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#9 slide in PWK 250 carb anyone?


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Anyone tried the #9 slide in the YZ250 PWK carb?

I'm thinking of giving one a go. Seeking to further remove that 1/8th throttle rich burble.

Today I went up a size on my pilot. And for part throttle response at any RPMs with load, the bigger pilot is better. Same no spooge. But the rich burble at 1/8th throttle, low RPM and low load is back.

I have a mo-betta 295 with 1.3mm squish and 23.5cc head vol (head mods by Dave at TSP). Used with Aus 98 fuel (US 93 or 94) with 32:1 oil premix. At sea level. In temps between 15 and 40C (60 to 100F). Moderate humidity. Boyesen carbon Power Reeds. Gnarly pipe. Q-Stealth muffler.

Previously: Pilot=42, AS=1.3 out. Slide = #8. Needle = J. Clip = 3. Main = 170.

Today: Pilot=45, AS=2.0 out. Slide = #8. Needle = J. Clip = 3. Main = 170.

Want to try the #9 with those same jets and needle. In my motor, the #8 is certainly way better than the stock #7.

I know I should probably go get a Lecton shorty. But not yet ...

Edited by numroe
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I have the same engine and porting package as you and we both know jetting these things properly is a fine art. Mine has a slightly different carb being a RB modded 38.5mm bore, air striker, and a #8 slide. Pilot and main jets are easy to sort out but the slide and needles are the ones we tend to play with the least.

 

I'm dabbling with some different needles for this coming riding season to see if it helps achieve perfect jetting. I went with a slightly richer needle N3EH and plan on going to a lower pilot....I want to go slightly richer up the mid range because I believe the 1/8 burble that I also have can be cured with a lower pilot yet richer mid. If I race a long enduro and am on the pipe often I tend to get a slight lean surge in the mid range. I have a jetting graph that looks right if I go this route.I also have a stock RM250 N8RW needle to play with and see how that works out. 

 

I recommend ordering some extra clips because they tend to get slight bent when changing them out and could affect the needle height. You can also order needle shims if you really want to fine tune the needle heights....each shim = .5 clip height differential and it does make a difference in performance.      

Edited by primerib108
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primerib108, Needle clip shims are an interesting idea. I didn't know about those but am aware of the half-position needles.

The problem I want to fix does not feel controlled by needle height. Once I get to 1/4 open throttle and beyond the motor pulls hard and clean with the installed pilot, needle, main and pwr jet. I like to jet for torquey roll-on acceleration then have a main and pwr jet that pulls hardest at the upper revs.

Stock YZ250 owners might think why bother, and probably dont care much about 1/4 below throttle. But as you know the 295 at low to medium revs can bring on a lot of useable mumbo with just 1/8 throttle.

Idle can be OK with either pilot and correct air screw setting.

My jetting problem is at 1/8 to 1/4 throttle. I understand you suggest going leaner on the pilot then richer on the needle. That might work. But to totally remove the burble, I think a much leaner 40 pilot would be needed. But then I'd have to get a lot more fuel delivered around 1/4 throttle so a specific needle.

I found that with the richer 45 pilot, I get much (substantial!) better part throttle torque and response from idle all the way to 1/2 throttle. Interesting I still have no oil spooge. But the 1/8th burble comes back. Not as bad as with the #7 slide, but the burble is back and in some situations it means a delay or less precise power to the rear wheel. Not noticed in MX tracks, but certainly more annoying on trails or on roads connecting trails.

So it seems I have these options. All seem very feasible.

1. #9 slide. Since the #8 was so much better than the #7 for this problem area when slide just opens. My original question.

2. Rich (45) pilot and leaner (straight section) K needle. Seer's suggestion. Might work but I don't know exactly how the pilot and straight section "circuits" overlap.

3. Leaner (40 or 42) pilot and richer (straight section) H needle. primerib108's suggestion.

4. Different pilot and different (multi-taper) needle. rtv's suggestion. A possibly more accurate version of the previous options.

I like the thought of options 1 and 4.

Then there is the 5th option, and I know some will say just do it, is to get a Lectron shorty. But I'm hesitant to go that route when I could introduce many new problems, and local Aus support to tuning an Lectron for a 295 is an unknown. Plus my PWK solution seems so near and so cheap.

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I have a Mo Betta race gas 295 and I tried every needle combination and clip position including the Jd needles and still a rich burble. The solution believe it or not (for my motor at least) #8 slide and 40 power jet.

