Keihin PWK Questions

Zerotact

Subscriber
Joined
Dec 10, 2002
Messages
1,001
Likes
0
#1
HI,

   There have been some questions and debates over ??Pwk carbs  in the KDX section, and I was hoping to bring this question to more diverse set of ears than just the kdx crowd...   Basically,what is the diffrence between the regualr PWK and the Air striker PWK ?   What this boils down to is I can get  a 35mm air striker pwk for about the same as sending  my 33mm carb off to Rb designs for thier "mod"...

Any suggestions, advice?
 

Big Daddy

Subscriber
Joined
Dec 10, 2002
Messages
32
Likes
0
#2
Air strikers have two fins on the intake side at the bottom of the bell. This is to increase air speed up to 1/4 open.
 
Joined
Jun 3, 2003
Messages
74
Likes
0
#3
Zerotact, I noticed your from KC. Do you live in the actual city or a metro-branch from it. I live in Lee's Summit.
 

Zerotact

Subscriber
Joined
Dec 10, 2002
Messages
1,001
Likes
0
#5
so, am I wrong in thinking that performing the RB mod to an airstiker cab, may result in the milling off of these fins?
 

Canadian Dave

Super Power AssClown
Joined
Apr 28, 1999
Messages
1,202
Likes
0
#6
No the fins would not be cut out of the air striker in the event it was modified by RB Designs as Ron installs the divider plate on the exit side of the carb and the wings are on the intake side of the carb. The stock KDX carb is different than the standard PWKs some one like Carb Parts Warehouse sells. They are basically an Airstriker with out the wings. That is to say they use the body of a standard PWK with the air striker's jet block and throttle valve.

The RB Designs carb would certainly out perform the airstriker if you're looking for better off idle throttle response. Depending on what modifications have been performed to your bike and your desired outcome there are likely a number of modifications you'll want to perform before looking to mod the carb however.
 

Zerotact

Subscriber
Joined
Dec 10, 2002
Messages
1,001
Likes
0
#7
Thanks Cd for an actual difinitive answer in stead of the pissing contest we had been into before you stepped in, but, do you mean there are other mods that should come first, even on the 33mm 220 carb?
 

bclapham

Lifetime Sponsor
Joined
Nov 5, 2001
Messages
4,340
Likes
0
#8
dave, ive got both an airstriker and a stock pwk 38mm and i am sure the stacks are the same so i am a little confused.

just out of interest, where are you up to with your yz??? did you try the non powerjet carb??? i'm keeping my yz, but as yet, i dont see any need to start swapping carbs and such (ive done more fiddling there on the rm than i care to remember but thats a different strory)- i think if you go for the non PJ then expect to mess with different sldies
 

Canadian Dave

Super Power AssClown
Joined
Apr 28, 1999
Messages
1,202
Likes
0
#9
Zerotact what I mean to say it that there are a number of modifications I would make to the bike before I got too carried away with bigger ticket items like the RB carb mod. Don’t get me wrong it works very well but, for example, I’d replace the stock pipe with a rev pipe on your 220, tweak the suspension, which often times means stiffer fork springs, have Eric Gorr modify the head etc before the carb mod. What I’m suggesting is to do things in stages ensuring that each additional modification enhances the previous mods to ensure you get the biggest bang for you buck once you are all finished. If you find the cost of the modified carb to be out of you price range you might consider having your 33mm carb bored to 36mm to improve top end power delivery. Any competent motorcycle/sled machine shop will be able to help you with that. Expect to pay about $50-65 CND. If they need details on how to bore just ask though any experienced shop will know what to do.

bclapham that might well be the case with a large body PWK (over 35mm) I’d have to take a look at my 39mm PWK to know for sure. The jet block and throttle valve on standard off the shelf small body PWKs as well as those used on 1994 and older KDXs uses a flat bottomed slide and flat topped jet block where the A.S. and PWKs on 1995 and newer KDXs uses a jet block with two fang like dams cast into the top of the jet block so the top of the jet block makes up a round shape to match the bore of the carb rather than dropping down to a flat area like the standard PWK. The bottom of the side on the standard PWKs is flat with a cut out for the jet screen, plus the standard cut out to direct air over the jet screen at lower throttle setting. The A.S. slide is concave on the bottom to match the profile of the reshaped jet screen i.e. fangs but are otherwise the same. The Nozzle heights are slightly different on both as well. The standard PWK’s jet screen is 0.5mm lower, if memory serves me right, I’d have to check my log book to be sure of that measurement.

I have installed a 39mm PWK on the YZ and to date its working MUCH better for what I use the bike for than the power jet equipped PWM it came with. I’m sure that’s mostly due to the fact that I have much more experience jetting standard PWKs and have a mess of single taper needles, slides etc. to work with plus its easier to jet given I don’t have to deal with the effects of the power jet. My goal is to jet out as much of the hit as possible for the smoothest power delivery I can get while retaining crisp throttle response especially at the transition between low on mid throttle settings. I’m sure given an investment in additional slides, 2x taper needles and power jets for the PWM I could get similar results, perhaps better results, with it as well and I’ll very likely do that some time in the future but for now I’ll do a little more fine tuning on the PWK.

I wish the carb was more accessible on the YZ and the jets/needle easier to get at. I was spoiled with the KDX and could easily make a dozen different jetting/needle adjustments on a short ride as all you had to do was loosen the clamps on the front and back of the carb, unscrew the cap and rotate it. There is lots of clearance on the KDX, not so with the YZ :(
 
Joined
Apr 24, 2003
Messages
8
Likes
0
#10
My two problems with my 38 mm PWK seem to butt heads with each other.

At the first start of the day (using the choke), the motor races like it has a LEAN pilot circuit. If I turn the choke off too soon and give it some throttle, the bike gasps and dies.

Underway, there is a horrible (and annoying) 4-stroke burble at 1/8 throttle, like the pilot circuit is too RICH. Lots of spooge at day's end (Amsoil 2000, 50:1). At idle, turning the a/s out has no effect on RPMs.

I'm desperate. Dave, where would you begin?

THANKS.
 

marcusgunby

Lifetime Sponsor
Joined
Jan 9, 2000
Messages
6,450
Likes
2
#11
Sounds like your pilot is lean but the needle is 0.5 clips to rich.This shows up on quater throttle.
 

FNG

Member
Joined
May 2, 2008
Messages
97
Likes
0
#12
I am new to the dirtbike scene, but have owned a snowmobile with Keihen carbs for 8 years now. I have learned, among other things, that the air screw we are used to on the Miks acts more like a fuel screw on the Keihens. Turning it out actually richens the bottom end.

I just picked up a 95 YZ 250 and it was pig rich on the bottom, I dropped the stock needle 1 clip and turned the "air screw" in from 2 turns out to 1.5 and the bottom end is much better.

Also these carbs are sensitive to 1/8 turns on this screw so keep that in mind as well.
 
Joined
Feb 15, 2010
Messages
107
Likes
2
#13
First you need to change the slide to a 5.5 or 6.0 mm one .

The stock slide should be a 5.0 , which makes it too rich and gives you that annoying stutter and lack of crisp throttle.

It took me a whole summer of experimenting with jetting as thats what everyone talks about but that didn't fix it.

You can have your slide machined by RB for $15 vs. paying $60-70 for a new one. :cool: