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Tue Dec 09, 2025 11:04 pm

Ive got a 1500 sp motor and all carbs and conditions could not get it to run right. Mostly due to constant carb issues with each next one being the next new problem and not much experience with a proper working carb to begin with. I found a h30/31 carb on ebay with the description of being brand new and installed by vw mechanic and no issues and 30 miles into the use of this carb the car was involved in a front end collision and removed the carb befor the car was towed away to be junked. So im thinking im getting a real life new and good running carb that is free of any need of any rebuilding or tinkering."PLUG AND PLAY" so to the point. Look at the picture i provided and you'll see how the throttle arm that is involved with deceleration ( a CA 70's emmisions trick) is pulled out past the arm that also is ths top hook for the throttle spring. So ive never seen them NOT INSIDE that arm and looks very intentional in the way it is. I know or heard they are not used or removed and irrelevelent tgess days but in haste i fit it back the way i thot it should be. But it is shown tgat way in the pic which is tye way it was on a fine running bug before he removed it. Im a little confused becuz it does affect the throttle return in that it does not return as far as im used to. Where does evsryone run this second arm that im told is irrelevent these days?

Wed Dec 10, 2025 5:09 am

I think a larger photo of your engine showing distributor and vacuum connections would help others here see potential problems. If it is a single port engine, I do not think you would need the adapter below the carb, I am confused on that. The previous owner of that carb could also have had a different distributor and vacuum line set up which would produce different running results on your car. Post a couple more pictures if you can for more ideas and info.

Wed Dec 10, 2025 8:27 am

This is a photo of my own Brazilan Solex 30/31 PICT on my own VW, which is a 1600cc dual port so my carburetor does sit on an adapter.

This carburetor is about 2 decades old, and I rebuilt it in 2016 when I resurrected my VW.

Mon Dec 15, 2025 1:34 pm

IMHO your linkage is assembled incorrectly. Here is a close up pic I found in the gallery.

It comes from this thread which had a very good write up as well as a video that shows how that emission diaphragm works.
https://www.thesamba.com/vw/forum/viewtopic.php?p=7873691

In the above pic you can see that when the diaphragm linkage pulls rearward on the secondary linkage arm it holds the throttle arm back (note the throttle arm screw is not touching the fast idle cam at all) so the idle remains up. The screw that passes thru the spring perch controls how far rearward the diaphram is allowed to open the throttle as it delays the full close of the throttle plate. So the screw controls the engine rpms while the diaphragm is ON.
The flat of the secondary arm rests on the tip of the screw. Since your flat is on the outside of the spring perch I don't know how the adjustment screw would work.

As far as what the secondary arm does when there is no diaphragm... with nothing to pull the arm rearward it does nothing as long as it is not impeding the primary throttle arm movement. You should be able to adjust the screw thru the spring perch all the way in until it contacts the flat at the tip of the secondary arm, pinning it in place. This would completely prevent the secondary arm from moving, but since there is no diaphragm pulling on the arm it doesn't matter.

Tue Dec 16, 2025 11:57 am

So with out that valve its not doing anything correct?

Tue Dec 16, 2025 1:10 pm

billygoattorture wrote: So with out that valve its not doing anything correct?
I don't know? Typically, I'd agree. But your linkage arrangement is not typical. :shock:

Post a few more pics of you linkage. Your pic above is partially blocked by the hose. A different angle would also help
In the normal linkage arrangement the flat part of that secondary arm could not move any further rearward than the spring perch (eg. adjustment screw removed). Your arm is already further rearward than that since the flat is on the other side of the perch!

How difficult would it be to remove the connections to the linkage, remove the nut holding the linkage to the shaft and reassemble all the linkage parts per the assembly diagram? It looks like you could do it with the carb still mounted to the intake but I would suggest removing the carb and working on it at a bench/table.

Tue Dec 16, 2025 7:30 pm

the carb was not assembled correctly after someone took the top off.
to fix it, you will need to take the top off yourself, move the arm back to its proper position behind the casting and put the top back on. the secondary arm will require no further attention or adjustment.