by Warkton Tornado No.1 » Fri Sep 30, 2022 11:32 am
That's not an easy question to answer. All that I can do is to try & state my own experiences.
Years ago, I took a punt on a licensed PWK made by OKO secondhand from a parts-fair for a tenner which I loaned out to WT No.2 who subsequently bought into the PWK ethos with a 34 mm Chinese knock-off. TBH it ran incredibly well, even better when I'd blueprinted it & procured the smaller pilot jets necessary for a mildly tuned 200 running a DIY foam filter. However, as these carburettors definitely 'fight above their weight' he fitted another 30 mm bootleg with no perceptible loss in performance. IMHO these carburettors are that good that the venturi size is not hyper-critical & they will deliver well if the time is taken to set them up, which is not difficult. For the record, I've used pilot jet sizes down to 32 on piston port engines & in the 50's for reed valve cylinders.
Despite my personal findings that the Chinese copies that my mate acquired are by no means shabby, & assuming you want the smaller sizes, I'd still be inclined to go for Koso, OKO, Stage6 or (new to me) ZSDTRP though it is notable that Polini have bought into the concept. In fact, currently 20 quid gets you an unused ZSDTRP 32 mm PWK on eBay & I'd have no misgivings about the choke size being too big.....
I hope my response somehow helps but the question is a bit open ended. I'm happy to elaborate on needle, main jet & what I think of power jetting.
As for Keihin, undoubtedly the larger sizes are highly rated elsewhere & I have an untested 39 mm. But they have a major shortcoming. They do not have a replaceable needle jet/atomiser so when that wears, the whole carburettor is worn. I see that as a challenge & hope to prove that an atomiser from another manufacturer will be persuaded to fit, precisely as I've done to an old VHB in converting to two stroke.