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PWK28 Needle Charts

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Hi:

Here's the bike that I'm working on:

2004 RM85 with PWK28 carb, Eric Gorr ported head, FMF SST pipe, FMF Shorty, VForce3 reeds, and running VP U4.4.

Before the porting and switch from pump gas, it ran well, maybe a little on the rich side. We only ran it maybe 3-4 times like that, and the plug was a chocolate brown color.

Once the porting was done, we switched to the U4.4, and now it is fouling the plug after maybe 15 minutes of racing. It also has a bog occasionally in the 1/2 to 3/4 throttle range. The carb is running a 122 main and 48 pilot, which are the smallest ones that I have for it. The PE28 carb that was originally on it had way bigger jets.

Since I didn't have any smaller jets yesterday, I took the needle all the way to the #1 position and leaned out the air screw. It got a little better, but still not fixed.

I'll order some smaller main jets for it this week, and I'd like to get a leaner needle for it, as well. The stock NBKF needle (for the YZ85 that the carb came off of) is currently in the bike.

I'd like to find a chart of the needles in order from leaner to richer so I can get a couple, but I haven't been able to find one online. Also there seems to be a couple of alternate naming schemes floating around out there that look like "JJK", and then numerical ones, too. If anybody has a chart like that, I'd appreciate it.

Thanks,

Matt

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I would also appreciate a chart or something similar!

I need to order a new needle for my PWK 28 - Possibly a 'NAPF' Needle instead of the 'NBKF' which is currently fitted!

Thanks and ATB

James

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So I found this in another thread:

YOU move the clip up to lean it out. So if you want to lean it out from 2nd clip, go to the 1st clip to the top. DO this first, and see if that helps.

If youre mainly riding MX, this bike is near perfect for that stock. THe triple taper gives the bike a snap and a hit that even RC would be impressed. If you're going to trail ride you should replace the stock NBKF needle w/ a needle w/ a larger dia. like an NBKG,2ndclip . This leans out the bottom end and works better for offroading, where you're mainly riding in the 1/16 to 3/8 throttle opening. Also helps w/ spooge control too.

YOu can also get 1/2 clip position needles from Yamaha if you want to fine tune the 1/4 to 1/2 throttle, and even though moving the clip up/down using one needle almost gets you there, sometimes a 1/2 clip change makes all the differencee in the world. The 1/2 clip needle that's leaner than the stock NBKF-#2 is NBLF@ #1 cip. 1/2 clip richer than stock is NBLF @ #3. THe 1/2 clip in the NBKG #2 needle is the NBLG #1(lean) or NBLG #3(richer).

You can also use a Kx85/100 needle that's supposed to work pretty well for more bottom end. They use an NAPE needle #3clip and an NAPF #4.

ANd you can also replace the stock triple taper needle w/ a straight taper needle if you want to smooth out the upper band hit that the YZ85 is famouns for, but you would also need to go up two sizes larger on the main because these needles have a sharper taper angle. The SUDCO equivalent to the stock NBKF is the JJF clip#3. NBLF equivalent is the JJG #3. With these straight taper, you'd want to start w/ a 150 main to start w. I wound up w/ a 148 main The pilot size wound up being 50, which I thought was a bit large.

SO to reiterate, change out the needle's diameter for 1/16 to 1/4 throttle, move the clip up/down for 1/4 to 1/2 throttle. ANd go w/ a straight taper needle if you want to tone down the MX hit.

I'm still struggling with determining what needle is a step or two leaner than a NBKF in the #1 position, while still maintaining some adjustability on both sides (i.e. not in the #1 or #5 needle grooves).

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Thanks for that Matt!

That has certainly help me - just one question though :

Why do some Needles have a 4 letter code, while others have 3 letters codes?

Thanks and ATB

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Sudco has their own numbering (lettering, actually) scheme.

Today I got to look at a page from their real, paper catalog, and I found something very interesting:

If you look at this page, http://www.sudco.com/keihin_jn4.html#pwk28, there is something missing, which is the label for the vertical axis of the chart, which reads "1/4 to 3/4 throttle", with a leaner and richer. The leaner is at the top of the chart and richer is at the bottom.

With that info, the chart makes a lot more sense. So it looks like the needles that I need would be HKF and HFF, not the JJG and JJH like I initially thought.

Here is the correct page/chart

059.jpg

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