About a month ago, I tried that. Seeking to clean up this 1/8 burble. But I didn't like the smaller power jet. This was with the smaller 42 pilot. I found the stock #50 power jet works very well when open and needing torque at low to mid revs, then when it closes in the upper revs the power gain is substantial. see https://thumpertalk.com/topic/1115110-any-problems-if-i-put-non-tps-carby-on-to-a-tps-bike/#entry12072621
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Do the Kawasaki needles have a faster taper? My new to me CR needs more fuel at 1/2 to 3/4 throttle but not WOT.

I had a huge needle collection a few years ago but stupidly sold it when I bought a 4 stroke. Doh!

 

What year cr250? Are you using the stock  carb for that year or a newer PWK ? I would need to know what you have in the carb jetting  wise currently  to give you usable advise.

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Numroe, I'm not sure which J needle you are currently  using. I assume you are using either an N3CJ or an N3EJ needle, with N3EJ being 1/2 clip richer oem needle. There are also other slight variants of the Yamaha N3xx dual taper profile needle that I probably shouldn't get into here. If you want to use the Yamaha N3xx needles to clean up that 1/8 to 1/4 burble, your best bet would be to  use the leaner C version of the J needle first, and if that doesn't satisfy you, move to the N3EK needle with it's leaner starting diameter.

 

If you really want the bike to run clean down with great throttle response, I would recommend that you either use the Suzuki NExx triple taper needles or the Kawasaki/Suzuki N3xx triple taper needle. The NExx needles run very clean down low with great throttle response and a very linear type of power, which is nice for offrad use. For your bike I would recommend that you start off with an NECJ #3, 40 pilot and 170 main and AS@1.5. These needles also have a 1/2 clip brother, with the NEDx being 1/2 clip richer.

 

The Kawasaki/Suzuki N3xx needle are also very nice. I find them very similar to the NExx needles. The Kawasaki/ Suzuki N3xx needles are just as clean running down low and through the middle as the NExx needles ,but they seem to make the bike rev a little quicker. they are a fun needle to try. For your bike I would start out with and N3WK #3, 40 pilot and 170 main with the AS @ 1.5. The N3Yx is the 1/2 LEANer version of the needle.

 

Both of the above needles give up a touch of torque to the Yamaha N3xx needles, but more than make up for it in clean responsive type power.

I would try the above, before changing to the #9 slide.

If you do order the Kawasaki/Suzuki needle, order it through the  Suzuki part#(2000 rm250), It's much cheaper than Kawasaki part #. They are the exact same needle sold through both manufacturers.

Edited by rtv
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Numroe, I'm not sure which J needle you are currently  using. I assume you are using either an N3CJ or an N3EJ needle, with N3EJ being 1/2 clip richer oem needle. There are also other slight variants of the Yamaha N3xx dual taper profile needle that I probably shouldn't get into here. If you want to use the Yamaha N3xx needles to clean up that 1/8 to 1/4 burble, your best bet would be to  use the leaner C version of the J needle first, and if that doesn't satisfy you, move to the N3EK needle with it's leaner starting diameter.

 

If you really want the bike to run clean down with great throttle response, I would recommend that you either use the Suzuki NExx triple taper needles or the Kawasaki/Suzuki N3xx triple taper needle. The NExx needles run very clean down low with great throttle response and a very linear type of power, which is nice for offrad use. For your bike I would recommend that you start off with an NECJ #3, 40 pilot and 170 main and AS@1.5. These needles also have a 1/2 clip brother, with the NEDx being 1/2 clip richer.

 

The Kawasaki/Suzuki N3xx needle are also very nice. I find them very similar to the NExx needles. The Kawasaki/ Suzuki N3xx needles are just as clean running down low and through the middle as the NExx needles ,but they seem to make the bike rev a little quicker. they are a fun needle to try. For your bike I would start out with and N3WK #3, 40 pilot and 170 main with the AS @ 1.5. The N3Yx is the 1/2 LEANer version of the needle.

 

Both of the above needles give up a touch of torque to the Yamaha N3xx needles, but more than make up for it in clean responsive type power.

I would try the above, before changing to the #9 slide.

If you do order the Kawasaki/Suzuki needle, order it through the  Suzuki part#(2000 rm250), It's much cheaper than Kawasaki part #. They are the exact same needle sold through both manufacturers.

 

Just an FYI that these are not the keihin website codes but oem ones. Are you quoting the website codes maybe because I do not believe none the zook codes are N3xx?   

