blctalon

I've been working slowly at getting the vent controls to function correctly. I have a semi low vacuum at the black hose that goes into the firewall grommet. At the back of the a/c control face plate I still have that signal of vacuum. My problem is I can only get it to switch from floor to defroster. It will not go to the a/c vents at all. It just stays at whatever setting it was at before, be it floor or defrost.

I don't believe there to be a leak in the system, just a problem of low vacuum (haven't measured yet, how much required to make this work?) but I do have a barry grant might demon carb. The main vacuum port on this carb is T'ed to a pcv and brake booster. If I hook anything else up I loose some brake functionability.

The other 2 small vacuum ports on the carb go to vac advance for my msd e-curve distributor, the other is constant small vac port that I have the lights and a/c vacuum hose hooked to via the stock 2 to 1 vac fitting behind the carb. My lights do come up on this but it's slow and uneven. I'm thinking this little port on my carb isn't enough vac to make everything work. Any thoughts on what I should do? I really want to get this figured out so I can put my dash and console back together and install my new carpet.

SH-60B

If you have a Mighty Demon carb, you probably have a cam and heads to take advantage of it, right? Are you making suficient vacuum with that cam to even run vacuum accessories?

blctalon

230/230 cam and afr heads. I've had the engine in the car for a while but i'm tired of cooking my head and face in the summer time with no a/c so i'm trying to get the controls sorted out and reinstall the ac.

As far as vacuum goes, I think it makes enough vacuum for stuff to work, I'm just afraid I'm out of large enough vacuum ports to hook my headlights/ac vacuum stuff to so I hooked it to the small port on the carb and it seems to kind of work. I guess my main question is, is it possible to have just a minimal amount of vacuum present at the temperature control panel to only have the bi level door work half-assedly?

The Money Pit

If your headlights pop, I'd figure you have enough vacuum to pull in the AC vacuum servos. I'd look at the vacuum control valve under the dash. I have the same issue, and have a valve on order. If you squeeze the valve in between your fingers, maybe the seal would work well enough to determine the valve is the problem.

My cam pulls about 8" vacuum at idle, and in testing I was able to get my vents to work by squeezing the valve.

pauldana

I am pulling 11" and have the same problem. Are you talking about the center console switch (VALVE??) for the A/C stuff? hope not, mine is new and still have the problem...

blctalon

Is your 8" right off the carb or somewhere else? I'm wondering how much is adequate to get the actual controls to function properly. I have vacuum at the firewall 3 way grommet. I can pull the black line out and put it in my mouth to feel it suck, but it doesn't suck really hard.

Also, the valve thing I think you're talking about is the rubber vacuum piece that holds all the lines and goes to the back of the temp controls switch on the console right? I tried fiddling with that and nothing really changed. I do have a brand new temp control unit that came with a new switch this rubber thing plugs into. If you're talking about the piece of duct work with the valve that moves the door to the vents, I've tested that for leaks and it's good. I had the dash apart and was able to suck that closed with my mouth and hold it.

As far as my headlights popping up, the left one comes up slow and at the same time I can see my right one trying to rise, but will fall and maintain about an inch open. Once the left one opens all the way then the right one pops up. Like it just barely has enough vacuum to pop them open.

The Money Pit

That's the valve I was talking about. I took mine apart once and smeared vasoline on the rubber seals inside, and it made a huge difference, but the "fix" didn't last.

The 8" vacuum was taken right off the carb, .....pretty lumpy cam I know.

My headlights quit years ago, and I've been too cheap to fix them. I just push them up when I need them up. Mostly drive during the summer during daylight anyway. With my cam it would take a few minutes for the headlight to open, as you say one,.....then the other. I had a scare one night though that convinced me to just do away with the vacuum control. I was coming home at dusk, and hit my favorite spot. I nailed it, the speedo tipped 125 mph or so, and the headlights dropped shut.....................

Now I push them up, and tyerap the stops so they stay up during the fall. In the spring, I cut the ties, and push them down.

Back to your problem.....When you rev the engine, does the vent system work. You should have much better vacuum when the engine rpms go up. (Not WOT, just off idle)

blctalon

No, it doesn't seem to change the vent issue if I rev it. I tried that a couple of nights ago just to see what happens and it didn't go to the vent, but would still go to the floor and defrost.

justanotherdoe

Do you have somewhere to put a fitting in the manifold and get your vacuum for lights and interior controls from there?

I had the same problem trying to get the vacuum activated stuff to work on a demon carb with only the one large and 2 small ports. Too many Ts, and nothing worked well. A manifold fitting gave me two more vacuum source points.

I eventually put in a stock qjet to improve fuel economy, but still use the manifold fitting for lights and interior controls.

blctalon

As luck would have it, the only place to put a manifold fitting is being blocked by the big fat demon carb. This is on an Edelbrock RPM Air Gap manifold. I saw somewhere on here someone suggested drilling and tapping into the manifold to put another fitting but I don't care to do that.

The other option is putting a small spacer under the carb to get enough space to make a really flat special T fitting work. This again isn't an option because it's sitting high enough as is and hood clearance will become an issue. I have the TV cable system from bowtie and it uses a thin plate under the carb so adding another plate/spacer doesn't sound like a hot idea to me. I might have to settle for one of these options though.

Ganey

Main vacuum port to brake booster & to most everything.

PCV (& if Fuel Tank Evap.) to separate port "constant small vac port".

The Money Pit

Well,....new valve didn't fix the problem. I must have been thinking of when I was running the 355, which had quite a bit smaller of a cam...

I measured 8" vacuum right off the control valve, which is exactly what I see off the carb, so no loss there.

Is there any possibility of recalibrating the vacuum servos,.....stretch a spring, move a lever,..... Or maybe intall a vacuum pump of sorts just to work the power brakes and vacuum accessories?

justanotherdoe

My bubba approach was to cut an inch and a half length of a smaller od/id hose and slip it inside the pcv hose (tight fit) to meter the vacuum to the pcv valve. This was enough to boost the vacuum signal to operate the headlights but still maintain an operating pcv when the lights weren't opening/closing. The lights were still slow to move, but without the pcv hose id restriction, they wouldn't move at all.

It was cheap, easy to install, and in my case, it worked.

The Money Pit

Funny you mention Bubba,....I already did the restriction you mentioned a while back when I was trying to resolve an idle problem.

My lumpy cam took me a year of tweaking to finally get it to idle in gear. Ended up with 36 degrees locked out timing, major carb recal in the idle circuit, and now it'll idle at 900-1000 rpms in gear.

I guess I need to buy a hand vacuum pump, and test to see if that'll even work before I worry about figuring out how to make the perminent fix. At this point I have some defrost/vent, but I may as well be waving my hands trying to make a breeze for all the flow I'm seeing out of the vents now.

Ganey

Mark
Yes you can push them up. The headlights should lock up in the up
position. Sounds like an adjustment is needed.



Try rerouting the vac. hoses similar as I mentioned above. Vent vac. could go to a small constant port if no PCV to it.

The Money Pit

I'm using the full vacuum port right off the base of the carb, direct to the vacuum control valve under the dash. There are no T-s or any other connections, as most of the "stuff" has long since been removed. I don't even run a vacuum advance on my distributer at the moment, and the tranny is a full manual VB.

Ganey

The vents can be locked open, heater locked closed, vac. motor springs removed or vac. motor removed ...