Auto trans has different carby?

[nbturbo]

I have stripped both carby's from an auto trans equipped Type 3 and found them to have a small valve on the throttle butterfly plate-which is not on the manual trans carby's.From the gasket kit,it's called a "valve-hot idle" It has a port which is below the butterfly.It has a brass plunger which has a spring plate(which is adjustable for tension) holding it-but it is loose.Has anybody seen these carbs? I can't find any info from a Type3 or late Bay workshop manual.

[Marvel]

I've got these on mine although it's a manual. Maybe the engine or gearbox was changed at some time.

[nbturbo]

I found a pic of them in a Bus Manual-but no reference anywhere in the carby section as to what they are or adjustment procedure.

[Bobnotch]

Nope, never seen that before. But then all USA models with AT came with FI.
_________________
Bob 65 Notch S with Sunroof
71 Notch ...aka Krunchy; build pics here;
http://www.thesamba.com/vw/forum/viewtopic.php?t=249390 -been busy working
64 T-34 Ghia...aka Wolfie, under construction... http://www.thesamba.com/vw/forum/viewtopic.php?t=412120

[rustyfastback]

I have a set of carbs that have altitude compensators. They have this small valve at the base also. They are later versions with the diaphragm style choke pull off instead of the piston type pull off. No idea it they are off an automatic engine as I bought them at the swap meet.

[KTPhil]

[Donnie strickland]

If it's on the throttle butterfly, I wouldn't think it has anything to do with altitude. The mention of "Valve - hot idle" implies that it's there to help an automatic car maintain its idle speed a little better.

VW used a device to do that on the automatic transmission 1971 and on Type 4 cars, which used a vacuum-operated piston like so:

But that's different than the mechanism nbturbo posted. As Bob says, we never saw automatic transmission carbureted Type 3's here in the States.
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71 Elm Green FI A/T Squareback

[rustyfastback]

Here is the set of carbs with the altitude compensator jets. These were used in higher elevations. I was mistaken as the have the piston choke pull off not the later diaphragm type that is held on with 3 screws. I have maybe 40 sets of factory dual carbs & this is the only set I have with the altitude compensator jets. Check the pics

[nbturbo]

WOW- that's something I have never seen before.I am assuming that the big alloy thing that's taken the place of the threaded plug to remove main jet,releases more fuel into the bowl at less dense altitude pressure to increase the fuel level in the bowl.I will never know if this engine has both original carbs,but 1 has the diaphragm choke pull off and the other has the piston type.I see both those have a brass fitting above the idle mixture screw,which has a check ball in it.We had the 12v solenoid here in that same hole, which from memory was to shut fuel from the idle circuit to prevent any run on after the ignition was turned off.Thanks for all the info and pics.I have also discovered that rod coming from the back of the choke housing is to adjust the fast idle while on choke.

[KTPhil]

No, it modified the jet itself-- the gas flowing FROM the bowl, not TO it. It's a lot of mass to hang on a fine thread in soft metal!

I'm still wondering what that damn hot idle gizmo does... what's underneath it? Does it bleed a little more vacuum advance by allowing more suction into that port? Or maybe it affects the mixture in some other way by bleeding air in? I assume that's a bimetallic spring on it?

[HenrikL]

The parts book says that option M249 (automatic transmission) have different carbs.

[Bobnotch]

[reay]

Yep -Those are what my 68 T34 Automatic came with. I wanted to put in larger main jets, and the altitude compensators have they jets built into them, so I went to standard carbs. (Among other reasons). It's also kind of hard to find floats for those. They aren't the same as a regular type 3 carb - I think 71 bus floats work.

They are actually pretty cool carbs. If they work for you, I'd definitely keep them. I'd love to see how the Altitude Compensators work. I basically live at sea level, so I never had a chance to test them.
_________________
Tom Reay

Da weiss man, was man hat!

68 Karmann Ghia Sunroof / auto T345
66 Standard Microbus T221
66 1200a Standard 115 with factory ragtop

[Multi69s]

[KTPhil]

Another thread on the subject...

https://www.thesamba.com/vw/forum/viewtopic.php?t=412120
And an image referenced there:

And from here...
https://www.thesamba.com/vw/forum/viewtopic.php?t=173175

...it is said:
"The factory provided an cold enrichment device to the central idling circuit when cold and it also attached a "hot-engine idle valve" to the throttle bodies on auto-trans buses that provides additional idle air to the dual carbs when extra hot. These are both simple bimetals that have a little brass plug that "un-plugs" when needed. They only need to be clean to work. The cold enrichment device has a resistance heater with a wire attached to the box. The hot idle compensator is purely mechanical."

It still doesn't specify exactly how it works, other than "additional idle air bleed". I'm not familiar with the innards of any but the old 28 and 30 PCI and PICT carbs, so the later carbs with multiple idle adjustments work differently... I presume this device bleeds air into the more-complex idle air circuit on those later carbs.

My '71 FI automatic sometimes idled a bit low when hot and in Drive. Of course, being FI, it lacked this gizmo, but did have some temperature compensation built-in. I just shifted into N when it got bad.

I think this device was an early attempt at dealing with low/hot/Drive idle. Newer solutions involved a solenoid on the idle screw when in Drive, but I am speculating the compact Solex design along with the tight manifold spaces made that hard to implement, so they took the expedient of bumping idle speed when really hot with this gizmo. If someone could figure out just what passage this bleeds into, that would confirm it.

Also, these are listed in the instructions above as Bus carbs... were they ever stock on Type 3s?

[Multi69s]

KT,

With the second thread link, you just revived some nightmares for me. When I first put the T4 engine in my Square, I tried to use the stock carburation. I even used that thread for trying to tune them. I guess that carb setup is like the Type 3 FI. When everything is right it works great. However, I found them to be the most convoluted pain in the butt to work with. The changing idle and off idle response drove me nuts, and I have never been more glad to get rid of them. I would much rather fix a PO hacked FI, then ever touch those things again, and I am a carb man.
_________________
69 road Bug 2110
73 Squareback - 2L, T4, Automatic W/ AC
Gone, but many fond memories 69 Baja Bug 2010 - 5 Rib Bus Transaxle
Gone but not forgotten 72 Baja Bug 2010
My builds
T4 into Squareback http://www.thesamba.com/vw/forum/viewtopic.php?t=458944&highlight=
Auto Trans Rebuild http://www.thesamba.com/vw/forum/viewtopic.php?t=516066&highlight=
AC in Squareback https://www.thesamba.com/vw/forum/viewtopic.php?t=...highlight=

[reay]

That may be why I went away from them as well. I couldn't get any response of of the air /fuel mixture adjustment needle. I think the air was leaking in the hot air valve.
_________________
Tom Reay

Da weiss man, was man hat!

68 Karmann Ghia Sunroof / auto T345
66 Standard Microbus T221
66 1200a Standard 115 with factory ragtop

[nbturbo]

Yes- thinking that it would be easier to just thread the hole and screw a bolt in there.Reckon that the small brass plunger would never offer a total seal anyhow.Fitting the auto and engine into a 63 Bus.Have nearly finished converting the engine to upright,after a new set of barrels and overhauling the heads.Got a lot of work on converting the Bus to IRS.

[Variant]

[reay]

/\ /\ That total makes sense! Thanks for the explanation!
_________________
Tom Reay

Da weiss man, was man hat!

68 Karmann Ghia Sunroof / auto T345
66 Standard Microbus T221
66 1200a Standard 115 with factory ragtop