 

Suzuki RM250 - N8RF, N8RG, N8RG, N8RW

Kawasaki KX250 - N3WD, N3WE, N3WF, N3WG, NAFD, NAFE, NAFF, NAFG

 

I agree with your opinion thought that the triple tape would probably help with a nice rolling throttle response. Maybe the 1/4 throttle burble is a result from the N3E(x) single taper needles?

 

Numroe, The 45 pilot conundrum is aggravating the say the least, power is good down low but I find the spooge goes up too much for my liking. BTW, needle height plays a bigger factor than you think between 1/8 - 1/4 throttle. The x-factor being the pilot and slide as well....go too lean and you get some flat spots on the power curve. Same goes for too rich so finding the happy medium will take a bit of work without a doubt. But if that what it takes to get absolutely everything out of these 295's then so be it 🙂 Good luck though and post your results please because I am going down the same road as you.     

Edited by primerib108
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Just an FYI that these are not the keihin website codes but oem ones. Are you quoting the website codes maybe because I do not believe none the zook codes are N3xx?   

 

Suzuki RM250 - N8RF, N8RG, N8RG, N8RW

Kawasaki KX250 - N3WD, N3WE, N3WF, N3WG, NAFD, NAFE, NAFF, NAFG

 

I agree with your opinion thought that the triple tape would probably help with a nice rolling throttle response. Maybe the 1/4 throttle burble is a result from the N3E(x) single taper needles? The 45 pilot conundrum is aggravating the say the least, power is good but produces a lot of spooge.   

 

 

Yes, The needles that I listed are the motorcycle manufacturer's codes for the needles used in their bikes. The Keihin needles that I think you are talking about are single(straight) taper needles.

 

Lot's of the manufactures shared codes. The Yamaha N3C/Dxx dual taper needles were also used in KTM's and are actually slightly cheaper when bought through KTM. Suzuki and Kawasaki also shared the triple taper N3xx series needle in the late 90's-2000's http://www.partzilla.com/parts/detail/kawasaki/KP-16187-1079.html   http://www.partzilla.com/parts/detail/suzuki/SP-13383-37EQ0.html . Here is the part# for the Suzuki NECJ http://www.partzilla.com/parts/detail/suzuki/SP-13383-37FE0.html

 

I'm not sure if you know this or not, but that N8RW needle is only a little leaner on the starting diameter W vs H, than you N3EH, where as it is actually 1/2 clip position richer. on L-1. Those 2 dual taper needles (N3EH & N8RW) have the exact same taper profile with the only difference being the L-1 . N3Cx =clip position 1, N3Ex would = clip position 1.5 and the N8Rx is = 2. There is also an N2Zx which would = 2.5, and the newer N4D series that = 3.  They all use the exact same profile, with only the clip distance changing.

Edited by rtv
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Yes, The needles that I listed are the motorcycle manufacturer's codes for the needles used in their bikes. The Keihin needles that I think you are talking about are single(straight) taper needles.

 

Lot's of the manufactures shared codes. The Yamaha N3C/Dxx dual taper needles were also used in KTM's and are actually slightly cheaper when bought through KTM. Suzuki and Kawasaki also shared the triple taper N3xx series needle in the late 90's-2000's http://www.partzilla.com/parts/detail/kawasaki/KP-16187-1079.html   http://www.partzilla.com/parts/detail/suzuki/SP-13383-37EQ0.html . Here is the part# for the Suzuki NECJ http://www.partzilla.com/parts/detail/suzuki/SP-13383-37FE0.html

 

I'm not sure if you know this or not, but that N8RW needle is only a little leaner on the starting diameter W vs H, than you N3EH, where as it is actually 1/2 clip position richer. on L-1. Those 2 dual taper needles (N3EH & N8RW) have the exact same taper profile with the only difference being the L-1 . N3Cx =clip position 1, N3Ex would = clip position 1.5 and the N8Rx is = 2. There is also an N2Zx which would = 2.5, and the newer N4D series that = 3.  They all use the exact same profile, with only the clip distance changing.

 

Yup, that the zook needle I have is a tad leaner than the H. Between the stock yz250 N3EW and the N3EH + N8RW needles I bought I can really get into some fine tuning now + the 1/2 clip shims are going to be fun to play with too. My bike runs amazing 1/2 throttle and up......I am in the same boat as numroe trying to get the lower 1/2 throttle sorted out. I figure a tad fatter needle than stock will let me go lower in the pilot without lean surging. 

Edited by primerib108
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