Vacuum secondary actuation, vacuum passage

[gr_diver]

Hello dear friends,

I've been messing with my carb lately, because although I' ve rebuilt it something does not feel right when driving the car. The engine lacks power below 2500rpms, and does not willingly rev above 4000rpms. If I "force" it above 4000rpms, it starts misfiring somewhere around 5000rpm. Between 2500-4000rpms (main jet effective range) everything feels ok. Trying to solve the upper power band, I was checking the vacuum secondary actuation in the FSM and my Haynes manual. They both describe the same vacuum passage, as seen in the picture I attached.

I tried to see if it is blocked. I disconnected the vacuum case from the air-horn, and spayed WD-40 in the passage, to see if/where it would come out from. Fluid came out, but to my surprise, instead of coming out only from the wall of the primary venturi, it came out from the secondary venturi as well. I did the same to my old parts-carb, that had exactly the same issues (and that's why I replaced it) and the same thing happened.

Since both carbs do the same, it would be an easy guess to say that it is normal. But when thinking about it, it might be NOT. Having an open end in the actuation passage (the one that exits in the secondary barrel) would yield NO or very little vacuum in the actuation system, something that would keep the secondary closed (top end lack of power). Additionaly, since these ports exit in the barrels just below the minor venturies, when driving on the primary barrel only, it might be like having a vacuum leak, since pure air and not ready mixture is sucked below the minor venturi from the inactive secondary barrel, thus dissolving the mixture (does the lack of power below 2500rpm get explained here?).

Give me your thoughts on the matter, does my thought sound correct? I am thinking that maybe during manufacturing of the carbs, the port in the secondary was sealed before insertion of the venturi with something that due to age gets dissolved and the passage opens causing these problems.

P.S. With the stock carb/ stock jetting, admittedly my engine runs on the lean side. Could that be another outcome of the condition described above?

Thank you

Antonis

[opelnut10]

Sounds like you are a prime canidate for a Weber 32/36 sawp. If you are not up for that, find a GT Solex (from someone that has gone to Weber) change out the bottom base section (which has mechanical secondary) and eliminate your problem for good.

[gr_diver]

I need confirmation whether this might be a logical thought, since some RTV on the fingertip would be enough to seal the passage again... Re-sealing the passage is a very easy task, since access to the port's end only involves removal of the minor venturi in the secondary barrel (which is held in place by a single screw on the outside of the carb's body).

[nobody]

Seems there was a moderator that used to fix those vacuum diaphrams over in England. I'll let Baz take it from there. I can't laugh and type at the same time. Something about birth control for a solex.

[gr_diver]

That was about repair of punctured diaphragms, not about internal carburetor passages.

[baz]

yep best use of a condom i ever found and btw im not a mod any more

gtg if you undo the 3 screws that hold the cover on and take the cover off to get at the diaphram, the rubber has usually split , take 1 condom and cut out a new ring to go over the top then use superglue/ crazyglue to stick it on the top so it is fixed to the centre with an overhang outside the cover , replace the cover and let the cover nip the overhang this will fix the leak

no leak no leaning out of the carb

[gr_diver]

The diaphragm itself is in good condition. I think that a passage that used to be sealed might have opened.

And my post was to see if carb gurus here can confirm that my thought/explanation MIGHT be correct.

thanks

[nobody]

The passages seldom failed but the diaphram was notorious for failure.

[baz]

i am only going from memory as i have not used a solex since 1983 but i think they are both open and only the diaphragm seals it

i must see if i still have my old door stop sorry solex lying around some place i know i have a weber or two (down draft and side draft) but cant remember seeing the door stop in a while

[gr_diver]

I am thinking that the second open port might be a problem, because I remember when I first tried to fit a vacuum gauge to the car, I used a "T" for it on the small PVC hose. Because the hose's end was open in the valve cover, the vacuum gauge showed no vacuum. And I think that something similar happens inside the carburetor, due to the open end in the secondary barrel.

[gr_diver]

I was a little anxious to see if plugging the passage would make any kind of change, so I took the car for a test drive. At first I drove with the passage open (as it was so far), then pulled over and from within the barrel I sealed it with a small piece of chimney sealing alu-tape (heat and fuel resistant).

The difference was tiny if non existent, so I removed it again and called it a day...

Thank you for your replies, and I am sorry if this was a "stupid" thread. Maybe I am going a little crazy trying to figure out what's wrong... In fact nothing is seriously wrong, but I think the car can/should run better.

Regards

Antonis