Jetting

[pdxjim]

... is a pain in the ass.

Got my PWK28s setup on my LC with specs suggested by a friend down in SF with the same setup.

45 pilots, JJH needles @#2, 145 mains.

Lots of clutch slipping to get off the line, but idle isn't hanging, so i assume the pilots are close enough.

It runs better when cold and gets worse as it gets hot, so I can only assume the needles are lean and need to raise up a clip or two.

Would be nice to have a warm dry day, coz chipping away at this between rain showers is slow going.

Bacon 

[Barrie]

That says to me It's rich to start with when cold.
Start by getting the main jet near enough, if it idles ok the move to looking at the needle and jet assembly,

[pdxjim]

That says to me It's rich to start with when cold.
Start by getting the main jet near enough, if it idles ok the move to looking at the needle and jet assembly,

I've always done the reverse.

Get the idle/pilot and air/fuel screw dialed in.  Then move on to the needle.  Then the main.

All the jets are flowing when on the main, so no use worrying about it, until everything else is right.

I've also come to read "The general consensus is use JJH needles with the airbox and N68A needles with foam filters".

So, I'll stick the N68A's in and see if that helps. 

[Barrie]

OK. if you know WOT is about right, then decide whether your rich or lean in the middle, from your description it sounds rich when hot, so the needle needs to dropped a couple of notches . Your right about it being the sum of the pilot and the main , but if it idles with around 1 turn out on the air screw the mid range only is your problem which is only controlled on the needle up to 75% throttle, after that it's main jet to fine tune again

[SoCal250]

I've always done the reverse.

Get the idle/pilot and air/fuel screw dialed in.  Then move on to the needle.  Then the main.

This is the correct procedure 

[m in sc]

pilots big. I think its affecting needle. 42 pilot, 1 rich needle, 150 mains to start. 

[pdxjim]

I found a pair of 42's in my stash.

I'll put those in when the N68A needles show up.

[85RZwade]

I have a good stash of Keihin jets if you need something. KTM, you know.

[pdxjim]

I have a good stash of Keihin jets if you need something. KTM, you know.

Polini jets are cheap and readily available here in town, as the mopeders and scooter bois all run PWKs or clones.

I've not used them, or compared the Polini to genuine Kehin, but I expect they are good quality.

[pdxjim]

Scored a pair of 38's and a pair of 40's from the scooter bois for $10 total. 

Polini jets, but beggars ...

I dropped the 42's in anyway, coz lots of guys in the UK use 40's with the airbox so ... I gotta be bigger than that with pods, right?

Gonna change the needles out to N68A middle clip.

On second thought, it's not the jetting itself that's a hassle, it's taking everything apart right after I just put the damn thing all back together.  Over and over.

... and spilling gas all over my brand new build, and huffing gas fumes, and ....



I will say, I'm pretty impressed with this PJ1 Engine and Case paint I used.  It's holding up surprisingly well.

[Barrie]

Go to the local model shop and get some 2 part fuel proofer  , matt and gloss is available , over here we call it Aerocote
(UK).Spray a light coat over the finished paintwork, spilt fuel will then not affect the paint finish.

[pdxjim]

Ok.

Swapped in 42 pilots.  All else the same.

Still won't pull itself off the line and just basically bogs out and dies.  Won't idle.  Unrideable.

Totally rideable, and runs pretty good with chokes on, tho.

[rodneya]

Sounds like you are too lean.

Setting pilot, needle and then main works if you are already jetted close to perfect.
New build with new carbs, I would be starting out with getting the main jet close first.
Although the pilot does theoretically affect the entire throttle opening range, it is soo small that I just ignore it to start.

Everybody may not agree, just my 

[pdxjim]

Sounds like you are too lean.

Setting pilot, needle and then main works if you are already jetted close to perfect.
New build with new carbs, I would be starting out with getting the main jet close first.
Although the pilot does theoretically affect the entire throttle opening range, it is soo small that I just ignore it to start.

Everybody may not agree, just my 

That's the way it feels to me too.  It running better with the chokes on kinda confirms it.

It pulls great on the mains, it's just getting there that's bad.

I'll probably throw the 38's in just to be sure, then see if the scooter bois have any 50 pilots 

[85RZwade]

I only have four 50s. Less than two hours ride (brrr) or a couple days by mail. I'd send the shiny ones.