PWK United Kingdom source

[jseng1]

After trying the Keihin FRCs, The Keihin CRS smoothbores, Dellortos - all these carbs are big, are a tight fit or something or other that makes them short of perfect and most have a stiff throttle pull (or two cables for the FRC). Amals don't last. The Keihin CRS is the closest to being perfect.

But the little PWK (when dialed in) is the only one that does everything, has a light throttle pull, is small, stays tuned and pulls as well as the expensive Keihins. So after all that I went back to the PWKs on my own personal ride. But I won't sell em anymore.

 

[no750]

We used them on my grandson's junior speedway bikes for a while. The quality is questionable they wore out quickly and jets and needles came without ID numbers.

are you sure you talk about wassell evolution carbs, which are comparable to the amal premiers or do you refer to the ordinary type?

 

[crusadersports]

Here's the specs to set up the PWKs

32mm PWK

Use only Special PWK needles #P11/32 available from JRC

start with130 main jet

Drill needle hole in slide to .120”

.101 needle jets 2nd needle position, or 102 needle jet with clip at top

#38 idle jet with idle mix screw approx 1/8 to 1 turn max. Change idle jets if necessary (usually smaller).

Bend brass tube inside float bowl to clear float, shake when assembled to make sure float is loose,

check idle bypass jet is clear (.016”),

Stretch idle mix and idle speed spring for more tension

drill hole in side of main jet tower to 3/32 for more fuel flow

Use 8JS float needles (from JRC) or file the 4 corners off the float needle ridges near the rubber tip so it won’t hang up.

FLOAT LEVEL - Hold the carb upside down at a 45 deg angle so the pin in the float needle doesn’t compress. The float should be 3 to 4mm below the top of the central casting or lowest part of the aluminum carb body (not the main jet or the hex shaped main jet holder).

Use aircleaner K&N RC-2380

**********************************************************

Some people couldn't tune them. I asked them to return them for testing. I put em on by test bike and they tuned & idled perfectly. After sending them back the same people still could not tune them even though they could tune Amals (PWKs have subtle tuning characteristics). So I gave up on them and went to Genuine Keihins which tune very easily.

Keihin CRS 31 & 33mm smoothbores are worderful but they require a lot of modification to fit a Norton. They are a tight fit.
Keihin FCRs are also very good but they are physically huge, look a bit weird and the slides rattle and make the same sound as detonation. You can't get them smaller than 35mm and they are a very tight fit.

Amals and PWKs are the only small body 30 to 32mm carbs that will fit a Norton well and look decent. The PWKs will blow away the Amals performance wise (flat slides) and they stay tuned - but only for those who have an ear for tuning carbs. They require all the modifications mentioned above to work on a Norton. They don't work for people who try to tune them the same way you tune Amals. When I first starting dealing them they came from JRC with the "OKO" brand name milled off and the bell mouths remachined and that fooled me for awhile. They are Chinese knockoffs of a 28mm PWK carb body but enlarged to 32 or 34mm throat with two screws holding down the top lid instead of the original style PWK screw top.

If the PWK idle mix adjustment makes no difference at all from closed to 1 turn (too rich even after changing to smaller idle jets) then the idle jet body tower is defective - about 1 out of 100 carbs can have this problem.

Jim, Did you carry out all these mods on the 100 sets of PWKS you sold, or is this something owners of those carbs (me included- they are still in a box waiting for me to build the 920 I bought them for) need to do for themselves ?

 

[jseng1]

Yes I carried out all the mods on every carb I sent out. The setup info that I provided on page one of this thread is for those who want to buy the carbs directly from the supplier and make the mods themselves. You must have the custom needles from JRC for them to work.

Here's the instructions:

And the PWK specs/modifications again:


32mm PWK

Use only Special PWK needles #P11/32 available from JRC

start with130 main jet

Drill needle hole in slide to .120”

.101 needle jets 2nd needle position, or 102 needle jet with clip at top

#38 idle jet with idle mix screw approx 1/8 to 1 turn max. Change idle jets if necessary (usually smaller).

