Adjusting Dual Carbs. . . for rustybus and all

Hebster52 · Posted: Tue Feb 02, 2010 9:07 am Post subject:

I have one thing I was wondering. Do these instructions also apply if I decide to go with separete aircleaners for each side??
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cr@M · Posted: Tue Feb 02, 2010 9:12 am Post subject:

Considering the amount of vacuum lines hooked up to the air cleaner and the preheater it might run better with the original system in place. Assuming you have the original Solex's of course.
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Hebster52 · Posted: Tue Feb 02, 2010 9:54 am Post subject:

Was concidering to use them on an upright type-1 engine... Embarassed

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~Kris~
The Hebster52
The 912ST
The KidVRod project
The 356 Pre-A replica,SOLD
The 1966 Kommanderwagen, SOLD
The Doppel -67, SOLD
The Singlecab -72, SOLD

Amskeptic · Posted: Tue Feb 02, 2010 5:50 pm Post subject:

For factory dual carb bus people, this is the wiring I did in the Road Warrior to make tune up day a breeze. It also helps save your cut-offs from annoying failures of the spades or connections inside the solenoids.
Colin

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markd89 · Posted: Tue Feb 02, 2010 6:01 pm Post subject:

Colin, your stuff is great. I hope there's plans to compile it all into a book!!

Mark

stevehenderson · Samba Member Joined: January 01, 2008 Posts: 356

I need to fabricate this tubing I was given two sets of carbs without tubing any help?

vdubyah73 · Posted: Thu Feb 02, 2012 7:49 am Post subject:

make your own out of proper sized brake line.
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busdaddy · Posted: Thu Feb 02, 2012 8:09 am Post subject:

Here's the balance tube: http://www.thesamba.com/vw/classifieds/detail.php?id=1216059
Try Busted bus, The bus co or Avery's for the CIS tube (figure out exactly what setup you have first, there's a few different styles).
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Stuartzickefoose · Posted: Sat Aug 30, 2014 9:03 pm Post subject:

got a set of stock carbs for dads bus.,....time to see how long my paitience lasts! gotta get all the linkage, but the carbs i got were rebuilt and were free....so ill give it a shot before going all subaru on this one...
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tomfreo · Posted: Sun Aug 31, 2014 1:07 am Post subject:

The central idle cutoff solenoid on my bus has had its end clipped and pulling the wire makes no difference to the idle.

Would you tell me how I might do the "finger on / finger off" method to synchronize carb mix when I can't kill the central idle circuit by pulling the wire to the solenoid?

Also, I have no retard hose on my dizzie (205P). Should I just pull the vacuum advance hose and plug it? And when synchronizing carb mixtures, should I have the air horns on or off?

Thanks very much by the way for your great work. You're my first reference for these carbs!
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'77 Kombi 2L dual carbs
'61 Bug 6V 1600sp

busdaddy · Posted: Sun Aug 31, 2014 8:53 am Post subject:

You should be able to disable the CIS by screwing the large speed adjustment screw all the way in unless someone has overtorqued it in the past and damaged the seat at the bottom of the bore.
The hose should be off for setting the timing, it can stay on for synch as long as the diaphragm in the vacuum advance can holds a vacuum, if it's leaking it'll skew your tests.
You don't need to have the air horns on but you should have the connector tube and elbow for the CIS intake on when setting mixture.
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tomfreo · Posted: Wed Sep 03, 2014 6:51 am Post subject:

>>disable the CIS by screwing the large speed adjustment screw all the way in

I followed your advice and was able I think to get the initial mix OK but when it came to "fine tune" each carb mix by killing power to left/right carb cutoff solenoid the engine just died.

Is there anything I can do in this situation? With the CIS screwed in, the engine idles at about 600rpm.

Thx for help.
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'77 Kombi 2L dual carbs
'61 Bug 6V 1600sp

busdaddy · Posted: Wed Sep 03, 2014 7:48 am Post subject:

Temporarily turn each throttle stop screw 1/4 turn clockwise (equal amounts both carbs) and set it back after you get the fine tune done. If your timing and mixture screws are set correctly it should just barely idle on one carb in a shaky yet constant way.
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tomfreo · Posted: Sat Sep 13, 2014 7:43 pm Post subject:

>> Temporarily turn each throttle stop screw [...]

Ok, looks like I'll have some time to get back out to fiddle with the carbs again v. soon.

Just another question: Re setting the central idle speed/mix, Amskeptics aims for a final idle speed of 950-1000rpm.

I've a decal on the fan housing saying 875+/-75rpm. I'm wondering at which point in the instructions for setting the central idle speed/mix do I get the idle to 800-950rpm: should I adjust to that speed at the end of the tuning or should I have the idle speed lower from the very beginning?
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'77 Kombi 2L dual carbs
'61 Bug 6V 1600sp

airschooled · Posted: Sun Sep 14, 2014 12:44 am Post subject:

tomfreo · Posted: Fri Sep 19, 2014 8:20 pm Post subject:

>> original idle speeds were set for cleanest emissions
>> slightly higher idle speed (950-1000) is much nicer for oil pressure

I'll bear this is mind Smile

Fishing for comments but ...

