But as I previously mentioned, I have run the PWK in a stock manifold and it worked fine.  Just need a clamp with more range.  I'm also pretty sure the HS42 manifold you ordered will work fine too.  It's a lot beefier than a VM manifold.

I asked about your tire and gearing because they affect your odometer reading.  Since the lion's share of my testing was done with stock gearing and a stock rear tire, the mileage numbers I was posting are "Savage Miles".  If you put on a larger rear tire or a 25 tooth pulley or both, you are not registering the correct mileage on your ODO.

If you just have a 140/90 Dunlop 404, you should correct your ODO reading by 1.046 before you calculate fuel mileage.  For instance, if your ODO indicates you went 100 miles you actually went 104.6 Savage Miles.

If you are running the 140/90 Dunlop 404 with a 25 tooth front pulley, you should correct your ODO reading by 1.138 before you calculate fuel mileage.  So if your ODO indicates you went 100 miles you actually went 113.8 Savage Miles.

If you are running a 140/80 IRC tire with the 25 tooth pulley, the correction factor is 1.092.

Correcting the ODO reading will improve your mileage numbers a bit,  but at your current 40 mpg the refined calculation will still be too low.  Your fuel mileage seems way too low.  Perhaps when you get the manifold and jetting squared away the fuel economy will be there.  I've got a big motor with an inefficient pop-top piston and I never see anything less than 56 mpg.  It's almost always in the low 60s.

Hi Mike. I'm going to send a series of photos.  I'm waiting on jets, manifold, and clamp - so I wanted to get these out for observation and diagnosis in case there is something else weird before I start tinkering.  First photo shows evidence of air/fuel bypass at the clamp area.  I have 2 more photos of the other sides and they show about the same amount of bypass.  I have a strong suspicion this is why I have to 'jet up' so big to get the right air/fuel mix and poor MPG.  I think I'll just try the new clamp without the new manifold.

Inside diameter of air horn side as best as I can manage holding the carb, camera, and meter.  OD measures about 63mm which matches the product description in the ad when I purchase.  The air horn is about 6mm wider ID and OD than stock.  I fabricated a piece of 2.5" ID (almost exactly 63mm) automotive turbo tube to connect the carb to the box.  It fits great at the air filter box and the carb with good tight clamps.

The jets and float and other good stuff...  It has a removable needle jet and normal Keihin main jets work.

A pic of the slide, spring, and cable contraption.  I'm not taking this monkey off the bike or apart if I don't have to!!  What a bugger to get it together right (F-BOMB city)!

New Mikuni 42 manifold just arrived.  It is very robust. Nice quality.  I buy from NicheCycle when I can.  Usually very good quality and I’ve had great results on little Chinese dirt bikes with their stuff.  I'm going to just hijack the worm gear clamp for now.  As you noted, the stock manifold has an o-ring and I really don’t want to break the seal at the head (it looks good the way it is).

Ms Bones.

Thanks Mike.  Interesting info on the needle jet.  I had no clue.  Flattening the curve…. That’s pretty cool old school!  How about richer at higher rpm’s when you wann stay cooler and leaner at low rpm’s?  

The mounting holes on the Mikuni manifold are larger and oval and not round.  I’m going to get some larger washers and change out the screws for hex heads.