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PWK Carb Adjustment on a 1000SP

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Ratso88:
The PWK is a 2 stroke carb.
It can be made to work on a 4 stroke but will never be optimal.
It’s just not designed for it.

The FCR would be a much better choice.

It is what you have and if you’re satisfied that’s what’s important.

Antietam Classic Cycle:

--- Quote from: Ratso88 on April 29, 2025, 06:31:47 AM ---The PWK is a 2 stroke carb.
It can be made to work on a 4 stroke but will never be optimal.
It’s just not designed for it.

The FCR would be a much better choice.

It is what you have and if you’re satisfied that’s what’s important.

--- End quote ---

Steadfast Cycles sells a kit with PWK carbs to replace the Amals on Triumphs and Nortons:
https://www.ebay.com/itm/204487499347

The late Mike Tiberio was among the first to adapt these to a Guzzi using manifolds from an Amal equipped Eldorado. Mike being a racer was a stickler for proper jetting and running. His setups worked perfectly well - better power than the VHB, and equal in fuel economy. Sounds like they were "optimal" to me. I have  the same setup to use on an upcoming project.

Here's Mike's write-up on the conversion:

I have been posting about this on the loop list, but I should really spread the
news. I have been looking for a replacement for the old square slide VHBs for a
while. I found a chinese made Keihin carb knockoff modified to replace british
Amals. Mating a pair of those with a set of the Guzzi Amal manifolds (yes small
valve roundfins came with Amals for a while in 1974 I believe) is possible and
practical. Other than buying the manifolds, the carbs, and a pair of off the
shelf throttle cables, the whole conversion required no machine work or other
special fitting or cuttin (other than fuel line)...

I have never installed a totally different carbs on a bike and had them work as
perfectly as these carbs did tonight on my Eldovert. It all jelled when I got
some throttle cables in from MG tonight. I asked the guys at MG to measure the
freeplay of their throttle cables, and asked them to send me a pair of whichever
ones had the most freeplay. It ended up being their "no name throttle to VHB"
cables. I knew the Keihins ate up more cable than the VHBs so I
thought I'd start with these cables. As I was doing some measuring tonight
trying to figure out how much I was going to modify the cables, I realized they
would work with my Thom 2C throttle and the Keihins as delivered. Then I
realized I had everything I needed, and by 8:30 I had them installed. I went to
start the bike and it didn't even cough. Oops, I left the spark plug wires off
(I removed them to get them out of the way). Once I had spark, choke, the bike
started right up and settled into a decent idle. I rode off down the street, and
by the time I went 3 blocks, it was idling high, oops I left the chokes on.
Chokes off and it idled perfectly, and ran great in my residential neighborhood.
Quick to get home, finish buttoning up the tank bolts and put the saddle on, get
my jeans on and head out for a top speed run. Bike pulled cleanly to 100, and I
ran out of road. I'll have to watch the gas mileage, and do some plug chops to
get these carbs any better set up they are that close. I uploaded some pix so
you can see the sano install with the Guzzi Amal manifolds...



They have carb mounted chokes, but a cable kit is available, I might spring for
that. They take 1/4" fuel line, but since I was set up for filters that take
1/4" line, that issue was no sweat. I was using dual spigot banjos on my VHBs
for a crossover, I'll either have to "T" each line to do the same or use both
petcocks. I do have a set of Tonti petcock adapters, so that will give me a
reserve back if I don't go for a crossover. The inlets are about 2" dia, so I'll
probably pick up a pair of unifilter foam socks to handle the air cleaning
chores. There are no clearance issues between the float bowls and the bell
housing. In other words, a bolt on perfect fit as long as you have the Amal
manifolds... Oh yea did I mention the throttle pull is oh so much lighter...

More later...

The carbs are made by a Brit Bike specialist called JRC Engineering
(http://www.jrceng.com/). They are "Keihin PWK" oval bore (28/30) semi flat
slide carbs. They are big with the moto cross crowd. JRC doesn't do retail, and
has dealers. I used Specialty Spares 253/853-1420. They were $100 a pop plus $15
shipping. The manifolds were made by Moto Guzzi to allow mounting of Amal carbs
to Eldos back in the early to mid 70's (either Dell'Orto couldn't supply enough
carbs to Guzzi, or Guzzi didn't pay their bill!?!). No one ever liked the amals
on guzzis, so the manifolds are easy to find used. While a lighter throttle pull
is one reason to convert, I was hoping for more precise metering and
adjustability, together with a sense of lets do this because we can...


Dec. 5th, 2011

Still on the bike. All I did to jetting is go one smaller on idle to 35, and lean out the ims to 2.25 turns off seated. 37 to 39 mpg with my convert.

still occasionally pops, but then so did the vhb's. Bike does have 155000 miles, so I don't expect perfection. Throttle spring is soooo much lighter. Like FI. I recco this mod to anyone that has 29 or 30 mm vhb carbs...

monkeyodeath:
Having better luck with the carbs, but I'm noticing a "gurgling" sound coming from the left cylinder area when I shut the engine off. Does anyone know what this might be?

Ratso88:
It’s interesting that someone has picked up on the PWK knock offs for use on a four stroke.
I guess they can be adapted and made to work and do the job, better than a 50 year old Dellorto.
It’s definitely worth a try. Especially at the price it’s being offered by Steadfast.

I do prefer the Keihin over the Mikuni.
I run the PWK Air Striker on my race bikes, all two stroke 250 and 500.
I’ve run the FCR on a DR650 build and it made a huge difference  over the stock CV.

I hope you can get your SP sorted out, seems promising.

steven c:
 I have an Eldo with AMALS  but with a convert motor in it, I was thinking about trying these but it has been years since I read about them. Having said that I have had no issues with the Amals, bike has always run okay. I just thought maybe they would give a little more zing to it.

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