2007 YZ 250 jetting question

[bronc3]

I have a stock 07 YZ250 that has a stutter at light throttle just getting into midrange rpm. Can this be smoothed out? I use the bike mostly for woods riding, often riding a gear high.

I don't have any fouling issues, but do get a fair amount of spooge from the silencer. I am running stock jetting with the exception of 1 size down on the pilot and the needle lowered one notch, riding primarily at sea level. The bike is stock except for the FMF S/A silencer I run for public lands and hare scrambles. Exhibits the same symptoms with the stock silencer.

I am using Motul 800 synthetic @ 32:1. Bike runs very strong overall as is.


Thanks for any help you can provide.

[chud]

Have you tried leaning the pilot w/ an air screw adjustment?

[YZhallsme]

Originally Posted by bronc3

I have a stock 07 YZ250 that has a stutter at light throttle just getting into midrange rpm. Can this be smoothed out? I use the bike mostly for woods riding, often riding a gear high

I had a similar problem with my 03', it took a little experimenting with jetting to find a solution. My stutter would occur between closed and 1/4 throttle, is this the same throttle position that your problem occurs? As chud suggests you should try your airscrew first. Stutter is usually an indication of being rich while a bog is usually associated with being lean. I'd suggest indexing your throttle, it's simple and provides an easy way for you to determine at what throttle position your problem occurs. It's important because jetting is throttle position sensitive.

[bronc3]

Originally Posted by YZhallsme

I had a similar problem with my 03', it took a little experimenting with jetting to find a solution. My stutter would occur between closed and 1/4 throttle, is this the same throttle position that your problem occurs? As chud suggests you should try your airscrew first. Stutter is usually an indication of being rich while a bog is usually associated with being lean. I'd suggest indexing your throttle, it's simple and provides an easy way for you to determine at what throttle position your problem occurs. It's important because jetting is throttle position sensitive.

Sorry, I've been away for a few days.

You are describing my problem pretty much exactly. I'll try leaning out the pilot a bit and see if it changes. all indications are that the bike is a bit rich at lower RPM, I just didn't know if the stutter could be eliminated or if it was just a charcteristic that I have to live with. The bike is quite ridable as is, but would be better if I can eliminate the stutter.

[YZhallsme]

Originally Posted by bronc3

Sorry, I've been away for a few days.

You are describing my problem pretty much exactly. I'll try leaning out the pilot a bit and see if it changes. all indications are that the bike is a bit rich at lower RPM, I just didn't know if the stutter could be eliminated or if it was just a charcteristic that I have to live with. The bike is quite ridable as is, but would be better if I can eliminate the stutter.

I agree, the bike was very rideable with the stutter. However it's my opinion that it's much better without it, plus it doesn't show much in the way of spooge now. I think it's possible that you can reduce, if not eliminate the stutter too, but your bike is newer than mine and your riding conditions are different. I have a few idea's from my own experience with the 03' that might help, however you should know that I'm no jetting expert. Also I'm totally unaware of your jetting knowledge, if anything I post seems demeaning in any way, I apologize as thats not my intent. Ok then starting with the pilot circuit, do you understand how it works? that the airscrew and pilot jet work in conjuction with one another? that you can determine if you have the correct size pilot by using the airscrew? Also it would be helpfull to know for sure whats in your carb, from your post and my limited knowledge of the 07' I'd guess currently your at a 178 main, 48 pilot, needle N3EW in clip position #1(top groove), is this correct?

[yathump]

The stock jetting on the 07 is a 50pilot-N3EW needle 2nd clip and a 178 main

Where is you're airscrew set at, try turning that out if the throttle response gets better aswell as the spooge and you're at 21/2turns out or more you still need a leaner pilot. If you find that the needle is to rich you could try the N3EJ as it is leaner

[bronc3]

I am one step down on the pilot now, with the screw around 2 1/4, stock needle with the clip in the second groove down from the top, stock main. I was considering the next leaner needle, but it is probably in the pilot. Bike runs excellent, with the exception of the slight stutter at light throttle and also minor spooge.

