'61 348 3x2BC Vacuum Secondaries Tank
- Thread starter ThumperNZ
- Start date
ThumperNZ
Well Known Member
We used the ShowCars Part #3219B, had to modify it to fit, the tee clashes with the back carburetor. The check valve looked restrictive, but tested ok. Fitted it, no secondaries. Removed it and there is no check valve function. So I've reverted to the AC type check valve we tested with on the dyno. IMHO the ShowCars part is junk, not worth trying. if your brass check valve works, go with it.
Grape
Active Member
The Show Cars check valve is pictured on their site with the arrow going the wrong way on the check valve. It should be pointing toward the front of the car, not away from the back of the carb. I'm not sure how they shipped it but the image is definitely wrong and will never make vacuum as shown.
The brass check valve costs around $8 plus a couple fittings from Ace hardware. I have it going out of the wrong side for now because this looked better with the T fitting that I used. I have the repro stainless T fitting on the way and hope to find the correct check valve in the future.
The brass check valve costs around $8 plus a couple fittings from Ace hardware. I have it going out of the wrong side for now because this looked better with the T fitting that I used. I have the repro stainless T fitting on the way and hope to find the correct check valve in the future.
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ThumperNZ
Well Known Member
Regardless of how they shipped the assembly, it wont fit anyway, so I made sure it was flowed correctly after I had modified the Tee so it would fit (it needed about 3/16" taken off the check valve side, and retap 1/4 NPT). The check valve contains a plastic check and looks to be poorly made. I does not seal at all now.
Are one of these the correct check valve ? Brian is selling them.
http://www.348-409.com/forum/threads/check-valves.35314/
Paul
http://www.348-409.com/forum/threads/check-valves.35314/
Paul
Grape
Active Member
I believe those are for an automatic transmission with the extra vacuum port before the check valve. I will check to see how much he needs for 1. Thanks for the heads up.
Lt.FrankDrebin
Well Known Member
Or that extra port is for vacuum-operated wipers? The check valve I have is like the one(s) pictured, but shorten it a bit to take out the extra port. There was one on EBay for about $60 recently. Let me see if I can find it.
Grape
Active Member
I am still fussing with my vacuum secondaries. After killing the engine they will only hold open for a couple seconds when I hold the throttle wide open. The vacuum can be heard disappearing quickly. The secondaries will stay open a little longer when driving it but also runs out of vacuum fairly quickly. I think with the vacuum tank and check valve, the system should stay open for quite a while even with the engine off? How did you remedy yours letting off after a second or 2?
The check valve will hold vacuum as long as you are not calling for it and when you do it will not build up unless you have the throttle closed.
So when you run out of vacuum in your tank you will not have any outside carbs.
I know as much as you would like for this system to work....I don't think you will be happy tell you go to some mechanical linkage.
So when you run out of vacuum in your tank you will not have any outside carbs.
I know as much as you would like for this system to work....I don't think you will be happy tell you go to some mechanical linkage.
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Grape
Active Member
The system is too cool and quirky for me to give up. I may try an air tank inside the car as a vacuum source to see how long that will hold the secondaries open.
A vacuum gauge will tell you what is going on.
For racing purpose I run my 2 X 4 1 to 1 no progressive linkage.
The deal with the vacuum control sec is they need to be controlled by the signal at the base of the outside carbs......so this signal has to be on spot if you know what I mean.
If this system is controlled by a reservoir you would need a real good vacuum switch to make this work well.
You can still drive a progressive on the street with great success and a lot of fun......could be better on the track also
If this system is controlled by a reservoir you would need a real good vacuum switch to make this work well.
You can still drive a progressive on the street with great success and a lot of fun......could be better on the track also
as an interesting point back in the day in 1961 and early 62 a guy around here had a late build 348 FH 4 speed and 4:10 Impala coupe. His big claim to fame was that he always ran vacuum activated carbs and was almost unbeatable. Wasn't until the 62 409/409's came out that he started losing any with regularity. I looked at the motor that actually came out of his car several years ago as many around here thought he had switched to a 409 but it was a stock FH with vacuum linkage.
Robert
Robert
Grape
Active Member
The tank holds vacuum for a long time when the engine is shut off so the check valve is working. It is leaking down quickly from somewhere at wide open throttle, either through the slide valve or the pod at the front. It seems like the system should hold the carbs wide open until you let off the gas and allow the slide valve to return to the top.
There is a hose running from the slide valve to the top of the front carb. I'm not sure what this one does. The other hose from the slide valve activates the pod at the front. I will get a vacuum gauge on there to see what is happening.
There is a hose running from the slide valve to the top of the front carb. I'm not sure what this one does. The other hose from the slide valve activates the pod at the front. I will get a vacuum gauge on there to see what is happening.
Grape
Active Member
These carbs were NOS, new in the original boxes and mounted about 3 years ago. Maybe a diaphragm is dried out or does have a hole or crack after 50 some years in storage. Thursday morning I will check with a vacuum gauge and hopefully find out where the system is bleeding off.
