Another PWK28 jetting thread

[Luni]

So, Im trying to get my jetting on with my PWK 28 on my KOR ported engine, and its being a little hooker.

I seem to have got my pilot circuit jetted properly, Im sitting at a 40, with my needle in the middle on a NAPE needle. On my main, its kinda pissing me off. The bike pulls decent, then it kinda breaks up in the top side of the revs. Doesnt seem like it wants to respond to upping the main jet. Im running a 140 right now, but Ive tried going up and it doesnt seem to matter.

I had an issue where it didnt matter at all, what main I ran, I was up to a 160 and it still wasnt right, but when Id read the plug it was reading lean. I set my float level and that helped, I just wonder if maybe I need to check it again.

I dunno. Pilot circuit works pretty well. It might be a little fat on the pilot, but Im ok with that because when you roll off the throttle to start slowing down, the pilot is what is flowing fuel and if its fat, its cooling the piston off better.

The main is pissing me off. Ive cleaned the carb, all the passages, the jets, etc.

I wish I could get a wideband O2 sensor setup to work on there, or even a cheap EGT solution so I could see what my EGTs were doing.

I ordered a few other needles to try JJH and JJF I think, theyre both a little leaner in the mid than the NAPE but shouldnt affect the main at full WOT.

Blaner, I know youre running a PWK28. What jetting numbers did you end up with?

 

[98blaster+4]

ive got a pwk28 also. 50 pilot 158 main. when it runs its strong. i had a problem with it breaking up on the top too. kept giving her the main jet till 170. then as it got warmer i started coming back down.
have you done a leak test? could be why you are lean at wot.

 

[roadkill]

So, Im trying to get my jetting on with my PWK 28 on my KOR ported engine, and its being a little hooker.

I seem to have got my pilot circuit jetted properly, Im sitting at a 40, with my needle in the middle on a NAPE needle. On my main, its kinda pissing me off. The bike pulls decent, then it kinda breaks up in the top side of the revs. Doesnt seem like it wants to respond to upping the main jet. Im running a 140 right now, but Ive tried going up and it doesnt seem to matter.

I had an issue where it didnt matter at all, what main I ran, I was up to a 160 and it still wasnt right, but when Id read the plug it was reading lean. I set my float level and that helped, I just wonder if maybe I need to check it again.

I dunno. Pilot circuit works pretty well. It might be a little fat on the pilot, but Im ok with that because when you roll off the throttle to start slowing down, the pilot is what is flowing fuel and if its fat, its cooling the piston off better.

The main is pissing me off. Ive cleaned the carb, all the passages, the jets, etc.

I wish I could get a wideband O2 sensor setup to work on there, or even a cheap EGT solution so I could see what my EGTs were doing.

I ordered a few other needles to try JJH and JJF I think, theyre both a little leaner in the mid than the NAPE but shouldnt affect the main at full WOT.

Blaner, I know youre running a PWK28. What jetting numbers did you end up with?

i cant see you being rich with only a 40 pilot, on my engine with less mods, and an oko 28mm im running a 42 pilot and its a little bit lean

 

[Luni]

Its definately rich with a 40 pilot, if I go with a 45 its WAY too rich. On the 40 it still breaks up a little bit until I give it more throttle. The transition between pilot to needle is definately rich. Even at half throttle its somewhat rich. Just at WOT is where I cant seem to get no lovin. Its odd.

Im also at altitude here. Higher than most on this site. Im at ~4500 feet. That is alot different than the close to sea level altitudes most of you guys seem to be at.

Im gonna try going higher on mains, to see.

Putting it into perspective, before I blew my top end, I was at a 130 main and a 32 pilot I think. I ran it for 1 full season, never had issues till I developed an airleak and blew it up.

I ordered some different needles for it tho. I think when I put my JJH needle in, Im gonna run more pilot cause the JJH leans it out.

The needle im running is a very rich needle. Ive read when you have a really sharp tapered tip, you need less pilot because its actually taking gas through the main jet when it shouldnt be. It can also cause issues like Im having, so hopefully the needle(s) will help solve it for me.

I havent done a leakdown test yet, so I dont know its NOT running lean cause of an airleak, I guess Im just assuming that it isnt cause I replaced all the seals when I put everything back together.

 

[Zwiser]

id ask ken about the jetting since he ported it for you.

id say since he knows how he did the flow thru the ports hed probably know what the flow should be thru the jets.

 

[Luni]

Ken dont know nothing bout no PWK 28 carbs, only works with Mikunis. Im on my own.

Ill figure it out. Half of the reason why this thread is here is because Im having a problem, and as I work through it, Ill post, so others can use my trauma to help them.

 

[Blaner]

heu Luni, im still scratching my head, got a 48 pilot but only runs properly all the way in, iuts too lean and idles too fast at any turn out, need to get a 50 or 52 pilot, iv found mine is happy with a 152 main, but its my needle that is the problem, wanting to get a NAPF (kawasaki) or a NBKF (yamaha) which is the same as the JJH, still figuring all this needle rubbish out..very confusing

 

[Luni]

Im having a hard time with this whole thing.

From everything Im reading right now (Im spending hours pouring over PWK and carb related crap), your needle has nothing to do with WOT. So, I dont know what to do about that part.

I ordered the JJH needle, hopefully I get it soon. One thing Ive been reading is fuel level is critical, if its too low it will mimic a lean condition (which you can offset by running bigger pilots), and if its too high, it will mimic a rich condition (which you have to offset by running smaller jets)

Also, Ive noticed its very hard to actually properly check the float level cause the way youre measuring isnt necessarily precise. I dont have one of those float level gauges, and all I have is a ruler. So, I cant even really tell how accurate my float level job is. For all I know its too low, and thats why no matter what I do to the mains, its too lean. However it feels rich.

