Pwk jetting help

[Up north rider]

  Hey all 
I’m a little lost as to which needles to go with  
Just wondering if you guys could give me a little help. It would be much appreciated. 

I recently built a 421 assassin lp. cfm airbox with unipods, vf4’s, +5* timing 
24cc domes, and t5’s, dual Pingle (real one) and 28 Pwk’s. 
The needles Im using say 
N68a on them which is different then what is commonly talked about on other threads I’ve looked at. The thing is I have to run them at the highest clip position just for the motor to run smooth. The midrange plug chop still looks rich, What needle for the Pwk’s would you say is a good place to start given my setup?

[JerzOutlaw350]

It all depends on where or who you bought your 28mm pwk’s from. The place where I bought my carbs from are an authorized Sudco dealer and both my carbs came with 46-JJH needles. Now my friends 28mm pwk’s came with the N68A and I don’t know who or where he bought them from. 

[Up north rider]

I bought my carbs on Facebook marketplace. The guy I bought them from threw in needles with the carbs. They’re motoritec needles off Amazon, and they’re all n68a, n68b, n68c etc. They go all the way to n68j. The thing is even when I measure them with Calipers, they are all so close to the exact same size that I don’t pick up any change whatsoever on the calipers. I know that’s probably not how you measure them anyway. Im just looking for any
subtle difference that might give a clue. To sum this up all I’m looking for is a needle that I can at least start in the middle clip position and go up and down from there. I think I might be barking up the wrong tree with these 

Edited June 8, 2023 by Up north rider

[JerzOutlaw350]

First off you have to find out if the carbs you have are genuine keihin carbs and not Chinese knockoffs. Second if you genuine keihin carbs you should only use genuine keihin jets both pilots, mains, needles and any other carb parts. You can get them from Jetsrus.com or PJmotorsports.com . Go to Sudco.com  and they explain how to identify if you have a fake or real keihin carb. They also have information and charts about how jets and needles work. I would say get a pair of 46-JJH needles and start with a clip in the middle. 

 

[Up north rider]

So I confirmed my carbs are genuine per sudco’s description. I’m glad you mentioned that. I was completely unaware of how close the fake carbs can look to the real ones. Anyway, So you’re saying I should run a jjh needle. Why not a cel, or a dgk or any of the other popular needles people use for banshees. I’m not questioning your advice. I’m just curious as why you went with those over x needle. Thanks again 

[locogato11283]

You likely won’t notice the difference between needles. I have run CEL, DGK, etc. I couldn’t ever tell a difference. Just run what they came with.

[Up north rider]

So I bought genuine jjh needles to replace the knock off amazon ones. I started on the middle clip position. I was bogging and had lots of blue smoke. I knew I was rich so I kept going up the positions one by one and now I’m at the top again just like before. It’s okay the way it is but you definitely have to brake though a rough patch in the rpm range. It screams on top but mid is not so good. Especially went it gets warmer outside. I’m wondering if my foam filters and air box are choking it out a bit, and I should just switch to k&n clamp on filters. I realize my cpi pipes are a drag pipe but I would think I could at least get this midrange at little smoother. What do you guys think?

[ClaudeMachining]

So I bought genuine jjh needles to replace the knock off amazon ones. I started on the middle clip position. I was bogging and had lots of blue smoke. I knew I was rich so I kept going up the positions one by one and now I’m at the top again just like before. It’s okay the way it is but you definitely have to brake though a rough patch in the rpm range. It screams on top but mid is not so good. Especially went it gets warmer outside. I’m wondering if my foam filters and air box are choking it out a bit, and I should just switch to k&n clamp on filters. I realize my cpi pipes are a drag pipe but I would think I could at least get this midrange at little smoother. What do you guys think?

Top and bottom is easy to adjust.

Middle is the hardest range to set.

Envoyé de mon SM-S908W en utilisant Tapatalk

[ride.race.live]

easiest way I found to tune needle is to play around in the 1/4 throttle area  and aim for a smooth transition  as you roll into the throttle  (not stab it) 

your not going to have that motor with CPI's come alive at low rpm putting around and stabbing the throttle its going to load up and hesitate  unless you feather the clutch to pick up rpms.

usually or atleast from what ive found if you can get a smooth transition in the low end  your uptop  from 3/4 to wot follow suit permitting your main is where it needs to be. 

[gusto]

Sounds like pilot jet needs to go down a size. 

[Up north rider]

On 7/4/2023 at 3:36 PM, gusto said:

Sounds like pilot jet needs to go down a size. 

I think you are right. I might have been chasing my tail with the needles. 
 

I’m trying to set my air screws correctly based what I can get out of the forums. so correct me if I’m doing anything wrong. 

I purchased a sync tool from fast. I synced my carbs at idle and about an 1/8 throttle. Now to adjust the air screw am I’m supposed to supposed turn it counterclockwise (leaner) until I notice the bike start to build rpms kind of like it would be if you forgot the gas off. Then turn it clockwise(richer) about a 1/4 turn from there? Would that be correct procedure? Anyway, when I lean out the air screws there is zero noticeable difference in idle speed. I’m also blipping the throttle as I’m adjusting so it would adapt. So far I’m 3 turns and nothing has changed. Should I try 52 pilot jets? 

 

 

 

[gusto]

If it’s not idling up or down your pilot jet is still too big OR you may have an air leak.

[Up north rider]

On 7/8/2023 at 9:30 PM, gusto said:

If it’s not idling up or down your pilot jet is still too big OR you may have an air leak.

Here’s where I’m at. I don’t have my new pilots in yet, but I decided to do a leak down test anyway and I had zero loss in psi. The gauge held solid for more than ten minutes. 
So that’s good, but I was adjusting the needles and mains last weekend and I had it running nice besides the hesitation near 1/4ish throttle. I took it out for a ride last night and it seems my progress is lost. It doesn’t run the same in the middle or wot. I don’t why I can’t jet this thing. Could this be an electrical problem? What would cause it run great one day and not the next? I’m not a carb expert but it can’t be this hard. Lol
 

Thank you for all the help this far!

[JerzOutlaw350]

  What size main jets and pilot/slow jets do you have in the carbs right now and where’s your air screw set at? When it comes to tuning your carbs try doing one thing at a time and write down your changes so you don’t get yourself confused. You also have to look at your altitude and outside air temperature because they play a huge factor in being able to tune your carb properly. Keep in mind when you have hot and humid air temperatures outside then it will cause it to run rich and when you have cool or cold dry air temperatures outside it will cause it to run lean. It took me forever to get my 28mm pwk keihin carbs tuned and now it runs like a well oiled machine. 

[Up north rider]

Well, I think I figured out my problem. When I’d get to wot the engine wouldn’t sound smooth and would spin up fast and wouldn’t have as much power as before. So I did a compression test. 124 and 117psi are roughly my readings I’m getting. My engine is a 421 assassin with 24cc pump gas domes. I think I leaned it out with my jetting. The lower psi cylinder also had a torn exhaust o-ring. So multiple factors could have contributed. I didn’t put an hour meter on after I built it but I’d guess it has 20ish hours on it. Live and learn I guess. After I tear down the motor and see what’s wrong is it possible to just order pistons and rings for these nikasil cylinders or do I need them plated again?