keihin pwk 32 with 750 big bore

[chrispunk]

hey all, so i just ordered a set of 750 barrels for my chop project. ive got a set of pwk32 i was going to run. does anyone have any tips or a good starting point jet wise?

itll have open pipes and some kind of clamp on airfilters

thanks

 

[XSLeo]

Are those the ones Mike's XS sells? most of us on here will tell you to put them on a shelf and get good carbs. The Ninja ex500 are a good carb.
Leo

 

[chrispunk]

i got em of a guy on one of the fb groups but im pretty sure they originally came from heiden

 

[XSLeo]

I might try them as they are and see what happens. Test them for WOT response to get main jet right then work down from there.
Leo

 

[grizld1]

First off, welcome,Chris. Next, please accept my condolences. I'm very sorry to tell you that whatever you paid for those carburetors, you paid too much. There is not and there never was a 32 mm. PWK carburetor produced by Keihin. Three facts: The PWK is a dedicated 2-stroke carburetor. Keihin for some reason produced only one needle jet (AKA atomizer, AKA emulsion tube) for each venturi size in the PWK series. 2-stroke motors require needle jets that are much richer than a 4-stroke motor requires.

Years ago a hack at JRC Engineering in the USA had the bright idea of having cheap knockoffs of the PWK28 bored out to 32 mm. to get a smaller needle jet that would get closer to the requirements of British 4-stroke twins. The carbs were badly made and caused trouble, but a lot of them were sold because they were cheap and because guys didn't know enough to question JRC's very effective advertising.

Jerry Heiden and Mike Lalonde noticed that item and started selling the same thing. Because of outing by a few folks who knew the difference, Lalonde and Heiden started having the knockoffs made without the Keihin brand name. When enough complaints had been voiced about quality issues, they started using authentic Keihin PWK28s punched out to 32 mm.

But that did not resolve the underlying problem, which is that while the carbs can be tuned well enough to let a 4-stroke motor run, the needle jets are still too rich--and yes, they're still too rich for a 750 cc. 4-stroke motor with a free-breathing exhaust system, etc. Why does this matter? Because the NJ is the primary metering component in the cruising range of the throttle, and you would do very well to go 36 miles on 4 liters of fuel with bored out PWK28s. So here's the choice. Pay now for workable carburetors, or play with the PWKs and, if you're successful in making them work, pay later in fuel costs.

The use of genuine Keihin carbs put the price very close to the price of the Mikuni VM34, which can be tuned very effectively for our application, so Mike's XS and Heiden Tuning have both stopped selling the modified PWK28. Mike's has started selling VM34 kits, and I think Heiden has done the same.

If you want to have a go at tuning those carbs, mrriggs wrote a very detailed thread on the process a few years ago. Look around and you'll find it.

 

[chrispunk]

hey grizld1, thanks for the info,

it seems heiden are definitely still selling them. http://www.heidentuning.com/p/28/3151/mo74-cg|25=9/#48-14900-xs-performance-keihin-carb-kit- im kind of disappointed if they are as bad as you say as i thought heiden where pretty respectable.

ill check out that link, and i should really start a build thread.

 

[grizld1]

Interesting; awhile ago I could only find parts for those carbs listed on Heiden's site. Chris, I don't expect you to read what I posted and assume that it's correct. Run some searches here and elsewhere for reviews.

Re. Heiden, I think he ran a better operation before he started collaborating with Mike Lalonde on the XS Performance product line of Chiwanese junk. I wasted money on the "XS Performance Billet Camshaft" myself a few years ago; the grind is good, a clone of the Megacycle 250-00. But the design is a mess; I could time the thing either by trusting two 7 mm. screws to hold the sprocket while it's mounted on a pair of slots (standard for adjustable cam sprockets is 3-point mounting), or mount the sprocket stably on a pair of holes and time it by adjusting deck height. And once that was done I discovered that the pair of heavy, imbalanced lugs that hold the screws and swap places with every rotation of the crank made my motor vibrate hard enough to shake the fillings out of my teeth. I reinstalled my Shell #1 cam and gave the XS Performance item to a friend to experiment with. He offered money and I refused to take it; as far as I was conceerned it wasn't worth more than scrap value. BTW someone tried to correct me once by claiming that the mounting screws are actually 8 mm., so Heiden may have changed the specs some time in the last 8 years.

Anyway, as you look around, you'll start to notice that entirely scrupulous vendors of performance parts don't tend to claim that this bit increases power by so much, that bit by so much, etc. When you see that sort of thing enough you'll start to recognize it for a red flag.