"Pumping the brakes" fuel mix diagnostic suggests OK (no discernible change). Amskeptic's finger off/on diagnostic suggests fuel mix OK. However, plugs suggest lean mix (white-grey, no hint of brown).

Did carb tune procedure viz. Amskeptic - half way thru changed air filter, then started to fiddle with throttle set screw to stop engine quitting on fine-tune ... H'anywaay ... idle went real funky, maybe was the home-brew?, ended up setting initial mix screws 2 1/2 turns out and tuning idle mix and leaving the whole thing feeling a little disgusted with myself.

That was a week ago. This morning I ran down the road towards Paraburdoo (Pilbara region NW West Aust - wanta talk remote?) - 7kms at steady 85kph (52mph) and killed engine, cruised to stop, pulled plugs (#1/#3). Plugs suggest lean mix - pretty white, no brown.

Cracked open left/right mix screws 1/4 turn, headed back to Tom Price, 7k's. Again pulled plugs (just #1), no change in plug condition.

Now ... before I start getting excited about all this running up and down the road and pulling plugs, fiddling with mix screws ...

Is 7k's going to be enough to effect change on plugs for proper diagnostic? Would 1/4 turn open for mix screws be enough to effect change on plugs on plugs for proper diagnostic?

[Attached pic of local]

[/img]
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'77 Kombi 2L dual carbs
'61 Bug 6V 1600sp

busdaddy · Posted: Fri Sep 19, 2014 9:00 pm Post subject:

Playing with the idle screws will make no difference whatsoever with plug color after a high speed run, that's adjusted with float level/main jet size and air correction jet size. The pumping brakes and finger on/off test sounds like your idle is set fine, but unless you never touch the gas pedal and cruise all day at idle you'll have to determine if you need to go up a main jet size or go down an air jet size. To find that out you'll either have to get your hands on an AFR meter or do 2 runs, one at a lower RPM (40 MPH/60 KMH) and one at 60 MPH/100 KMH and see how the plugs look after each one.

If the gas on OZ is like the modern stuff here going up 5-10 numbers on the main jet usually does the trick, if it hesitates off idle increas the idle jet too.
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tomfreo · Posted: Fri Sep 19, 2014 11:05 pm Post subject:

Thing is, I'm playing with the mix screws on each carb, left and right. I believe this'll affect the colour of the plugs after a hi-speed run.

OK, brake pump diagnostic is only good for idle. With 'central idle circuit' disabled, however, finger on/off check is good for main jets?

If correct, is 7kms at about 85kph enough to run diagnostic on plugs?

Rolling Eyes

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'77 Kombi 2L dual carbs
'61 Bug 6V 1600sp

busdaddy · Posted: Sat Sep 20, 2014 8:09 am Post subject:

7 KM is pretty short, if the plugs were clean you may notice a rediculously rich mixture but if it's lean you won't see the tell tale deposits turning white yet.
The finger on/off does nothing to indicate main jet mixture and the idle screws have no effect on it either. The main jets don't come into play until the throttle is ~1/3 open and the RPM is ~2000+, you won't be able to maintain that in the driveway the engine has to be under load. You could remove the main jets completely and the engine would still idle, it would crap out when you got on the gas but it would idle fine.
Main jetting can not be adjusted externally, you must remove the jet and swap it with one of a different size, you can change main jets through the drain plug if you have eyes on the ends of your fingers but the air jet requires removing the top of the carb.
_________________
Rust NEVER sleeps and stock never goes out of style.

Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
Stop dead photo links! Post your photos to The Samba Gallery!

Слава Україні!

tomfreo · Posted: Sun Sep 21, 2014 8:46 pm Post subject:

So I gather tuning dual carbies is a matter of balancing air flow at idle and at speed, balancing and getting the correct *idle* mix between the carbs, and finally, setting the correct idle mix and speed of the so-called 3rd carb (on top of the left carb).

Although I think I understand that idle mix has an impact through to, what? about 2300rpm, it seems to be that fuel mix at speed can only be changed by swapping out the main jet. Is that right?

So, for arguments sake, if my plugs indicate a lean condition after a prolonged run at about 85kph/53mph (and given no vacuum leaks) the only fix for that is to change the main jet itself? Fiddling with the left/right mix screws won't affect the mix at speed, right?

Just one more thing: how do the throttle set screws feature in all this?

I appreciate your advice, Busdaddy ... I can follow instructions but feel a little stupid when it comes to carbs. Embarassed

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'77 Kombi 2L dual carbs
'61 Bug 6V 1600sp


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