How to know if the bike is running lean?

[GGRider01]

Let's take a step back here. Did you set the float level on your carb again? So it doesn't spill while on the side stand?

There are two AirStryker carbs, the AS1 and AS2 and they both have drastically different float level specifications.

Identify the AS1 by a large screw on top. Just set the floats so the seams left by injection molding is parallel to the carb body. About 16mm
The AS2 has two philips holding a rectangular cap on. I believe this one is about 6.5mm.

Once that's sorted, move on to the needle. I am utterly convinced that since you got the bike with a 172 and had sputtering issues that it has to be the needle. It was the only rich circuit in your carb unless your humidity is 99.9% and the temperature is 30C and everything around you is dying of oxygen deprivation.

Keep raising the clip position until you get to #1.. if that doesn't fix it, then start dropping sizes on the main jet. Just reset your needle to #3 every time you change main jet and start the process over. This is 99% of jetting.

[Munch]

Originally Posted by GGRider01

Let's take a step back here. Did you set the float level on your carb again? So it doesn't spill while on the side stand?

There are two AirStryker carbs, the AS1 and AS2 and they both have drastically different float level specifications.

Identify the AS1 by a large screw on top. Just set the floats so the seams left by injection molding is parallel to the carb body. About 16mm
The AS2 has two philips holding a rectangular cap on. I believe this one is about 6.5mm.

Once that's sorted, move on to the needle. I am utterly convinced that since you got the bike with a 172 and had sputtering issues that it has to be the needle. It was the only rich circuit in your carb unless your humidity is 99.9% and the temperature is 30C and everything around you is dying of oxygen deprivation.

Keep raising the clip position until you get to #1.. if that doesn't fix it, then start dropping sizes on the main jet. Just reset your needle to #3 every time you change main jet and start the process over. This is 99% of jetting.

The bike occasionally does spill out fuel if the bike is on it's stand but not always, I don't know why. Maybe the angle of how far down it is on the stand?

I have tried to set the float but it is so confusing and I can't seem to get it correct, I believe I have the AS1 carb I think because the throttle assembly comes out of the top by twisting the cap and not by screws. I don't understand what you mean by your instructions, do you have a pic of how the float should sit? Is it worth trying to set it tomorrow before testing the bike?

[GGRider01]

You can see a seam on the floats from the manufacturing process. Notice how the seam is parallel to the carb body? Sounds like you have the AS1 (which is the one pictured here). I'd make sure it's set correctly. If the bike runs good enough to race it, I reckon it could wait, but float setting is the absolute #1 step in jetting.

Anyway, I don't think you're too lean. I think your plug wasn't very dark because it didn't get used for very long.

[Munch]

Originally Posted by GGRider01

You can see a seam on the floats from the manufacturing process. Notice how the seam is parallel to the carb body? Sounds like you have the AS1 (which is the one pictured here). I'd make sure it's set correctly. If the bike runs good enough to race it, I reckon it could wait, but float setting is the absolute #1 step in jetting.

Anyway, I don't think you're too lean. I think your plug wasn't very dark because it didn't get used for very long.

Just to make sure I am understanding this correctly, do I make sure these lines are matching(red line):


Will setting this make a difference to the problem I'm having? I have come from a kx 125 so I am OK with the power right now, I am never wanting/needing the powerband so I can ride how it is and I don't want to pull the carb out of the bike (pain in the ass) if it's not going to help my issue specifically tomorrow however I will of course set it during the week after tomorrows ride.

[Jakobi]

Originally Posted by GGRider01

Let's take a step back here. Did you set the float level on your carb again? So it doesn't spill while on the side stand?

There are two AirStryker carbs, the AS1 and AS2 and they both have drastically different float level specifications.

Identify the AS1 by a large screw on top. Just set the floats so the seams left by injection molding is parallel to the carb body. About 16mm
The AS2 has two philips holding a rectangular cap on. I believe this one is about 6.5mm.

Once that's sorted, move on to the needle. I am utterly convinced that since you got the bike with a 172 and had sputtering issues that it has to be the needle. It was the only rich circuit in your carb unless your humidity is 99.9% and the temperature is 30C and everything around you is dying of oxygen deprivation.

Keep raising the clip position until you get to #1.. if that doesn't fix it, then start dropping sizes on the main jet. Just reset your needle to #3 every time you change main jet and start the process over. This is 99% of jetting.

