Keihin PWK #5 slide --> #7

[jayc]

I am convinced that my '02 125xc's chronic fart off the bottom is the result of a too-rich slide. It's Keihin PWK has a #5 slide. I want to make it into a #7 (with a little dremel work). Anyone have directions on what to take off?

Thanks - JayC

[GMP]

I think thats too lean. Why not try a #6 first, borrow one if possible before cutting yours. You can't go back once you cut.

[jayc]

Originally Posted by GMP

I think thats too lean. Why not try a #6 first, borrow one if possible before cutting yours. You can't go back once you cut.

Once I figure out how to calibrate the slide cutaway, I will surely take it off a bit at a time. I think ALL of the later model Gassers use #7 slides. I read a post by somebody that mentioned #6 is stock on the '02 125 (and that it is too rich). Why mine has a #5 in there is beyond me.

It's pretty rich through that range - idles clean and had good throttle response right off idle (45 pilot), but burbles and is weak at low throttle input (which where I am most of the time). It loads up after a while, then smokes like a 70's vintage DDT truck once I open it up until it clears out once on the high needle (unmarked LTR, I think) and main (162). The high-end is very close - throttle response is adequately snappy, and it screams like a raped ape and pulls hard at WFO.

Another friend suggested borrowing a slide too - as I told him, not only do I not know anyone with a spare slide, I don't even know anyone who owns a dirtbike any more!

Thanks - JayC

[MJC]

Jay, Changing the slide cut away is really easy to do. I've done it a bunch of times to different bikes. It effects the transition off the pilot and onto the needle. Which sounds like the area you are describing.

The difference between a #5 slide and a #6 is 1mm or .0040 of an inch.

here's what you'll need.

1- vernier caliper.
2- a black magic marker or dykem blue for marking the slide where you what to FILE it.
3- half round file. Like this http://www.amazon.com/Reciprotools-R..._bxgy_hi_img_c I don't recommend a Dremel tool unless your really good with it. They simply cut too fast for a lot people.
4- 300 grit sandpaper

Remove the slide. Locate the halfmoon shaped cut out,located on the air filter side of the slide. Take your marker and mark about this much [ ] above and around the entire outer most edge of the halfmoon. Next take your calipers and scribe a line, .5mm would equal a #5.5 slide or 1mm would= a # 6 in your case ,around the outermost edge of the halfmoon all the way around it. Now you will want to take your hand file and blend, keeping the same angle of the slide, up to the line that you just scribed. Take the sand paper and sand the edge of the slide you just filed until it's nice and smooth, you shouldn't be cutting with the sandpaper, just smoothing. Thats it. Now reinstall the slide back into the carb.

[jayc]

Originally Posted by MJC

Jay, Changing the slide cut away is really easy to do. I've done it a bunch of times to different bikes.

Thanks! I thought the measurement as you described was the case, but wasn't absolutely sure.

Now you will want to take your hand file and blend, keeping the same angle of the slide, up to the line that you just scribed.

Just so I'm clear, do you re-bevel the whole curved area under the slide so that the cutout is a straight line from the new cut to the front of the slide (increasing the angle of the cutaway), or curve the new cut into the existing area on the bottom. I'm thinking the former...

JayC

[MJC]

Originally Posted by jayc

Just so I'm clear, do you re-bevel the whole curved area under the slide so that the cutout is a straight line from the new cut to the front of the slide (increasing the angle of the cutaway), or curve the new cut into the existing area on the bottom. I'm thinking the former...

JayC

I'm not sure what you mean by Under the slide? Nothing under the slide is getting cut. The cutout should look exactly as it does now,the same tapper, but 1mm wider all the way around it. If it's done right no one will even know it been cut.

[jayc]

I'm referring to the taper that is on the bottom of the side, which I guess is the actual cutaway.

Like this:


First would be original, second is a re-taper (I'm assuming this is what I want), and third would be opening up the intake side, but preserving the taper under the slide. Clear as mud?

JayC

[MJC]

Originally Posted by jayc

I'm referring to the taper that is on the bottom of the side, which I guess is the actual cutaway.

Like this:


First would be original, second is a re-taper (I'm assuming this is what I want), and third would be opening up the intake side, but preserving the taper under the slide. Clear as mud?

JayC

It should look like the first drawing. Your not changing the taper. You're just making the opening of the cutaway a little bit larger all the way around.

[Jakobi]

I'm surprised no one else has mentioned it, but another work around is to alter the needle diameter to change the transition from the pilot onto the needle. You will need to retune your pilot circuit a bit to achieve this though and depending on how far out the slide cutaway is it may or may not solve your issues.

[GMP]

The '02 XC125 we had came wit a #5 slide. I worked out some jetting with DGH needle that worked well, thought I gave you the specs at one time. #6 maybe, but #7 seems quite lean for a 125. The 250s like the #7 with a much bigger signature.