Bend brass tube inside float bowl to clear float, shake when assembled to make sure float is loose,

check idle bypass jet is clear (.016”),

Stretch idle mix and idle speed spring for more tension

drill hole in side of main jet tower to 3/32 for more fuel flow

Use 8JS float needles (from JRC) or file the 4 corners off the float needle ridges near the rubber tip so it won’t hang up.

Also you will need a special idle mix adjustment screw with a longer head on it from JRC. I would cut a slot in the head and soft solder a short wire in the slot so I could reach in between the carbs to turn it for adjustment.

FLOAT LEVEL - Hold the carb upside down at a 45 deg angle so the pin in the float needle doesn’t compress. The float should be 3 to 4mm below the top of the central casting or lowest part of the aluminum carb body (not the main jet or the hex shaped main jet holder).

Use aircleaner K&N RC-2380

 

[74ok]

After trying the Keihin FRCs, The Keihin CRS smoothbores, Dellortos - all these carbs are big, are a tight fit or something or other that makes them short of perfect and most have a stiff throttle pull (or two cables for the FRC). Amals don't last. The Keihin CRS is the closest to being perfect.

But the little PWK (when dialed in) is the only one that does everything, has a light throttle pull, is small, stays tuned and pulls as well as the expensive Keihins. So after all that I went back to the PWKs on my own personal ride. But I won't sell em anymore.

hmmm?? must be a good reason

 

[jseng1]

hmmm?? must be a good reason

As I said in post #16:
Some people couldn't tune them. I asked them to return them for testing. I put em on by test bike and they tuned & idled perfectly. After sending them back the same people still could not tune them even though they could tune Amals (PWKs have subtle tuning characteristics). So I gave up on them and went to Genuine Keihins which tune very easily.

PS
It takes a good ear and some learned technique to tune these carbs. This vid may help:

 

[Brooking 850]

I have a set of Jims PWK's on my roadbike , they have been on the bike for 5 years and after some initial idle issues which I found under the tower in the casting, they run really well.
I have since purchased 2 x sets from guys who couldnt tune them and so have a couple of spare sets.
There did run a bit rich and I have dropped a main jet size.
I have also drilled the front side of the carb throats and installed a balance tube, this also allows the use of vacuum gauges for testing and tuning.
These are on a standard RH4 head with a clean up in the ports .
I have just done another fuel milage test on Sunday, rode at 70mph where I could, lots of fast hilly twisties and they still return 54mpg at those speeds and hard hill work. Thats 19+ km/l.
Cruising at the speed limit and no hard throttle use will return 60+ mpg.
Under the tower Jim is talking about is a super fine hole in the idle circuit , this hole was irregular due to casting imperfections, once this fine hole was cleared and the edges made round, this sorted the idle problem.
As Jim said, the idle/mixture set up is quite fickle that puts people off if they are used to tuning AMAL's.
I use a Gunson tuning tool to get those mixture right at 1500 rpm.
http://www.gunson.co.uk//product/G4171
Regards Mike

 

[crusadersports]

I have a set of Jims PWK's on my roadbike , they have been on the bike for 5 years and after some initial idle issues which I found under the tower in the casting, they run really well.
I have since purchased 2 x sets from guys who couldnt tune them and so have a couple of spare sets.
There did run a bit rich and I have dropped a main jet size.
I have also drilled the front side of the carb throats and installed a balance tube, this also allows the use of vacuum gauges for testing and tuning.
These are on a standard RH4 head with a clean up in the ports .
I have just done another fuel milage test on Sunday, rode at 70mph where I could, lots of fast hilly twisties and they still return 54mpg at those speeds and hard hill work. Thats 19+ km/l.
Cruising at the speed limit and no hard throttle use will return 60+ mpg.
Under the tower Jim is talking about is a super fine hole in the idle circuit , this hole was irregular due to casting imperfections, once this fine hole was cleared and the edges made round, this sorted the idle problem.
As Jim said, the idle/mixture set up is quite fickle that puts people off if they are used to tuning AMAL's.
I use a Gunson tuning tool to get those mixture right at 1500 rpm.
http://www.gunson.co.uk//product/G4171
Regards Mike

That's great feedback, Mike, thanks for posting. Mike (or Jim), would it be possible to post a pic of that tower and the super fine idle control hole for reference ? Sounds like it is well worth a close look. And btw I get 55-60 mpg out of the single Mikuni on my Mk3, and I bet yours doesn't run out of puff at 80 mph... these do sound good carbs if you have the patience to set them up. Mike, what sort of mileage have you done in those 5 years and have they needed much adjustment once set up?