I had also considered dropping the needle to the last groove, but wouldn't it be better to switch to the next leaner needle starting in the center groove?

[yathump]

I'd try a 45 pilot and readjust the airscrew

The spooge factor might always be there if you're not creating high enough combustion temps to burn it off, depending on your rideing style you might always have some, i normally end up with a slight mist around the outlet of my exhuast after running single track here in MI at 1/4 to 1/2 throttle

[bronc3]

I am pretty sure it is a 45 or 47.5 pilot in it now, I'll check my records. As for slight spooge, I agree it could be my riding style as I use the bike for woods riding quite a bit riding a gear high, but even at the track I get some drool out of the pipe.

[yathump]

If you're 1 step leaner than stock it should be a 48, if you want you could try the N3EJ needle which is slightly leaner, the N3EJ came stock on my 06 but they switched to the N3EW in 07 trying to eliminate the pinging that was was going on. I personally never had any issues with it but there were many that did but choose to run a mix of pump and race fuel in stead of switching needles

[YZhallsme]

Ok your original post confused me as you said "needle lowered 1 notch", from stock this would have put you on clip position #1 (top). But now I see your on clip #2, this makes more since. I couldn't resolve the stutter with pilots, my guess is you might not either, still the pilot/airscrew is were you want to start. Check the sticky at the top of the page, I think it explains just how to determine if you have the correct size pilot.

I am one step down on the pilot now, with the screw around 2 1/4, stock needle with the clip in the second groove down from the top, stock main. I was considering the next leaner needle, but it is probably in the pilot. Bike runs excellent, with the exception of the slight stutter at light throttle and also minor spooge.

I had also considered dropping the needle to the last groove, but wouldn't it be better to switch to the next leaner needle starting in the center groove?

I would work with what I have to begin with, a little experimenting with it might help to determine which needle you'd like to try next. If the pilot/airscrew doesn't work then try clip#1 but be aware that sometimes a move to a leaner clip position requires a richer pilot. Note:when you change clip position, be prepared for a much more noticeable change in how your bike responds, good or bad.

I am pretty sure it is a 45 or 47.5 pilot in it now, I'll check my records. As for slight spooge, I agree it could be my riding style as I use the bike for woods riding quite a bit riding a gear high, but even at the track I get some drool out of the pipe.

I'm fairly confident that as you reduce/eliminate the sputter you'll see less spooge, track or trail!!

[bronc3]

Sorry, I thought the middle groove (clip #3) was the stock position for the needle clip. I found it on clip #2 when I pulled the carb to change the pilot. I thought my mechanic friend at the dealer repositioned the clip for me when he prepped the new bike for me, but I guess that's not the case. Is it a bad idea to try the clip at the top groove, or should I order the next leaner needle and start in the center groove?

I will probably pick up the next leaner pilot and try that also, but want to make one change at a time and test.

I wasn't sure of the increments of the pilots for this bike; the last bike I jetted was my DRZ and they come in 2.5 increments.

[YZhallsme]

Originally Posted by bronc3

Sorry, Is it a bad idea to try the clip at the top groove, or should I order the next leaner needle and start in the center groove?

I will probably pick up the next leaner pilot and try that also, but want to make one change at a time and test.

I wasn't sure of the increments of the pilots for this bike; the last bike I jetted was my DRZ and they come in 2.5 increments.

