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200 EXC mid-range surging?

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Hey guys

 

I've put some hours on the 200 of mine now, and I'd like to work out the kinks it's had from when I got it. One of which is this awful mid rpm surging. It usually happens RIGHT before the bike gets on the pipe. It's like the bike gets "in" the pipe, then goes back out and then revs again because it goes back on the pipe. Idles great. Revs great and it smooths right out when I get on the throttle.

 

My initial thought was maybe messing with the main jet. I'd like some input on what I could do to get this bike to go through the revs smoothly, rather than jerking around before I get in the powerband.

 

This issue doesn't when I'm lugging around or if I'm in a high gear and lay on the throttle (from low to high rpms). 

 

Any ideas that can be bounced around are appreciated!

 

Thanks!

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I had the same issue with my 2013 300xc. Jeff Slavens suggested I try running straight race fuel. If that worked we would dilute it down with pump gas as far as we could.

It worked. The bike runs so good now on 100% VP C12. I'm going to use the whole 5 gallons at 100% to clean things out and then try VP 110 from the pump. I just found a place that sells it for $8.80/gl. The C12 from my local dealer is $85 for 5 gallons or $17/gl.

If it runs just as good on 100% VP 110 from the pump I'll start mixing it weaker and weaker until I find the perfect ratio.

So my suggestion to you is run race gas and if it works, thin it down until you find that perfect ratio.

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I honestly don't know whatt's been done to the carburetor, if anything. For all I know (until I dig into the carb) it could have NOTHING stock in there. At which point, I may as well go stock and work from there?

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no, stock is not good, the needle needs to be changed if you want it to run the best it can, match the jets to the new needle

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I'm running 50:1

 

What is the rule of thumb when changing needles? What should I look for?

Before messing with different needles, start messing with needle position. If that doesn't work, it isn't like you spent money to find out. 

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Before messing with different needles, start messing with needle position. If that doesn't work, it isn't like you spent money to find out. 

I work on small engine carbs all the time, but this concept of needle position is something I must not know much about.

 

I think my manual had a section about it though, or maybe that was just float position?

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I work on small engine carbs all the time, but this concept of needle position is something I must not know much about.

 

I think my manual had a section about it though, or maybe that was just float position?

An easy way to think about the three main circuits of a carburetor: Pilot (idle to about 1/3 throttle) needle (1/3 throttle to about 2/3 throttle) and main jet (2/3 throttle to open). Also, all the circuits will overlap each other, and so on. The needle will generally have about 5-6 notches in them, with them going leaner to richer from top to bottom.

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An easy way to think about the three main circuits of a carburetor: Pilot (idle to about 1/3 throttle) needle (1/3 throttle to about 2/3 throttle) and main jet (2/3 throttle to open). Also, all the circuits will overlap each other, and so on. The needle will generally have about 5-6 notches in them, with them going leaner to richer from top to bottom.

So, what is it my needle is doing wrong? Is it not opening the proper amount to let fuel in (causing the lean condition and surging?)

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stock KTM needles are triple taper. Almost all of them are too rich on the bottom and then surge into the midrange with a too big burst of power for smooth trail riding. Go to a single taper needle to smooth it out and make it more manageable. With a single taper needle you will then need to go to a larger main due to the overlap as explained above. Check the 200 thread in this forum for more or exacts.

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I'll keep what's been said in mind. I'll have to tear into the carb maybe after labor day weekend (don't see it happening this week).

 

Then the fun begins. What's in there right now? Stock? Something else? Couldn't tell ya yet haha

 

Thanks, more suggestions welcome though

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To possibly help with the surging, should the clip position be moved up or down? I've read that moving up makes the bike leaner and down makes it richer. By that logic, I'd want to move the clip down correct? Unless of course the surging isn't lean-surging...

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To possibly help with the surging, should the clip position be moved up or down? I've read that moving up makes the bike leaner and down makes it richer. By that logic, I'd want to move the clip down correct? Unless of course the surging isn't lean-surging...

People often struggle when discussing the needle position, up and down with the needle and the clip position are actually inverse to each other. So yes, if you move the clip to a lower position on the needle it will in fact raise the needle and make the jetting a tad richer at most all throttle positions with the exception of WOT.

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Wow, I went through a litany of jetting on my former 2002 KTM 20EXC.  I do recall that in all the experimenting I did, one of the things I did was dropping from a 42 to a 40 pilot jet.  I think that had the single biggest impact at the time.  I experimented with countless needles and never got it exactly dialed to my complete liking...but the closest came with the 40PJ.  I ended up experimenting past my "personal best" settings and it ran a little worse, but I ended up selling it at that point before getting it back where it had been at its best---new owner liked it just fine, and I may have been a bit too picky.  So when I did have it dialed in at its best for me, it always felt sort of thin in that spot just above idle, or cruising range.  But despite feeling that way, it had absolutely no surging, and it never fried the top end nor overheated at all, and it transitioned to full throttle without any blubbering or hesitation.

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People often struggle when discussing the needle position, up and down with the needle and the clip position are actually inverse to each other. So yes, if you move the clip to a lower position on the needle it will in fact raise the needle and make the jetting a tad richer at most all throttle positions with the exception of WOT.

Wouldn't that mean I should go leaner on the pilot and main to compensate? Or is it either/or?

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Wouldn't that mean I should go leaner on the pilot and main to compensate? Or is it either/or?

One change at a time and no you don't want to change the others because you changed the needle.
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come on squid tell him the secret jetting specs, wasn't it ddk 40 180?  seriously though buy a few needles and pilots and mains and start playing keep in mind all bikes do not require the same jets. after reading the jetting section and paying attention to what others in your area are running buy some stuff and have fun.

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come on squid tell him the secret jetting specs, wasn't it ddk 40 180?  seriously though buy a few needles and pilots and mains and start playing keep in mind all bikes do not require the same jets. after reading the jetting section and paying attention to what others in your area are running buy some stuff and have fun.

Depends on his year but if it's an 01 and stock and I put in a JD Blue, 188 main and a 40 pilot. If it's a 39mm carby then 195 main, 45 pilot same neelde. 

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