PWK needle jets

headcoats · Post by **headcoats** » Sun Oct 18, 2009 10:30 am

In this pic are 3 jet needles from PWK 28's the tallest one is a KX 85 one but the other 2 are from KR carbs i have.
Question is what effect on fuelling do these have on the carb.
The internal diameters are all the same,only the heights are different

This pic has one of the KR jets fitted

KX 85 jet fitted

headcoats · Post by **headcoats** » Mon Oct 19, 2009 8:48 pm

Well...are you all running fuel injection

mj43 · Post by **mj43** » Mon Oct 19, 2009 8:52 pm

I guess it will affect fuel atomisation and low speed running.

Sorry can't be of any help never played with those - didn't even know they came out

TwoStroke Institute · Mon Oct 19, 2009 10:47 pm

Correct MJ. The shroud is there to extra low pressure area when signal strength from the engine is low. Typicaly low rpm/throttle

headcoats · Post by **headcoats** » Tue Oct 20, 2009 7:51 am

Hey Mr Two Stroke Centre could you explain it a bit more

Is the taller shroud like that then as it came from a KX 85 bike ? the pilot jet was #45 aswell.

So do the taller shroud and the bigger pilot jet be fitted together ?

the prob on my LC Hybrid is bogging pulling off ,even worse when cold and when it has warmed up,under light throttle openings it tend to stutter aboy 3000 revs.

kwackman12 · Post by **kwackman12** » Tue Oct 20, 2009 11:07 am

headcoats wrote:
the prob on my LC Hybrid is bogging pulling off ,even worse when cold and when it has warmed up,under light throttle openings it tend to stutter aboy 3000 revs.

This is the same problem I had with my my carbs, i'm still working on it but it is getting a better, at the moment my air screws are 1 & 3/4 turns out! Have a look at this posting viewtopic.php?t=5171 it explains it in terms even I can explain

headcoats · Post by **headcoats** » Tue Oct 20, 2009 3:23 pm

Interesting stuff
As mine are for a 350 YPVS engine mine were jetted with 150 mains and on the dyno the mixture was right apart from part throttle

As i'm running ramair pod filters then maybe the taller shrouded needle jet is the way to go ? but what i need to know is, does the taller shroud affect what size pilot jet you use and also does it affect airscrew position ?

KR-1R · Post by **KR-1R** » Tue Oct 20, 2009 8:23 pm

if you feel the air screw is helping fix your problem...

after youve run out of adjustment on that (all the way out) then its time to down size your pilot/slow jet.

next the straight diameter of the needle could be better at a different diameter (this part is the first to be exposed) when the throttle is pulled.

headcoats · Post by **headcoats** » Tue Oct 20, 2009 8:46 pm

I'm using the JJH needleson clip #5 highest/richest
150 main jets
42 pilots airscrew 1 1/2 turns out but also tried 1 1/4 out with no difference,also had it down to 1 turn out and 1 3/4 out.
ramair filters
Premix
it's nearly there but i think i will have a play with the tallest needle jet to see if it has any effect on part throttle.

TwoStroke Institute · Post by **TwoStroke Institute** » Tue Oct 20, 2009 9:26 pm

Try running the air box too, parallel twins with pod filters (K &N style seem to be worse) tend to have these sort of problems.

Airscrews (like just about anything else in carb) have a range they like to work in when you start to get to the extremities then time for a new needle, jet etc etc as abovementioned

The shroud itself won't be the cause of the stuttering

KR-1R · Post by **KR-1R** » Tue Oct 20, 2009 11:24 pm

the taller nozzle (~1.5mm to 2mm) will project into the slide cutaway. IF it fits, without jacking up the slide from allowing to close fully(careful) it will most likely have the same affect as a higher slide cutaway number - you might have a slide #6 (mm) installed but will behave like a 7.5 or 8. I think it will only affect the leaness off idle not where you are having the problem at 3000 (you must be on throttle by then).

...but being taller it may (*1) also move the point at which the fuelling is controlled from the diameter of the needle to the taper (might effectively lengthen the straight section of needle without affecting taper angle = SAME AS CLIP ADJUSTMENT if youre on CLIP 1 (TOP) and still need to go higher... points to your needle is at fault

(*1) It may be taller but are the insides lengthened as well?
From your first picture I cant agree that the internals are the same - left jet looks different from right one internally.

Clip 1 (TOP) = furthest from taper, lowers the needle into the jet, therefore makes it LEANER
Clip 5 (bottom) raises the needle out of the jet = more fuel, richer
youre at the end of adjustment - so the L1 or needle diameter or taper is incorrect (kind of linked together)

instead have you simply tried the KX needles instead of KR ones? four times less agrovation than pulling the carbs apart.

An airbox helps pull a CONSTANT moving stream of air into the motor (as well as tuned responses), without an airbox the carbs are grabbing at handfulls of still air or worse the carbs are fighting with an airstream working away from them.

NEEDLES ARE EASIEST TO CHANGE AND CAN BE DONE QUICKER
N427-68 (N68) NEEDLES COME IN 1.35 DEGREE ONLY (and single diameter) WITH 3 OPTIONS for L1 (only gives you about 1mm difference)
N427-46 series needles have lots of diameters, tapers and L1 options

THE SAME wrong NEEDLE CAN PRODUCE (SOLELY ON CLIP POSITION ALONE) A CROSS OVER POINT FROM BEING SLIGHTLY RICH AT 0-1/4 TO GOING SLIGHTLY LEAN UP TO 1/2 OPEN, then RICHENING GRADUALLY AGAIN UNTIL W.O.T. - compared with the ideal needle suited to your motor

headcoats · Post by **headcoats** » Wed Oct 21, 2009 8:31 am

That is a serious reply =D>
Thanks for the suggestions

The taller nozzle will fit the slide though as both carbs have a 3.5 cutaway

If i could get rid of the bogging,i could put up with the stuttering i think,the lesser of 2 evils.
I'll let you know what results i get

headcoats · Post by **headcoats** » Wed Oct 21, 2009 8:46 am

http://www.allensperformance.co.uk/data-n427-46.html

Click on the above link and it shows the figures for the jet needles

As the Kawasaki numbers don't translate,we were told to use "JJH" needles as comparisons.

Could someone look at the data and see if the JJH is the same as the latest KR1S needle

KR-1R · Post by **KR-1R** » Wed Oct 21, 2009 8:14 pm

for PWK28 needles 57mm long (PWK35 are 66mm long)

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headcoats · Post by **headcoats** » Wed Oct 21, 2009 8:22 pm

My brain has just exploded

soooo... are the JJH any good
It's just too much info for my monkey brain