Skip to content
Aussieveedubbers

Volume control screw

0 likes
Share Share on Facebook Share on X Share on Reddit
Log in to reply

REDKG Officially Full-On Dubber

327 posts · joined Aug 2002 ·

#22546
turning the volume control screw outwards on a 2Litre bus carby (twin solex) will have what affect, richer ?and what is its relationship to adjusting the central mixture and idle speed screws on the left carby?

vw54 Administrator Always Waiting 4 Friday

16,723 posts · joined Aug 2002 ·

#22553
Brian YES outwards is richer and more air in the case of the air idle screw.
I read it on FACEBOOK so it must be true


http://forums.aussieveedubbers.com/viewtopic.php?tid=91278&page=1#pid848630


http://forums.aussieveedubbers.com/viewtopic.php?tid=63561&page=1#pid624099


http://forums.aussieveedubbers.com/viewtopic.php?tid=4832&page=1#pid452603


http://forums.aussieveedubbers.com/viewtopic.php?tid=60650&page=1#pid574409

KruizinKombi Seriously Obsessed Cyber Dubber

3,493 posts · joined Aug 2002 ·

#22596
I wish someone would write a tech article on this. I've never understood carbies, least of all twin solexes. Then I can finally stop paying for tune-ups! 🙂
Kruizin Kol

aussiebug Officially Full-On Dubber

246 posts · joined Sep 2002 ·

#22702
vw54 wrote:Brian YES outwards is richer and more air in the case of the air idle screw.
Dave,

This is a little confusing. Are you saying that the twin Solexs on buses are the opposite to the Solexs used on bugs - with all of these (28 series, 30 series, 32 series and 34 series) the volume screw is an AIR volume screw, so screwing it out leans the idle mixture (ads more air) and screwing it in richens the mixture.

And just so there is no confusion about the adjusting screws, the larger bypass screw on the 34PICT/3 and H30/31 (bug carbies) adjusts the idle speed, but that's got nothing to do with the idle mixture.

Maybe I'm missing something....
Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.vw-resource.com

Phil74Camper Head in the Clouds

2,703 posts · joined Aug 2002 ·

#22794
Brian,

Here's a basic tuning procedure for twin carb (Type 4) Kombis.

Adjust the plugs, points and ignition first.

1. Setting each carb's idle speed

Screw in each carb's idle mixture adjust screw (on the side of each carb) until they contact the seat, then back off 2 and a half turns on each carb. Start the motor. Pull off the idle cutoff valve wire on one carb only, and note the rpm reduction. Reattach and repeat on the other side. The rpm loss should be the same. If not, turn the two mixture adjust screws in opposite directions to correct.

2. Mixture and Idle adjust

Reconnect all hoses and wires. Run the engine to operating temp. Now look at the left carb only - the large screw is for idle speed and the small is for mixture. Adjust the big idle speed screw until the engine idles at 900 rpm. Now turn the small mixture screw in until the idle starts to drop. Now unscrew it until until you get the fastest idle speed. Then readjust the big idle screw to get the idle rpm back to 900 rpm.

Twin carb Kombis don't use PICT Solexes...they are Solex 34 PDSIT2 and 34PDSIT3s. Left and right carbs are totally different and can't be swapped. The left carb 'controls' the right through the balance tubes and the air cleaner, which is why you only adjust the left carb (once all else is correct, of course)

KruizinKombi Seriously Obsessed Cyber Dubber

3,493 posts · joined Aug 2002 ·

#22931
Thanks heaps Phil.:thumb I've been reading the manual but didn't understand it :o but it is much clearer now. 🙂 I did read about the single idle circuit though, it's pretty clever! (Cleverer than I am!)
Kruizin Kol

REDKG Officially Full-On Dubber

327 posts · joined Aug 2002 ·

#23169
thanks for the info phil, seems simple enough for me. just got back from sunny melbourne. spent all day in the 'simulator' just across from a vw place at airport west but never got a break to check it out. will try adjusting carbys tomorrow.

