Modern Vespa

Hey guys... So next project is calling for a bigger carb than my usual 30mm PHBH, I'm looking to use a Keihin PWK 38mm Air Sticker. So obviously all the needles, jets, etc are different numbering system to the PHBH, so my query is, is there anything available (or that you could share) that shows such things as numbering, lean to rich in needles and jets? TIA


Keihin PWK 38mm Air Sticker

Next project... nearing completion

Chandler shared this with me.

Setting up the carb was pretty easy, but I've also gotten all the cheater tools working. I'm running a PWK-34, so I can use https://kyajet.de/ to model jetting changes, plus CHT, EGT, and Air-Fuel Meter

The needle chart was pretty useful for the pwk 35 I had…

Geez, I knew they were a little harder to get your head around than the PHBH but, ha!! I guess I'm just so used to the PHBH. Thanks guys, that table looks pretty helpful 108.

Ah, it's not too bad, it's a similar thing.

Just the PHBH is easier (and cheaper) to control the variables…

The PWK slides cost way too much.

Not sure if it is the case for you, but I found the most important thing (if you don't have a dyno) is to be able to tell the difference between too lean conditions and too rich.

That's probably why folks end up going in circles, myself included.

Feels and sounds very very similar, but how the engine reacts before and after throttle positions seems key.

Your engine seems to deserve it, will be awesome to see how it runs!

Mine is a 35 AirStriker (on 221 MHR reed induction), and the first thing I did was buy a no. 6 slide to replace the no. 4.5 that comes in the carb. For me that was a necessary starting point, and then it was down to needles and jets for fine tuning. Not sure if this applies to the 38. Several (mainly GSF) references suggested & supported the slide change.

Oh, okay. So what's the scale for the slides? PHBH has 30 being the richest up to I think 60 being the leanest.... Does the 38 Air Striker have similar?

Personally, I would try to set up the slide that you have first. The 38 is not the 35 after all and buying slides gets expensive.
The slide and the needle diameter work the same area. If the slide is too rich, a larger diameter and richer taper compensate. And ends up pretty much the same.

Hey Jack, I haven't got any PWK stuff... just got the 30mm PHBH at the moment. Still deciding which way to go with it.

Slides for the pwk are similar… smaller number is richer.

On GSF, most people seem to be using 6,6.5

The 35 AS comes with a 4.5, but I also ended up with a 6 slide…

Similar for the AirStrikers (the non-AS PWKs use different slides). The bigger the number, the leaner the slide. The OOTB 4.5 is very rich, and I couldn't find needles that would compensate enough, hence why, for me, the 6 became the starting point. Maybe there is something in between that would work for you, and as Jack suggests, you _may_ get there with a 4.5, but I somewhat doubt it. Assuming you do need to go leaner, you can work on the existing slide with a Dremel to take the arch up bit by bit until you're satisfied. This way you would avoid the cost of a new slide (60 GBP in the UK during 2018), and you would be able to fine tune the slide arch height. For example, you may find that 4.9 or 5.3 is the best for you, but in between any slide that you could buy.

Thanks for all your inputs guys, just keep in mind, I haven't even got one yet!! As I mentioned, just wanting some info on jet/needles/slides, what's lean, what's rich. I remember researching PHBH info and coming across tables from MB Developments I think, and it had a lot of good info on there... I'll post it up if I can find it, might be helpful to someone.

I know of which one, great info.

Mark is a gent, brought a bunch of phbh parts from him.




These tables right?

Yeah!! That's the one.. was really helpful for the PHBH, It's great that they mark the most commonly used bits, couldn't find anything like that for the keihin 38mm. I guess it'll just be a matter of biting the bullet and then trying to work it out once it's on. I wanted to order bits from SIP that I might need while I was ordering anyway.

Just properly checked out the https://kyajet.de/, it's a pretty cool tool to use, helps you get a visual of what your changing.

What you building that might need such a large carb?
Best carb of such size is a VHSC39, they are expensive though.

BFA306.. I've currently just got a PHBH on it, as per the pic. I've built it as a plug n play motor, I should give it what it deserves hence why I'm trying to decide on a bigger carb. Not after a big hp powerhouse as it's more than enough as a plug n play engine. It'll be used as a commuter, tourer and everything in between.

Stuart Declan from SA has until recently run a 38 PWK on his 221 MHR. Seemed to have it dialed in pretty well, he'd be happy to let you in to his jetting.

Interested too! Post the finding here

Given your specs (BFA), not yet purchased, and goals (ultimate tour/power everywhere) wonder if you've considered the smart carb.
Im using the 28mm (punny compared to yours...) but am a fan.
Positives - feels like fuel injection - smooth
Great power
Surprising fuel economy (good)

Perhaps those are just the marks of a well tuned carb.
After all - its just fuel and air at the end of the day.
SC markets their fine mist like atomization - and I think there is something to it based on my experience - but endless tweaking with traditional carbs could perhaps come close.