Humid and hot - they are my typical conditions here

The video of the CR shows a definite rich condition, and the comments confirm; his main jet had backed itself out and was in the bottom of the bowl. The sound is less of a bog/hesitation and a wet blubbering sound.

While I don't agree with tuning a bike on a stand this video/APT review on a YZ shows what a lean hesitation sounds like. https://www.youtube.com/watch?v=0AKXLEmAVEs - it is a very different starving sound, rather than the engine blubbering and not taking revs cleanly. See 4:35 for the lean bog.

And another by slavens.. See 3:59 for a lean bog off the idle circuit. https://www.youtube.com/watch?v=zVzqqpgviyI

As you can see you can be rich and lean in different places. The OEM N1EF has a very short straight section which means that almost as soon as the throttle turns you are overlapping the first taper and pilot circuit. The first taper is very rich and as such many end up either dropping the pilot very small to compensate, and/or raising the clip up to try and clear the off idle area. If you keep lifting the needle to clean up the bottom end you'll end up lean in the mid range. If you try to address it with a small main you end up lean up top. And to add to all of that, being rich off the bottom means any time you putter around the engine loads up.. You then need a couple of hard runs before it will pull clean, and in that time it will blubber until it clears out.

Had the same issues with my own bike when I bought it. A different needle is the right place to start, however which one you choose to go with will be a personal choice.

In realtion to the float height, it's the first place to start. If the bike leaks on the stand intermittently consider replacing the Viton tipped needle valve. They can perish and cause similar issues. Also, if it's an old carb the actual nozzle where the needle interfaces can become worn and will put you around in circles for a long time.

[Munch]

Ah ok thanks that clears it up for me, hearing them bikes that are lean I think I am confident in saying my bike is not lean as I'm not getting them types of sounds.

[GGRider01]

If you keep lifting the needle to clean up the bottom end you'll end up lean in the mid range. If you try to address it with a small main you end up lean up top

Munch, that is a huge caveat to my rudimentary methods and probably how the 172 got in that bike to begin with. Listen to Jakobi

I still firmly believe you can get the N1EF to run "good" (highly subjective). I bet you #2 on the needle will get you results, at least temporarily, until you start trying new needles. I'm going to go out on a limb and suggest the N3EG to start with.

[barossi73]

Im going to chip in and reinforce 2 things.
1.float level is critical,if its too far out other changes will not cure problem,although there may be some improvement.based on fuel spilling you need to lower float/fuel level (assuming viton ok)bear in mind the carb will be upside down when you adjust.
you are setting to the point where the spring loaded pin in viton is only just fully compressed (from memory,its been awhile)
2.if you are trying to read plugs an old plug will change color quickly.a new one wont until it has some hours on it.point is if you go too lean you want to know sooner not after hours of lean running.also if you change float level either way,the altered mixture may change plug appearance.float level first

[Munch]

Would it be worth me trying to get something like the JD jetting kit?

I am looking for it in the UK but can't seem to find anything. Is there anything similar in the UK?

[Jakobi]

You've been given much advice munch. No one will really be able to recommend you a needle because you haven't confirmed any details such as:

Model of carb (AS1 or 2) - Suspect AS1 given its an 06 250.
Slide number (and if it has a notch cut in it).
Have you set the float height? The magic number depends on the model of carb. See above.
The fuel overflow issue - have you determined if it is the float height or the Viton tipped needle valve? You won't have success if the engine is intermittently flooding itself.
Your temperature, elevation, fuel quality (RON?, ethanol blend, etc).
Mechanical history? Have you taken any comp readings? Done any leak down tests? You won't be able to jet around a mechanical issue.
Which leads us to squish clearance too. You can spend a lot of time jetting in circles if the head to piston clearance is excessive (as some stock setups have been).

And after all that, Capz gave you some advice back on page 1 "I used to run a 45pj and 180 main with one of the N3 series"

That's where I would start too. 45 N3EG#3 180 probably.. depending a whole lot on the answer to the multiple questions above.

KTM part number: 54731134000 ..available through whichever source you please, at probably a load of difference price points.

Main point to note is that it is the whole package working together. The whole carb needs to be in good order. The whole engine too. Be methodical and precise in how you approach it, and you'll end up gaining a wealth of knowledge and a bike that runs just the way you want it to.