughish with having two settings - one mild, one wild.
 

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Couldn’t control my fiddling fingers so had a rustle about in the jetting pot and found an NOZG needle. Popped it in. Been for a woods ride. Even nicer again. More urgent and super smooth. It might be a thirsty needle though so will need to keep an eye on the but the G is working well.
You just couldn't leave well enough alone... 🤣😂🤣

I'd definitely play about if I could go riding whenever I fancied it. But if I've got a setting that works pretty well for everything then I don't worry if it's a little off here and there. I could do with somewhere to really dial in the main though.
 

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Weston beach race is coming soon!!!

What main you got in there now?
 

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2010 EXC 250
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Discussion Starter · #20 ·
Right... I fully stripped and cleaned the carb and moved the clip position as suggested, it has improved the hesitation but it was an absolute [email protected] to start the first time after putting it back together. Does needle position change how easy a bike will start? Done a cold start the following day and it fired up on the 3 kick but only without choke, have I cocked something up on reassembly?
 
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