PWK32 synchronising.

[Tim L]

Hi all,
I have just bought a pair of the Keihin PWK32 carbs from the XS650 shop.
The bike starts straight away which is good but I am looking for a 'best practice' option for synching the carbs.
I have synched by measuring and synched by vacuum gauge but their is a lot of fluctuation on the needles and the carbs seem to react to throttle position changes differently even though they are synced.
I have got an electronic ignition and dual output coil so don't want to run it with one spark plug disconnected just in case.
Has anyone got a fool proof way for setting them up.
Something else I was wondering. Should the carbs be linked by a balance line. On my Moto Morini 350 the carbs are not a linked pair, same as the PWK's on the XS, but they do have a balance line linking the carbs together.
Many thanks.

 

[bosco659]

I’ve been messing with my PWK’s for a week now with various issues. Synchronizing the carbs is pretty easy.

First I make sure both slides are closing complete all with the idle adjustment screws backed all the way out.
Next I make sure the cables are routed properly.
Make sure both slides open to wot
Take the majority of the slack out of the cables. I stick my finger inside the cab and move the adjuster until I can just feel the slide start yo move then turn it back in 1/8 of a turn to leave a bit of slack.
Hook up vacuum gauges. I assume you have a pair of them.
Warm up the bike.
Adjust mixture screws to get cylinders firing smoothly.
Looking at the gauges adjust idle to desired speed then using both screws get equal vacuum readings on gauges. If needles are bouncing, close the attenuators to stop major fluctuation of needles.
Once idle is stabilized, hold throttle at 3,000 rpm and adjust throttle cables to achieve equal readings on both gauges.
I have done this with vacuum gauges but found a manometer style device more accurate readings

That’s how I do it. Maybe others will have a different or better method. Hope this helps.

 

[Tim L]

Thank you bosco659.

 

[5twins]

Yes, syncing carbs with individual cables is a two step affair. They must be synced at idle and "at speed". When you adjust the idle speed screws, they raise or lower the slide slightly. This adds or subtracts some freeplay to/from the throttle cable, and that can throw off your "at speed" sync. For that reason, you must do the idle setting and syncing first. Then you can do the "at speed" syncing which basically means matching the freeplay on the two cables.

 

[Tim L]

Thank you 5 twins.
I need to work out the best way to sync the idle speed screws.
Doing it one side at a time is the best way I guess but don't want to unplug a spark plug and damage the electronic ignition.
I was going to just switch fuel off to one side and then let that sides float bowl empty while the engine is running.
Someone said remove the rubber bung from the barb on the inlet manifoild but that could just weaken the mixture while the cylinder still does some work affecting the set up.

 

[5twins]

I've always used a manometer, don't care much for the vacuum gauges because of the way they bounce around. I never did the one cylinder running method, what they call the "dead cylinder" method.

 

[RC4MAN]

You either need inline restriction orifice or an inline needle valve to each gauge or you will get gauge bounce.
I have two sets of gauges, one purchased from Honda parts back in the 70's, each threaded fitting has a small damping orifice in it, the other set is a homemade rig an older friend made and gave to me when he got out of bikes, he used small needle valves in each line to dampen the pulses.

 

[chew6520]

This works for me with PWKs on my Triumph. http://www.jba.bc.ca/Bushmans Carb Tuning.html

 

[Tim L]

I finally got around to trying to synchronise the carbs today. Didn't go to well. I would wind the idle screws in a bit and start the engine, run it to warm up a bit then try to reduce down towards a decent idle speed while matching the readings on the manometers. Trouble is, every time, the idle sat at 3000 while I adjusted then dropped off to around 800 quite rapidly and the engine stalled. I am pretty sure the slides are moving freely. I was using 2 temporary fuel supplies so maybe there was an issue there. I will give it another go when I get my tank back.

 

[5twins]

Those PWK's can be a questionable carb. They sometimes have manufacturing issues due to lack of quality control. Sometimes the internal parts like the slides and floats don't fit right and hang up or stick. Sounds like maybe you're dealing with some of that. There was a very knowledgeable and skilled member here a few years ago who tried to get a set of those working right. He spent like a month and several hundred dollars to no avail. He finally threw the towel in and got different carbs, lol.

 

[Tim L]

I do have the original CV carbs. When I priced up all the parts I needed to make them good I realised that I would have to sell a vital organ so opted for the PWK's as they seemed pretty good for the money and people had said they were not too bad. Maybe I do need to sell that kidney and re-build the CV carbs.

 

[Tim L]

Reading another forum I see there may be a chance that my slide is not closing fully due to vacuum in the intake manifold. Maybe I need to fit a stronger return spring for the slide. Does anyone know if stronger springs are available?

 

[bosco659]

Welcome to my world of messing with the PWK’s. I got mine in sync a number of times but every time I work on them (which seems to be a lot) they go out of sync and the long process begins again. The other pita is that to adjust the throttle cable length, it’s 10X easier to do it with the tank removed. That necessitated the setup of a remote fuel tank that I could still drive the bike with.

I too have experienced the sticking slides, but usually when I’m riding. Happens randomly when shifting or letting off the throttle to idle at a stop. I’ve stretched my springs but that didn’t help much if at all. I think it may be vacuum related because they don’t seem to stick in the bores when assembling / disassembling them.

Most of the work I’ve done on mine is related to mixture and idle performance. I had issues with the right cylinder running so lean that it wouldn’t fire at idle. Yet if I pulled the plugs it was sooty and black. I’ve checked all ignition related components and believe all issues are fuel related. I’m trying to buy different needles to try but am having difficulty sourcing them here in Canada.