 

[74ok]

did read 16 but wasn't clear to me that was the reason tx

As I said in post #16:
Some people couldn't tune them. I asked them to return them for testing. I put em on by test bike and they tuned & idled perfectly. After sending them back the same people still could not tune them even though they could tune Amals (PWKs have subtle tuning characteristics). So I gave up on them and went to Genuine Keihins which tune very easily.

PS
It takes a good ear and some learned technique to tune these carbs. This vid may help:

 

[jseng1]

This is the hole that needed clearing according to Brooking 850
Photo by Mike.

 

[crusadersports]

Oh blimey! Easily missed then... Thanks for posting Jim. What would you advise for the best method of checking that passage is clear?

 

[Brooking 850]

Crusader, there are three holes under the tower, 2 x superfine ones either side of the bottom of the slide and one larger one.
They are easy to spot as under the tower base there are 3 x small O rings attached to the bigger O ring and seal around these holes.
I used a bristle off a wire brush or a superfine gas welding tip cleaner.
Mine had casting imperfections and once cleared then became round at the opening edge.
Hope this helps
Regards Mike

 

[crusadersports]

Crusader, there are three holes under the tower, 2 x superfine ones either side of the bottom of the slide and one larger one.
They are easy to spot as under the tower base there are 3 x small O rings attached to the bigger O ring and seal around these holes.
I used a bristle off a wire brush or a superfine gas welding tip cleaner.
Mine had casting imperfections and once cleared then became round at the opening edge.
Hope this helps
Regards Mike

Thanks Mike, that's really helpful. A bristle from a wire brush is a brilliant idea. Does the passage turn any corners and can you see the bristle poking out the other end so it's certain it is clear?
Still like to hear if these carbs have needed any/much maintenance in the 5 years you've had them on your bike and what sort of distance you've done in that time if possible Mike? Have you found they stay in balance?

 

[xbacksideslider]

Once I was done fiddling, I left them alone, no reason to touch em. That was five years ago, if not more. Even our California 10% ethanol gas doesn't seem to bother em.

 

[brendanq]

So one would assume a decent dyno shop could make any changes and getting it running sweet and like others you wouldn't have to touch it all that much again.

also steadfast motorcycles in US sell them on eBay, anyone have any ideas if they have had the mods done to them?

 

[jseng1]

brendanq - No one will supply them with the necessary mods or the correct needles. Its "do it yourself". See all the mods/specs in post #24. The necessary special parts are available from JRC in the US. They are the only ones who have the correct slide needles and float needles.

Mikes XS used to sell them, not sure if they still do.

Correction - early sets I sent out did not have the correct 8JS float needles because this problem did not show up at first and had to be addressed.

 

[Jagbruno]

brendanq - No one will supply them with the necessary mods or the correct needles. Its "do it yourself". See all the mods/specs in post #24. The necessary special parts are available from JRC in the US. They are the only ones who have the correct slide needles and float needles.

Mikes XS used to sell them, not sure if they still do.

Correction - early sets I sent out did not have the correct 8JS float needles because this problem did not show up at first and had to be addressed.

Dear Jim,

https://www.aliexpress.com/item/New...a1c4-4e6f-b7ed-49e19d5f50a7&priceBeautifyAB=0

Are those the same type (albeit copies) than the one you are (were) using? Do you have any experience with these? What, in your experience, would be the optimal size for a 850 Mk2a with PW3? 32, 34 or 36mm?

Thanks a lot in advance!

Bruno

 

[jseng1]

I don't know if they are identical - I've never bought those. Those are unbelievably cheap. I sold more of the 32s than the 34s. I have no experience with the 36s and they may be a larger body. The 34s were pushing the dimensional limits already and the slides etc were not the same as the 32s.

They will not work without the correct needles and other mods as listed on page 1 of this thread in post #16

Also you will need a special idle mix adjustment screw with a longer head on it from JRC. I would cut a slot in the head and soft solder a short wire in the slot so I could reach in between the carbs to turn it for adjustment.