And maybe Im having an electrical issue and thats why its breaking up in the upper revs. I just dont know. I do know this. My quad does NOT feel as quick as it should be. It has a good healthy hit initially but it just doesnt hold it. There is no "on the pipe" feel at all. There isnt a "powerband" really. It just goes.

I kinda wish I had a stock carb to put on there and run some recommended jets on it. Cause tons of people on here run stock carbs, and theres tons of info on here about those.

Another thing Im gonna be doing as soon as my buddy gets off his ass and installs his bigger carb, is Im gonna be trying a PJ 34mm carb. If it works for me, it will be free.

And one final thing Im gonna do is go through and clean the fack out of this one again, Ive read the vent holes can get clogged up and simulate a lean condition (like Im having), and no matter what you do, it just wont flow enough fuel.

So tomorrow, Im gonna clean the fack out of it again, pulling off all my lines, cleaning THEM out, make sure theres no restrictions, make sure my petcock is flowing an adequate supply of fuel to keep the bowl full, and then run it with what I have.

I also have a dial a jet on there, but it doesnt seem to help much either. I think it adds some fuel, but if Im having a fueling issue in the first place, you know, from the carb itself, the dial a jet isnt gonna help if its running out of fuel too.

 

[Blaner]

they do seem to be alot of trouble these PWK's and OKO's, mine kicks like a hyper cat on main but is COMPLETELY dead between pilot and main, pulls off, dies, then you better hang on cause push through to WOT and it hits like a switch,

I put in the stock banshee needle and it has helped and the bog is much smaller, but i think its too rich as the OKO needle is a twin taper.

as for you, try a slightly richer jet, try extremes and see what happens, go to a 155 or so and see if anything changes.

i was hoping to get mine right by saturday but its not going to happen, i have a enduro and think il just swap back the trusty ol' 26 mikuni.

sigh......blastard keiheins....

 

[Luni]

I wish I had one of those colormatic 5000 things. Id put my ass end up on stands, and Id add a little parking brake to simulate some load, and Id put the bastard through the revs to see whats what.

 

[Blaner]

i must still put some pics up of it, its old school! but very clever, only problem is im not sure of the heat range of the glass plug it uses....which could be all the difference...

 

[Surfrjag]

it sux you 2 are having so much trouble with this carb i have used pwk and oko carbs with no troubles besides 1 time when i had the incorect specs on float level. i will say if you have a dial a jet on the carb if your float is too high it wont drain like a normal carb will because i think the dial a jet uses the overflow tube for fuel. find a micrometer and get an accurate reading. you dont need one of those specail tools either. good luck fellas

 

[Blaner]

so what is the correct float height and how exactly do you measure it with a steel ruler and a digital caliper?

 

[Luni]

On a PWK the dial a jet doesnt use the overflow, you drill and tap a hole into the bottom of the main jet cover bolt thingy ma bob.

So, my dial a jet pulls fuel from the very bottom of the carb. But in theory, shouldnt the dial a jet be good for a couple main sizes up and down?

 

[Luni]

so what is the correct float height and how exactly do you measure it with a steel ruler and a digital caliper?

Correct float height is 19mm. However, method of measurement is going to vary based on who you ask. Some say to just turn it upside down and measure from the bottom of the floats to the gasket sealing surface. The needle jet stops when the float is snugly touching it. This method makes the most sense to me. Some say to turn it on its side and measure from where it starts to open up, but that doesnt make sense to me cause youre measuring it CLOSED not starting to open.

I dunno. Thats another thing Im having a hell of a time getting. Honestly if this were a car forum, there would be writeups on all this stuff complete with pictures and videos, but I havent found a single comprehensive thing on this site on how to set float levels. And on Youtube, most of the videos are idiotic, or shot like crap, so theyre hard to see and understand.

I dunno. Im gonna play with it tomorrow. Ill let you guys know what I find. I really want this carb to work for me. I just dont know if its going to.

 

[Blaner]

mmm you are right, little info on such a topic, well rep awaits a detailed report on it. il have to play with mine some more too, althoug i dont think thats my problem.

by the way, i measure the bowl volume of the 26mikuni and the 30mmOKO and they are identical. i was worried though that the flow to the jets is impeded by the small gap the jet housing alloy casting leaves, and in the drain plug there are 2 holes that should allow fuel into the chamber from which the jets suck but when tightened, they do not line up with the cutouts allowing fuel to the holes! i grinded mine open a bit with a dremel..pics coming...this may effect fuel supply ti the jets!

 

[98blaster+4]

mine was finiky for me to, i have mine jetted for 1500-4200 ft so i feel ya on the elevation.
you really gotta get a leak test done. new seals or not. you will not get good jetting results if your leaking.

 

[Blaner]

mine is sealed, i think i have isolated my issue to needing a leaner needle.

 

[98blaster+4]

i know about the holes you are talking. in the plug that threads into the bowl,right?
they dont seem to be a concern for fuel flow. i tightened mine enough so that the holes line up with the grooves, but no difference.
sicivicdude knows about the needles pretty good, he helped me out.
in my thread about "random dying out" in the engine section i have posted a bunch of pictures of the inside of the bowl on a pwk28

 

[Surfrjag]

Ok I never used the dial a jet so I don't really know about those. As for setting float height, you will turn it on its side and when the needle valve is closed but spring is not compressed is when you measure from the bottom of the carb body where the bowl screws on to the furthes point on the floats is where you want to measure. Hope this helps..