PWK30 tuning issue on Hawk 250 w/ big bore, cam, ported head, exhaust

[TrustMeImAnEnginee]

I recently finished building up and breaking in my hawk 250 with the following mods:



motocult true250 big bore kit (cylinder, piston, thin steel head gasket, shim for the rocker assy.)
motocult 292 cam (with their roller lifters)
motocult ported head
Powercore 2 exhaust (sold as JFG on amazon)

Some more info, I'm running some 55mm silicone couplers from the stock airbox with the stock filter, but with the top cut wide open. mainly because I don't like having an exposed filter just hanging out on the side of the bike in rain or mud, and it keeps the PCV under vacuum somewhat. I also have a +2 degree timing advance key which didn't make it in time for the build, so I still need to install it, or if I can find one, a +4 deg key.

After doing break in with the nibbi PE28 with jetting unchanged from before the build which ran alright, I decided to switch it up. I got a nibbi PWK28 and PWK30. The PWK28 ran alright, could have done some more tuning since it mainly seemed to be to lean at idle even with a 35 pilot jet. But I jumped up to the PWK30 once I test fitted it with the different manifold coupler just to try, and found out it fit.

The issue I'm having is the pilot jet size for the PWK30 only goes down to #30 and that's what I have in it, but it's still rich at idle. I have the idle air screw about 3-1/2 turns out to get it idling decent when warmed up but it still blows a puff of black smoke out the exhast or dies after sitting at idle longer than about 30 seconds. Like excess fuel pools in the intake or something. The weather outside is cool (~60 F) and I'm at about sea level, so I'll probably need a leaner jet for warmer weather or if I somehow ever see any elevation.

Most run pod filters of some kind or another on aftermarket carbs, I can try that to see if it's a symptom of running the stock filter in the airbox with couplers to adapt to the PWK30. I'd rather upgrade the filter in the airbox if possible than switch completely to a pod though. If the carb is defective, or just too large for the bike even with the engine mods, I still have the PWK28 to revert to. The stock air filter isn't clogged up, still fairly fresh since I did used to run a pod filter.

Pics below are the PWK28 but I swapped the coupler on the carb to fit the larger diameter inlet on the PWK30. Also had the straight manifold which pushes the PWK carb too far back blocking access to the idle air screw installed in the first pic. It worked for the PE carb but I had to change it out.

https://www.chinariders.net/picture.php?albumid=541&pictureid=2455

https://www.chinariders.net/picture.php?albumid=541&pictureid=2454

[Notjoemechanic]

I ran into this same issue with the pwk30 but different bike. I just couldn't get it jetted lean enough at idle. What I did was die grind 1mm off the rounded opening on the bottom of the slide where the needle sticks out. It un shrouds the needle jet. This reduces the vacuum on the needle jet and kees it from pulling fuel through it at idle. On name brand carbs you can buy slides with different sized openings to correct this. I think nibbi pwk comes with a 5.5 or something. I am a cheap skate so I scribed a 1mm line and cut it out bigger with a carbide bur bit. I'm now 1.5 turns out with 30 jet. I would do just a little at a time and test. Hope this helps.

[TrustMeImAnEnginee]

Really good to know about the slide shape, I'd heard they came in different types to tune but didn't know how.

I've still been busy since I initially posted.

Swapped the PWK30 for another PWK30, same issue. Setting on both were 120 main which is what the nibbi comes with, needle one notch down (richer) from how it comes (to the middle slot on the needle), and 30 pilot jet. Now I realize that going richer on the needle probably didn't help anything. Tried K&N filter in the airbox, pod filter, and no filter at all. Maybe saw slight improvement with no filter, but I can't run the bike that way and the other options didn't do anything.

I noticed that my modified nibbi 38 to 33 intake coupler boot for the PWK30 had some big spaces inside with large diameter where I had it angled on the carb and manifold for functioning the same as the original boot on the manifold that fit the PWK28. I trimmed the boot at an angle on the ends so it would fit decent against the manifold and carb, not worried about it sealing since I clamped it down TIGHT and shaved the ridge inside off. The coupler is a little longer than it needs to be anyway (plenty of gap between the carb or manifold and the big center ridge), so it wasn't really an issue to shorten it. I think gasoline might have been hiding in these spaces and contributing to the issue. The original boot that fit the PWK28 is a lot better in terns of the center ridge suiting the angle, and fitting close to the carb and manifold.

I refitted the PWK28, tried to cheat and swap the pilot jet with the carb installed (it's a pain to remove even with the soft silicone coupler on the filter side) and broke the float while removing the float bowl in the tight space between the carb, exhaust, and starter.

When I was done ordering a replacement float I went looking for pilot jets again, found a 25 pilot jet sold by dime city cycles and an ebay listing offering a 28, but it was out of stock. Bought two 25 jets since they seem rare, haven't arrived yet.

For now I'll have to find some good resources to fill out my understanding and wrap up the PWK28 tuning once the new float gets here, enjoy the bike for a while.