Hey charlieman22, so tell me more about your setup? So, I've got a 28mm SC on the shelf which I bought for my 252 quattrini, it always ran rich at idle 1/8 throttle, no matter what I did I couldn't get it to run leaner down low so I basically shelved it. I'm interested to hear about yours.... I did try it on the 306 and it was same down low, once it got half to 3/4 throttle it was really smooth and had all the traits that you've mentioned. I will end up getting a 35mm PWK for the 306 but will contact Nathan from SC to try and sort out what the issue is with the SC.

Stuart - are you running EQ rods?
Something like a 28?
I was an early adopter - and worked with the owner.
He was using a different taper rod for the parasail world - and I experimented with those.
EK series.
They were instantly fantastic.

I would guess you will be somewhere up around 105-110 clicks on an EK rod.
Probably a 28, but perhaps a 27.
I found my tuned motor ran great on 27 - but screamed on the 28...

Lemme know which series of needle you were running.
SC does a 35mm I think.

Yes, been running the E-Q series needles? So are you saying that they're not right? So the E-K fixed the rich symptoms? I bought everything from E-Q26 - E-Q30, all had the same symptoms down low which I now know that they do as that's how they work, lower number just means richer mid/high range... basically. I got my Malossi air bellows to fit the SC intake so, for me, it'd be cool to use!!

Stuart -
Yup.
Those EQ's are the issue.
The EK's will work really nicely for you.
Pro Tip - SC will let you swap them out in all likelihood - so you might be able to get a set of EK's in exchange for your EQ's.

The EK's have a steeper taper.
Should set up around 105 to 115 clicks.
Here are a couple hacks I like to use.

1. when you put the new rods in - screw the barrel on exactly two turns. This is 8 clicks per turn worth. That will speed set up (don't have to click 100 times) and you can just start leaning it.
2. You know you are too lean when you blip the throttle (with its awesome new response) and it doesn't fall back quickly to idle.

Done

Edit: I am running about 200CC, long stroke crank, pipe, 181 ex. timing. Use the EK28.
Will run pretty damn good on the 27 as noted - but still a little rich in lower throttle and not as much zip at the top either.
If you are near my specs with port timing - expect you to be around that EK28 as well.

Nice man.. that's worth a try... are you running a pump too?

Great.
Suspect you're gonna love the EK's.
Couple things I should mention:

- I kept it rotary - but its somewhat... unique. I fabricated a new rotary pad for the cases that is L shaped. Makes it extra wide. Seals on side rather than face of crank web. So even if you are running reeds - my data should still be in the ball park.
- No pump. Carb sits low on motor. Built a custom intake. Some pics below. Discovered I could run the SC at 40° angle without trouble. the 28mm has such a deep float chamber.
- I ran it in a rally about a month ago. we did about 100 miles. I was worried about making the petrol station half way. Had been running it hard. turned out to use only about a gallon on 50 miles. I was impressed.
- You can hear it run here if you want: (dyno tested and swapped from EK27 to EK28 in this vid).


Rotary pad has an L shaped hole.

this blue edge on side of crank is what my rotary seals on

intake manifold as I was fabricating

Carb mounted - you can see the angle pretty well here.

Nicely tucked in means it fits under my VBB cowls. sits at 40°. Low enough that I don't need a pump. Keeps it simple.

Sounds great, nice n crisp.... I've got a pending SIP order a the moment so emailed to see if they can throw a 28 in the order.

looks like you have some pretty spectacular hardware.
Ha! just looked and saw that SIP sells the EK rods now.
great.
will be interested to see how you find the EK's.
Hope they catch your order.
Keep us posted.

I'm still thinking I'll go with a PWM 38 for my my reeded MHR 228 build, but might also look at a smart carb since it's nothing but a budget sheet for the next stage of the build at the moment.

Looks like folks have already covered most of the basics of resources and how to use them, so I won't repeat them, but mostly just wanted to chime in and say that I'm here for this

So, got the EK-28 metering rod and put that in and changed the carbs over.. first impressions were that it was much smoother that the EQ series rods. Still haven't had a chance to do a bigger ride on it as the weather has turned bad and half way through a disc conversion now. I've also order a PWK 35mm and am keen to try it but all in all the SC is pretty smooth.. might have to upgrade from the 28mm though.. maybe a 36mm is in order??!!


the SC fits really nice with the malossi air bellows... if I end up going 36mm SC, I'll have to get the dumbo I suspect.

Half way through the disc conversion, crimaz master cylinder and just a standard grimeca caliper.. that has to be better than the drum that was on there :)