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]

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-...Attachment/dp/B001CNE3SO/ref=pd_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]

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]

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]

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.

 

[MJC]

The one thing that I did notice on all the 125cc and 85cc bikes I've done this to, is it has a tendency to less the hit from lowend to midrange somewhat. That could be a good thing or a bad thing depending on how you want your power.

 

[Neil E.]

Comparison of a #6.5 slide and a #8 slide. The change in profile is like the result you would get from angling a milling cutter more. Note that the curvature intersects the bottom of the slide at the same place. The upper area moves back due to the angle.

 

[jayc]

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.

I'm just about convinced that your 125 had an air leak or something. I remember you telling me that you settled on a 205 main for your '02. When I got my bike, it would barely run with the 188 that was in there - it would just barf and spew smoke, and did little better all the way down through 170. I finally got it to rev out with a 168, and ultimately dropped to a 162, and it absolutely rips at WFO, though a hair lean (165 would be just right).

JayC

 

[jayc]

Comparison of a #6.5 slide and a #8 slide. The change in profile is like the result you would get from angling a milling cutter more. Note that the curvature intersects the bottom of the slide at the same place. The upper area moves back due to the angle.

Thank you - that answers my questions completely.

As it turns out, I did get a slide-borrowing offer from somebody I haven't actually met yet. A neighbor of my camp that I "met" on another forum, who I plan to meet and ride with come Spring, has one.

thanks again all - JayC

 

[GMP]

No air leak. I rebuilt the motor myself top to bottom, and it ran that jetting before and after. That bike did very well in a few mountain enduros, so no big power issues. Main was a 190, not a 205. The bike did have carbon reeds though, perhaps that changed things a bit. That lean of a main in a 125 does seem strange for a 38mm carb, its even lean for a 250 at sea level. Look at what the Husky guys are running with PWK conversions. Maybe your carb is worn, just a thought.

Is that Kevin's (fury1) old bike? I recognize that custom coil guard. I think he tried the DGH jetting and while not perfect is was in the ballpark.

 

[jayc]

No air leak. I rebuilt the motor myself top to bottom, and it ran that jetting before and after. That bike did very well in a few mountain enduros, so no big power issues. Main was a 190, not a 205. The bike did have carbon reeds though, perhaps that changed things a bit. That lean of a main in a 125 does seem strange for a 38mm carb, its even lean for a 250 at sea level. Look at what the Husky guys are running with PWK conversions. Maybe your carb is worn, just a thought.

Is that Kevin's (fury1) old bike? I recognize that custom coil guard. I think he tried the DGH jetting and while not perfect is was in the ballpark.

What's DGH jetting? Is is Kevin's old bike, but went thorough someone else inbetween - don't know if the jetting in the bike was the same as Kevin used. Worn carb? Without question...everything is pretty worn on that pile . There was a LOT of questionable work done by the kid I bought it from... He told me that it ran really great, but lied - barely ran at all. Low compression, smoked like hell and wouldn't rev out at all, even after a rebuild. Once I finally went with my gut and dropped the main down into the 160s, wow - what a difference. It still has nothing on the bottom (not convinced the PV is working right, but maybe it is normal), but it is crazy fast on top.

JayC

 

[GMP]

By DGH I mean the Keihin needle I used. Once jetted right, ours had good low end for a 125. My nephew made that thing fly, it could grunt and had enough top to almost Hi point the B class at one race if a check wasn't screwed up bad. Before I rejetted it low end was non-existent and it ws a bitch to ride. I think you likely have a worn nozzle in the carb, so the bike wants abnormally lean jetting to run. Float pivot could also be worn. Bad reeds will also make a bike run rich down low. I'd get the carb and the rest of the motor sorted before chasing jetting around.

BTW, I have a spare cylinder, head, and PV for that bike. Bought it for a big bore project and my brother sold the bike from under me. $100 + shipping gets you a spare.