KruizinKombi Seriously Obsessed Cyber Dubber

3,493 posts · joined Aug 2002 ·

#23213
Phil, my kombi dies when I remove either of the fuel cutoff solenoid wires, and I can't get it to idle below 1000 rpm. It usually chugs up and down between 1000 and 1300 rpm, according to two different tachometers. I've just done the plugs, points, tappets, etc. but it was running rough before-hand. What would you suggest I try next?
Kruizin Kol

Phil74Camper Head in the Clouds

2,703 posts · joined Aug 2002 ·

#24181
What a bugger!

When in doubt, I always go back to basics.

I'd remove the air cleaner and all the pipes and give the lot a clean. Replace the paper filter if need be.

Your jets might be a bit clogged, so if you have a spare weekend you could always unbolt each carb, take them apart and clean everything. VW shops still sell rebuild kits for Kombi Solexes (I think - I got mine from the 'states). They include all the gaskets and even nice new diaphragms for the accelerator pumps.

Assuming all the carbs are nice and clean, I would then check all the basic settings. With the choke closed, check the gap between the throttle butterfly and carb body. For 1800s it should be 0.7mm and for 2000s it should be 0.65mm. It can be adjusted with the nuts on the choke connect rod.

The adjusting screws in the carb bodies can be set to the factory default - all the way in then back out 2 and a half turns.

Bolt the carbs back on, and with the choke open screw out the idle adjust screws on each (on the linkage arms) until the throttle is fully closed. Then screw in until it just touches the throttle lever, then another quarter turn. Put your linkage back on and make sure it is nice and firm. Make sure the little springs and plastic locaters aren't missing. Turn the linkage and make sure both carbs start to open at the same time. Adjust if not.

Now set the mixture and idles as above, and it should run better. I've just paraphrased my pocket workshop manual, so when in doubt keep your manual nearby.

Good luck!

KruizinKombi Seriously Obsessed Cyber Dubber

3,493 posts · joined Aug 2002 ·

#24250
Thanks Phil, its always nice to have it said in non-workshop-manual-speak. 🙂

I've got the rebuild kits sitting on a shelf in my shed, so I guess I'm buying some carby cleaner this week in preparation for the weekend. I'll get all three kombi manuals out to make sure I have enough pictures of what I'm doing - I've always avoided carburettors in the past because they confuse me. :o

Does anybody know of it is possible to buy new balljoints for the linkages? (The little ones)
Kruizin Kol

REDKG Officially Full-On Dubber

327 posts · joined Aug 2002 ·

#24255
Phil, went to adjust carbys as per your instructions BUT, mine dont have the electromagnetic idling cutoff valve, instead old style idle jets. carbys are 32-34 pdsit. not sure if they have been modified at some stage but the central idle electromagnetic cutoff valve isn't wired nor the idle mixture enrichment valves. any suggestions ?

Phil74Camper Head in the Clouds

2,703 posts · joined Aug 2002 ·

#24342
Shouldn't matter too much Brian. A lot of old Kombi left-hand carbs have the Bypass Cutoff Valve removed and the hole blocked off. It normally sits at the top rear of the left carb (that is, in the upper part of the carb). Mine is blocked off with an araldited bolt.

Likewise, mine is an auto so it doesn't have electric idle cutoff valves either. The only wires my carbs have is one to the squarish idle mixture enrichment valve on the left carb, and the two electric chokes.

Just get the basic adjustments set as I've already described, then adjust the mixture and idle speed screws on the top left carb.

Steve Carter once wrote a detailed twin carb Kombi tuning article in the club mag - I will see if I can find it for you. It was a few years ago!

REDKG Officially Full-On Dubber

327 posts · joined Aug 2002 ·

#24407
i set the volume control screws at 2.5 turns out ( one was 1.5 other 3.5) and then adjusted central idle & mixture as you described. starts easier and seems(?) to run better.