I've got a few things to do before tinkering with the PWK30 again:
-other manifolds or making my own coupler boot for the PWK30
-different slides or get spare(s) to modify
-needles
-look for a 28 jet in case the 25 is too lean

links:

manifold I'm running (sold as part of a kit for a PE30, fits nibbi PWK28 too):
https://www.amazon.com/Carburetot-Manifold-Connector-Performance-Enhancement/dp/B0CDVWX9NF

I shaved the casting lines off the metal manifold where the boot clamps on the outside, and ground out the inside to have less sharp lip on the boot side, and better match the head port on the other side.

adapter coupler boot for nibbi PWK30:
https://www.amazon.com/Motorcycle-Carburetor-Manifold-Interface-Motorcross/dp/B0CGD6CQ1G


25 pilot jet:
https://www.dimecitycycles.com/pilot-jet-keihin-n424-21-type.html

[TrustMeImAnEnginee]

I scribbled this out to clarify, basically I had the carb and metal manifold in at an angle and the large gaps on the side internally are my concern. Originally the straight nibbi 38m to 33mm boot is too long (big gap all around on both ends) so trimming to fit at an angle against the carb and manifold wasn't an issue.

32495

[slithica]

Dude, wtf are you doing?


I used a 45 for my idle jet and a 135 for my main jet.



I have the same engine in my magician.



Your engine isn't getting enough air. Why are you using the stock air box?!



Why even change the carb from one that works fine?



I'm using a VM26 (30mm) chinese clone carb. It's worked great from day one, when I bought it 5 years ago for $30.


You don't need to buy specially branded parts to get it to run well.



I bought my big bore kit off of alibaba along with the cam/rollers for $90.



Mine makes slightly over 20hp. You're spending the price of the motorcycle on parts to make it faster... you should have just gotten a faster bike in the first place.





With the modifications you've made for it to run that rich with a 30 jet your carb is either defective, or you are starving it for air.



Run it without a filter attached and see if it's still stupidly rich and if it is put your other carb back on it and tune it.


edit: I see you tried some of that. Yeah it's starved for air with that stock air filter. Also, just use a different carb if it's not working?

I used this:https://www.amazon.com/gp/product/B07DXRJTZY/ref=ppx_od_dt_b_asin_title_s06?ie=UTF8&psc=1


as my intake filter and still use that style. They're surprisingly good at allowing airflow in and just barely fit.



https://www.chinariders.net/showthread.php?p=310472


See dans posting where he used something similar. It might help you out.

[Notjoemechanic]

No need to put some down on how they build their bike. Or how they spend their money. Some people myself included like to tinker and it's half the hobby. This is an affordable platform. Why put 20k in a rusted out classic car if you can only sell it for 10k? Who cares if it is what you like? Oh and the pwk is a nice upgrade for cheap. It made a big difference for me. It's just a pain to dial in.

[slithica]

This


"Dude, wtf are you doing?"


Is targeted at the awful intake setup you had in your picture. Don't argue, it's terrible. You know it is.


You can spend your money however you want, I'm just pointing out it's frivolously.



Nothing wrong with tinkering, that's basically what this forum is for.



The rest of your comment makes no sense. But alright.


Hope you get it running well.

[TrustMeImAnEnginee]

Oh yeah, it's overkill to modify the airbox vs a pod filter, but with the top cover of the airbox opened up I didn't see a difference between it with a K&N filter and a pod filter directly on the carb, and maybe a slight difference with no filter at all.

I tried a nibbi PWK30, then another nibbi PWK30, and they ran the same.

With the VM26 of course your jetting will be different, and it's good that it's in the normal ranges of jet sizes. I made this thread because others have put on PWK30 carbs and not had an issue, and I'm still having problems when running a pod filter like them. It might be a difference between other generic PWK30 carbs and the nibbi version in some way other than jetting, like the slide, needle, or just something in the design.

Also, when I was looking for big bore kits they needed to be turned on a lathe bigger than what I have to be fitted in the hawk engine case. Motocult did that as well as decking the cylinder, providing the thin head gasket, and a shim for the rockers to compensate for the lower head without needing shorter pushrods. I got the other parts from them at the same time, but honestly I can't say they're good even without considering the price, since I had to drill out some holes on the head for the rocker assy bolts and the rockers kinda sucked. Had to get another pair sent to get two decent ones.

I wouldn't recommend motocult for anything now.

[TrustMeImAnEnginee]

Also, anyone here who's modding could have been better off with a used Japanese bike, I can't deny that. But it's fun to squeeze out some performance from a bike in a box most wouldn't even consider, and it's a generally known quantity of crappiness unlike a used bike which can have all kinds of issues.

I've learned a lot working on a relatively low stakes bike which is cool too.

[slithica]

The motocult true 250 kit is the same as the $80 Alibaba stuff I bought. It's probably from the same factory. They're just resellers. I am fairly certain my bike and yours have the same engine. Nah I got mine for like $1500 shipped and spent maybe $500 on mods. It runs beautifully and it's nice. My only regret is it didn't come with a balance shaft and the newer ones do. It certainly vibrates.



They're cheap, just keep your mods cheap too.