No, it's not a bad idea to try clip#1, it may run bad or it may run awesome you just won't know untill you try! Again if nothing else it could help you to determine which needle to go with. You say the next leaner needle but do you realize you actually have a couple choices here? Yamaha offers one that is one step leaner on the straight diameter and one that is a step leaner in regards to taper starting point or shall we say clip position. I think both would have a positive affect in regards to your stutter issue. N3EJ is the next leaner straight diameter, a straight diameter change will affect closed to 1/4 throttle, most notible at 1/8. N3CW is 1/2 clip position leaner than N3EW. So then, N3CW in clip position #2 would be the same as your N3EW in clip position #1.5, that is if you could put it there. A clip position change will have a much broader affect, say from closed to wide open throttle, most notible at @ 1/4. You may not think that 1/2 clip would make a difference but it can! You say after 1/4 it runs "excellent" but does it really? is it possible it could be even better? I say "you won't know untill you try" but a prominent suspension tuner say's it best when he say's; "the best you know is the best you've rode"! I agree on "one thig at a time", and when you test pay close attention to what the motor is telling you. As for the pilots, from your stock size down 50,48,45,42,40,38,35. You really should try indexing your throttle, here's an easy method. All you need is a felt tip marker (sharpie) in a color that will show easily on your throttle grip and housing. Start with a mark on the outer edge of the throttle grip flange at @ 12 oclock, then twist the throttle just enough to eliminate the cable free play. At this point put a corresponding mark on the throttle housing this represents closed throttle. Twist to wide open and put a second mark on the housing (full throttle). Split the distance between these two marks with a third mark which represents 1/2 throttle. Do the same for 1/4 and 3/4 throttle. You now have an easy way to more precisely identify the throttle position.

[bronc3]

Again, thanks man. I do understand that the needles are different by a "half groove", and do understand the difference in profiles. Sounds like the N3EJ might be the ticket as my issue is around 1/8 throttle. I opened the airscrew 1/4 turn and it seems to have helped, but I haven't had a chance to really ride the bike since I made the adjustment. This puts my airscrew around 2 3/4 turns.

I will probably order the N3EJ needle just for good measure.

[KKXR400R]

I bet the flaming session is going to commence but 32:1 with a quality synthetic oil is a waste. I bet that sounds harsh but you could seriously save yourself quite a bit of $ by going with 44:1 or 50:1. I hate solving jetting issue by changing pre-mix ratios but you may want to give it a shot.

I know alot of people are helping you but I'll throw something out here for you. Your needle sounds a little rich too me. Let me guess:it kinda stutters right before it gets to the mid range hit? had the same problem. Leaned out the needle and problem solved. The difference is I run 50:1 on all my bikes. I seriously doubt your going to need to order that needle.

-Kevin-

[bronc3]

Thanks, I've read about 32:1 not being needed, but I've also read good evals after engine teardown when running Motul 800 @ 32:1. I have been considering mixing at a leaner ratio, but that will probably require a complete rejet due to the richer fuel mixture.

[bronc3]

I was amazed at how well adjusting the airscrew cleaned up the light throttle.

[yathump]

Originally Posted by KKXR400R

I bet the flaming session is going to commence but 32:1 with a quality synthetic oil is a waste. I bet that sounds harsh but you could seriously save yourself quite a bit of $ by going with 44:1 or 50:1. I hate solving jetting issue by changing pre-mix ratios but you may want to give it a shot.

I know alot of people are helping you but I'll throw something out here for you. Your needle sounds a little rich too me. Let me guess:it kinda stutters right before it gets to the mid range hit? had the same problem. Leaned out the needle and problem solved. The difference is I run 50:1 on all my bikes. I seriously doubt your going to need to order that needle.

-Kevin-

Did you notice that you had to lean out your jetting to compensate for the richer air/fuel ratio

[YZhallsme]

Originally Posted by bronc3

Thanks, I've read about 32:1 not being needed, but I've also read good evals after engine teardown when running Motul 800 @ 32:1. I have been considering mixing at a leaner ratio, but that will probably require a complete rejet due to the richer fuel mixture.

Something to think about, a change from 32:1 to 50:1 = @ 1% more fuel across the throttle range. A change from a 48 to 50 pilot = @ 5% more fuel at idle then tapers down to less than 1% at 1/4 throttle. A main change from a 178 to 180 = a gradual increase in fuel starting @ 1/8, by 5/8 = @ 1%, at full throttle @ 2%. A clip change from 2 to 3 = @ 1% more at idle, quickly climbs to 8% more at 1/8, then tapers gradually to less than 1% more at full throttle.