PWK 28mm carb baseline

[royalt67]

I:I
I bought a Keihin PWK 28 from a guy on ebay that was supposed to be for a Blaster, but instead was a standard jetted carb. With the stock #38 pilot jet and #135 main jet it would barely run and wouldn't idle at all. Finally a very cool guy at SUDCO told me that they jet this carb specifically for a Blaster with a #50 pilot and #160 main. Still have to try it and see how it goes.

Also of note, he said that for every 2000 increase in altitude they reduce the main jet one size, and for every 4000 they reduce the pilot jet one size. Very good to know since I live at 4000ft.

These are just ballpark recommendations. but damn it's good to start SOMEWHERE!

 

[MTN13]

i have the same carb, and it was recommended to me to run a 150 main and a 38 pilot, but i have had it running with this and it pulls good through the middle and top but does nothing down low, it almost feels like its flooding out at low rpms, but it idles good so i really don't know which direction to go.

 

[royalt67]

I'm probably going to try a #48 or #45 first for the pilot (slow) jet. All I'm positive of right now is that with a #38 @ 4000ft this carb not only won't idle but won't run at all below about 1/3 throttle and even then it's impossible to keep at a constant rpm. Mind you this engine runs fine with the stock carb, I'm just looking for a little more power and throttle response and a flat-slide pwk is supposed to be a good choice.

 

[yfz450bence]

wierd, i can run the 38 pilot on my 30mm oko, here at sea level, its a little lean, but you shouldnt have to go abouve a 45 pilot and 160main jet, specially at your elevation., its reall easy to tell when the pilot is rich, it sputters so bad and doesnt have clean rev off the bottom

 

[royalt67]

wierd, i can run the 38 pilot on my 30mm oko, here at sea level, its a little lean, but you shouldnt have to go abouve a 45 pilot and 160main jet, specially at your elevation., its reall easy to tell when the pilot is rich, it sputters so bad and doesnt have clean rev off the bottom

Yeah that is weird. I hope it's not defective cuz the numbnut I bought it from on ebay has no intention of taking it back.

 

[FLOTEK]

i have the same carb, and it was recommended to me to run a 150 main and a 38 pilot, but i have had it running with this and it pulls good through the middle and top but does nothing down low, it almost feels like its flooding out at low rpms, but it idles good so i really don't know which direction to go.

adjust the needle then

 

[royalt67]

I wish it was that simple. I tried the idle air screw (idle speed screw too) at various locations, all the way in, 1 1/2 out, 2 out, 3 out. It acts like there is absolutely no fuel in the lower range.

I took it apart and hosed out the idle circuit, perhaps it was plugged, but I didn't find anything specific. I will put it in tonight, see if it runs at all with the #38, and step up a bit after that just to see what happens. More to come.

 

[royalt67]

Jetting update. Everybody says start fat, so I did.

At this point I have a 50 slow jet and I've put back the 135 main for the moment. My big prob is it still won't idle. I have the idle air screw all the way in and it almost wants to idle but not quite. I also have the idle speed screw almost all the way in. I'm thinking about going up to a 55 or 58.

Has anyone else ever had to jet the pilot this fat? This quad is modified but not radical. I'm starting to wonder if the idle circuit is plugged, it's an awfully tiny hole where it comes out in the carb throat.

 

[royalt67]

Ok, my bad. Found the idle problem. It's been that stupid TORS all along. The throttle switch was still hooked up and everytime I would let the throttle come down to the idle position it would kill the ignition! Unplugging it, the quad wouldn't run at all. I had to jump it and then it ran great. (I'm so sick of stupid safety interlocks!)

Current jetting is a #50 pilot and #155 main. I need to jet some more now that the idle prob is solved. It's pretty good on the main, nice plug color and we were running flat out quite a bit. I would like to jet the pilot just a bit less to see if there is some power to be picked up off the line and in the low end, but for now my local parts guy is out of smaller jets.

In general, it RUNS LIKE A RAPED APE.

 

[yfz450bence]

Ok, my bad. Found the idle problem. It's been that stupid TORS all along. The throttle switch was still hooked up and everytime I would let the throttle come down to the idle position it would kill the ignition! Unplugging it, the quad wouldn't run at all. I had to jump it and then it ran great. (I'm so sick of stupid safety interlocks!)

Current jetting is a #50 pilot and #155 main. I need to jet some more now that the idle prob is solved. It's pretty good on the main, nice plug color and we were running flat out quite a bit. I would like to jet the pilot just a bit less to see if there is some power to be picked up off the line and in the low end, but for now my local parts guy is out of smaller jets.

In general, it RUNS LIKE A RAPED APE.

ya the tors will do that lol. 155 sounds good for the main, 50 pilot seems fat, especially at your elevation. start with a 45 or 42, with air screw 1.5 turns out. whats the needle clip at? very important setting, find out where your needle clip is at, start at the 3rd or 4th clip down from the top, and keep raising it till it stops sputtering.

 

[royalt67]

yeah, I agree. I have a 45; I'll try it as soon as I get it back up again. (currently torn apart for susp. work) The clip is in #3 right now.

What do you mean "stop sputtering"?

 

[royalt67]

Update: After quite a bit of probs with fouled plugs, I realized that my "K&N" filter was really just a cheap knockoff and plugged up down in the pleats to boot! (shoulda checked after my son "cleaned" it) After throwing away that restrictive P-O-S and replacing it with a UNI, it really wants to breathe now.

Running at 1000 ft of altitude for the next couple weeks. Main is now 162 (and it wants more) and the pilot is 38, but it's too lean (hunts a bit). I'm going to try the 48 or 50 for this altitude.

 

[dygz21]

so would you say the carb is worth the 150 bucks or whatever? I think that is one of the things i will be buying this winter when i get a pipe too.

 

[royalt67]

Honestly, yeah, it was worth it. Out of the box it ran better than the stock Mikuni 26mm, but the real bonus has been the plug on the bottom that allows main jet changes in about two minutes flat without carb removal (after a bit of practice, lol). The flat slide design is supposed to increase throttle response and I'd have to say that is true, but to be fair, Mikuni and others have similar designs. This is definitely a good carb to have until major engine mods come into play, porting, big bore, etc.

I paid $200 for the Keihin off of ebay and I'm not disappointed with the purchase, but I've seen virtually identical OKOs (Keihin copies under license) for $100 or so and everyone here seems to think they are just fine too. BTW I think I saw a PWK 28 in the Marketplace section today for $75. Good deal.