keihin pwk slide mod?

[dg400sm]

i have a kdx220 with a pwk 36mm carb and rb mod already done. no matter how much try to jet this thing its always running rich at idle.(i live in the north of thailand where it is always hot and humid and i run the bike at about 3000ft)  it has a number 5 slide and the consensus seems to be a number 6 would lean it out.  given that slides are expensive has anybody ever modded a number 5 slide to match a number 6 or could anybody at least tell me how the slides are measured so i can work it out. cheers

[turbo dan]

You need to replace the jet block oring. 

[MatthewMCRepair]

6 hours ago, dg400sm said:

rich at idle.

Check what turbo dan said.

Throttle valve is most effective at 1/4 throttle position. A .5mm change is roughly a 5-10% change:

https://www.howtomotorcyclerepair.com/how-to-tune-throttle-valve-cutaway/

You might also want to see if the needle jet tube is worn. This circuit is not supposed to contribute to idle, however I have had instances where it definitely does if things are way out of whack.

 

 

Edited February 22, 2018 by MatthewMCRepair

[turbo dan]

https://www.ebay.com/itm/Jet-block-o-ring-1-Keihin-PWK-33-41-carburetor-35-36-38-39-40-mid-body-gasket-/201306545569

This oring fits all screw top PWK's and can be modified to work with the short body PWK38S as well if you're crafty.

[SS109]

I agree with Dan, I would replace the jet block gasket just to be sure. Seen lots of carb issues with PWK's that were solved by this little known gasket. If your carb has ever been soaked in carb cleaner it destroys this gasket and must be replaced.

4 hours ago, turbo dan said:

https://www.ebay.com/itm/Jet-block-o-ring-1-Keihin-PWK-33-41-carburetor-35-36-38-39-40-mid-body-gasket-/201306545569

This oring fits all screw top PWK's and can be modified to work with the short body PWK38S as well if you're crafty.

Just an FYI for those that have the short barreled PWK/PWM 38 carbs, my buddy Carlos Serrano (if you don't know who he is Google him and MX) has had the proper jet block gasket made for them. His shop is Serrano's Motorsports in Tucson, AZ (520) 294-9691. Tell him Kelly sent you!

[turbo dan]

My carb float bowl oring and jet block oring went flat simultaneously on my 05 KX.  Same material, no big surprise.

I've done a few of these things now and they have all looked horrible when you get the old one out.  Even if you think your bike is running fine, wait until you get a new jet block gasket in there.

[dg400sm]

11 hours ago, turbo dan said:

You need to replace the jet block oring. 

i replaced the jet block o ring last week,i should have mentioned that as i know its a common problem that will be mentioned. i've tried running the float height at 19mm all the way up to 23.5mm and to be honest it ran best at 23.5mm and that is with a number 35 pilot jet .ive also checked the fuel level using the clear tube method and at 20mm float height  the fuel level is level with the gasket mating service i will check if the needle jet tube is worn but i doubt it given that its a new carb although i dare say its a chinese knock off but with genuine keihin jets. i find the jd blue needle gives the best throttle response but the jd red neeedle is the only needle that will stop it running so rich at idle. i run the premix at 35:1. i have decarbonised the exhaust and muffler and made sure there is no leaks, the previous owner sold it because he couldn't get it running right and i am struggling to do the same,i also own a drz400 with a wideband sensor so i am no stranger to correct AFR's. i live in the north of thailand where the weather is 35 celsius,80 percent humidity and altitude about 3000ft. i might contact ron black at rb mods and see if i can give me any info on the slide,the way i understand it is the slide is effective from idle to 1/4 throttle. from all the things i have done the mixture screw can be wound all the way out and the bike still does not stall but it does still with less that 1.5 turns 

[turbo dan]

Chinese knock off carb?  Might be the whole problem right there.

Other than the carb though, it could be crank seals or damaged reeds as well causing your fueling issues.  I run the stock slide and stock needle up at 5500-6000 feet and it is crisper than you can imagine.  Not a hint of four stroking, zero pipe spooge.  When it is working correctly that PWK is an excellent carb.  I would worry that there may be something about the knock off that isn't quite right. 

[dg400sm]

9 hours ago, turbo dan said:

Chinese knock off carb?  Might be the whole problem right there.

Other than the carb though, it could be crank seals or damaged reeds as well causing your fueling issues.  I run the stock slide and stock needle up at 5500-6000 feet and it is crisper than you can imagine.  Not a hint of four stroking, zero pipe spooge.  When it is working correctly that PWK is an excellent carb.  I would worry that there may be something about the knock off that isn't quite right. 

you might be right,i measured the slide cutaway today and it is much bigger than a number 5 so the rb mod must have been done to the slide too,now i have no ideas,guess i either check for other sources to the problem or borrow/buy a new carb

[MatthewMCRepair]

 

10 hours ago, dg400sm said:

i dare say its a chinese knock 

I'd get a genuine keihin. You may have saved $ by buying chinese, however look at the time and money you are going to be putting in this chinese carb to get it to run properly. IF you ever get there.

You mentioned genuine jets are in the chinese carb, however all the air bleeds, passages, play a role in as well. Don't think for a sec that the QC of the chinese body is equivalent.   

[dg400sm]

Just now, MatthewMCRepair said:

 

I'd get a genuine keihin. You may have saved $ by buying chinese, however look at the time and money you are going to be putting in this chinese carb to get it to run properly. IF you ever get there.

You mentioned genuine jets are in the chinese carb, however all the air bleeds, passages, play a role in as well. Don't think for a sec that the QC of the chinese body is equivalent.   

it was on the bike when i bought it with the rb mod already done. i switched out the jets that were in it to genuine keihin jets just to make fault finding a little easier