Jump to content

pwk 28mm carb tuning


Recommended Posts

15 hours ago, Confederate said:

Simple old hot rodders tip, Lean is fast until sh?@ starts to melt.

Hopefully it melts before winter so I can learn how to rebuild an engine 😂

Maybe the tiny farthole on this T-6 muffler is the cause?  The outlet on this is quite a bit smaller I think than my previous PC T-4 exhaust which ran perfectly with the stock carb 45/120, '03-'05 needle jetting...

Link to comment
Share on other sites

On 9/7/2021 at 11:45 AM, Chuck. said:

Because all of the jetting circuits overlap a lot getting everything balanced can be daunting.

Maybe the difference is because of the height the needle jet protrudes into the carb throat. There are 2 different heights and it does make a difference on jetting.  The other issue is slide cut away. Several posts in this forum on PWK 28 needle jets. 

Daunting to say the least which is why I appreciate everyone here that has done the trial and error so that I don't have to.  Actually I never would have the patience or know-how to do it.  

I'm using the needle jet that came in the OEM Cr85 carb which is shorter than  the KX100 needle jet.  I have no clue if it is the same as the SUDCO needle jet but I meant to order one to try.  I did look it up a few months back and the SUDCO needle jet part number is the same as Jet's R Us and appears to be just what comes in the carb when you buy a standard PWK carb (not one made for some particular bike).  Whether that is what Honda used for the Cr85 and is in my carb who knows lol  

Link to comment
Share on other sites

15 hours ago, Baja runner said:

My first carb was a used cr85 carb the stock needle jet . Was not the same as sudco . Bike would not run correct till Sudco needle jet. 

Good to know!  After I made that post yesterday I ordered the 018-560 needle jet and main jet holder from Jets R Us to compare them.  

Link to comment
Share on other sites

I got my parts today and can say that the OEM Keihin PWK needle jet IS different from the Cr85 needle jet.
 

 At a quick glance they look the same but the opening is slightly larger in the Cr85 needle jet.  I took a random needle and measured how far it stuck out of each needle jet when seated all the way.  11.37mm for the oem needle jet and only 11.20 for the Cr85 needle jet.  Its enough that you can tell the difference by eye when looking through them both side by side (hard to see in pics).  

The main jet holders look identical but Ill be using the oem keihin parts from now on to be safe.  This should cure my overly rich condition!  Thanks Btr, I only wish I had just swapped parts to begin with but it is always a journey😂2577F464-A7FD-419A-ADDF-A1807584A4D7.thumb.jpeg.acee3b60ecfc1c9c9878cda6d64023d7.jpegB9CD260E-EAA6-4A25-A4E1-CBB49E5C2912.thumb.jpeg.b0faa15eee6da5c9a572b366fb6a056f.jpeg2EFA7581-B8FB-437F-8E1F-03A9BA7F9B86.thumb.jpeg.830f9713d4c68517fa2d05f412ad5bc9.jpeg815B2CDB-1B1E-40E3-9763-6471E5811425.thumb.jpeg.73f081e22081512dae3caf529a1ffab9.jpeg

  • Like 1
Link to comment
Share on other sites

Not to confuse the issue but rather to show that OEM use a variety of needle jets to fine tune for their engines. Here is a list of dimension for some needle jets that I have on hand. So when some one posts up jetting you need to know the needle jet, needle and clip, float level, and slide.

These need;e jets are all the same family and inter change. The higher the top protrudes into the venturi the greater the delay from slide cutaway to needle circuit, in effect delays the transition to the needle.  Seat is the distance from the surface that the NJ fits against in the carb body to the the top of the NJ. The last column is the location of the NJ orifice from the seat. This can be compensated via needle clip position.

Needle Jets………………………… LOA    Tower f/ seat        Orifice f/ seat
in XR carb (black mark) ….… 6.58 ……… 0.73 ………………. 5.85
Brass ………………………………… 6.61 ……… 1.29 …………………. 5.32
Silver ………………………………… 6.14 ……… 2.26 …………………. 3.88
Shorty ………………………………. 4.06 ……… 1.18 …………………. 2.88
PWK silver …………………..…… 3.97 ……… 1.30 …………………. 2.67
PWK Brass (in box) …………… 4.07 ……… 0.47 …………………. 3.60
PWK silver f/PWK …....……… 4.08 ……… 1.50 …………………. 2.58

Two NJ aligned on their seats

538675827_PWKNeddleJets(1).thumb.jpg.e1c055712947843b17ee820c948486b4.jpg

 

 

  • Helpful 2
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...