I think the PWK carbs are crappy in the following areas: the cable guide in the cap of the carb doesn’t thread in precisely and lacks a jamb nut. That allows the cable to move and the slightest movement throws off the sync. Second, on my bike, the 45 degree cable guide doesn’t provide a straight pull on the cable. The cable sits in an awkward angle in the socket of the guide. I wanted to try to bend them but was worried that I’d break them. If I could buy replacements I’d give that a try. Mixture screw access is a pita for the right carb.

Did you set your float height? What did you set them to? I searched quite a bit and couldn't get a definitive answer on the spec so mine are set at 22mm yet most info available says they should be at 19mm (impossible on my carbs).

I haven’t given up on them yet but if I get frustrated enough I may buy a set of Mikuni’s. Just concerned that if I do, I’ll have similar tuning issues and my wallet will be a lot lighter . One thing I must keep in mind is that this is a 44 year old bike and maybe my expectations are too high for the way it runs? I’ll still work on it for a while and hopefully I can get it running half decent and just ride the bike accepting the less than perfect running.

 

[5twins]

I have two 650s with stock carbs. One has the BS38s, the other the BS34s. Both run well, start easy, will sit there and idle all day long if you let them, rev from idle to redline with no spitting, balking, stumbling, or break-up. These can be very nice running bikes.

On the BS34 equipped bike, the P.O. said he always had carb issues. When I went through them, I could see he tried but he didn't go far enough, he didn't go all the way. I found a couple of the butterfly plate screw heads buggered so it seems he couldn't get them out and change the butterfly shaft seals. He also didn't pull the mix screws and renew their o-rings. After I managed to do both those things, the carbs seem to be working just fine. As is often the case after cleaning dirty carbs, I have had a couple things plug back up, requiring me to go back in and re-clean some items (right carb pilot jet, left carb choke jet).

 

[Tim L]

Hi bosco659,
My XS came with a set of BS38's but they needed new floats, diaphragms, jets........well pretty much everything really. When I priced up the parts they would have been more expensive than the PWK32's so that is what I bought.
Needless to say I started cleaning the BS38's this afternoon and am doing a list of parts I need.
With the PWK's the bike started okay. I wound the idle adjust screws in a bit to give me a decent idle. Probably too much at about 3000 RPM. As I wound the idle adjust screws out nothing happened until I had wound both out a fair bit and then idle dropped to around 800 and the engine stopped.
It would appear to be a slide problem although if you rev the engine using the throttle and then close the throttle the revs drop straight off.
I spoke to Jerry at Heiden Tuning this morning and he is going to send me some heavier springs. When they arrive I will take the slides out, clean them again and lightly oil them then fit them back in with the heavier springs. Then try to synchronise the carbs again.
Allens Performance are Keihin dealers and they have never heard of a PWK32. It doesn't exist apparently.
Interestingly, Heiden Tuning stopped selling those particular carbs a couple of years ago. Make of that what you will. If they were any good he might still stock them.
My cable adjusters came with lock nuts and I don't think there are any problems with the cables or adjusters.

 

[Hudriwudri]

Hi there,

Real Keihin PWK's or Chinese copies?
The Chinese copies have supposedly a ton of issues.
It seems to me a lot of people nowadays don't use anymore the dellortos, why is a mystery to me.
Wonderful carb, and as 36 it is a straight fit in the Sr manifold and the Sr manifold ist a straight fit on the xs head, in particular if you get the restricted 27hp carb rubber from Europe, which has a rubber restriction which is perfect for grinding to your port needs.

I have on a lot of my bikes dellortos and I love them for their simplicity and spare part availability.

Kind regards

Christian

 

[bosco659]

Don’t know if they are knock offs or not. There are some things about them that suggest they might be like poor machining and sloppy fit of pieces like the cable guides.

 

[Tim L]

So my stronger springs for the PWK32 carbs arrived from Heiden Tuning. They are definitely heavier but they are also about 0.5mm wider overall so don't fit in the slide properly. I cleaned and lubricated my slides and put the original springs back in. Tried to synchronise again. Just the same as before, almost impossible to get them synched so I took them off and will be putting the BS38's back on once they are cleaned and re-built. On nights at the moment so won't get round to that until Friday.

 

[bosco659]

Too bad the springs didn’t fit. My carbs are fairly well synced at idle and at cruising speeds over 3,000 rpm. Still running rich as heck at idle but I’ve learned to live with it. My slides do stick randomly and I put up with it as well. It hasn’t become a safety issue so I’ll leave it alone for now. Still messing with different jets and needle heights. Pretty sure I’ll go for a set of Mikuni VM34’s for next season. I don’t think I’ll ever get the PWK’s running perfectly (as many others have already advised they aren’t the best).

 

[grizld1]

Tim L, what your Keihin dealer told youis correct. Keihin does not and never did make a 32 mm. PWK carburetor; after 30 mm., Keihin sizes its venturis in odd numbers.

What you have is a knockoff of the PWK 28 with the venturi bored to 32 mm. (How do I know it's a knockoff? Keihin slides don't stick, and a pair of Keihins will cost much more than components for rebuilding a pair of BS38s.) The reaon for this practice is that Keihin designed the PWK with only one needle jet size per carb venturi size, and the firms that copied them did the same. The PWK was designed by Keihin as a dedicated 2-stroke carburetor, so to get a lean enough NJ for 4-stroke use, the 28 mm. carb body had to be used. We can blame JRC Engineering, an American supplier of Brit bike parts, for coming up with the idea. Mike Lalonde and Jerry Heiden noticed the product and the profit margin and sold the same junk with more hype and bluff. Sorry for your pain.