I've replaced everything in my brake system. Today I got another proportioning valve in the mail, and it was a waste of money. I thought my valve was for drum rears, but I was wrong. I thoroughly bench bled the master, and then gravity bled the rest.
I've replaced the power booster/and master twice, because I thought the booster was leaking vacuum. I have no idea why it stalls when I brake hard. I thought it was a carburetor problem. I posted in the carb section but that wasn't much help. I think i'm going to buy a phoenix injection pump at this point.
I also have a vacuum canister. I forgot to mention my rear calipers are cast iron, and they are working properly. I know of the problem with them. It doesn't seem like there's too much pedal travel, but I don't know what's normal on these vehicles.

 

have you checked over all of the vacuum lines i think that could be the culprit

 

This would happen on earlier 3rd gens with stock qjets, I'm not sure about later ones:

There's a big rubber vent line connected to the top of the carb that part of the emissions system. It's suppose to route evaporated vapors to the charcoal storage cartridge when the engine is off. When the engine is "on", a vacuum powered check valve closes the carb vent and allows stored vapor to be sucked out of storage cartridge and into the engine to be burned

What might be happening is the check valve has started to go bad and vacuum is being supplied to the carb vent while the engine is running. When you stop hard, gas sloshes to the front of the carb bowl and a big slug is being sucked down the vent line and into the engine causing it to stall.

Disconnect the carb vent line and see if it is full of gasoline. Another way is to disconnect and plug the vent line and see if the problem goes away.

 

I found your thread in the carb forum and you have a 700DP.

The first thing you need to do is figure out if it is a carb or brake problem. Block the vacuum line for the brakes and see if the problem goes away.

Most likely it's a vacuum issue with the carb installation.

 

I'm pretty sure if I block the vacuum line it wont happen, because I wont be robbing all the vacuum when braking. I don't have a vacuum pump, but I know for sure one of the reman'd booster I got was leaking vacuum. I don't know what else to do at this point. I'm guessing there might be some air in the master, and the pedal travel is too excessive? I have no idea at this point. thanks

 

I doubt it's air in the master because you wouldn't be able to brake hard at all and you'll feel it right away.

Does the engine stall out by just suddenly pressing hard on the brakes when you are parked at idle? As it's not a stock engine setup, you might need a vacuum restrictor on the connection to the intake manifold. (The reservoir goes on the booster side of the restrictor and takes care of vacuum supply to the booster). Try taking a pair of vice grips and slowly choking down the vacuum hose to the intake manifold to get an idea how much restriction is needed.

I still think it's what irocz said. There must be a disconnected vacuum line that you missed somewhere that needs to be plugged.

BTW, on a CC qjet, the computer momentarily kicks out the A/C idle solenoid for 1-2 seconds when you suddenly get off the gas. Try increasing your idle a couple hundred RPM to see if it clears up the problem.

 

The engine doesn't stall when I slam on the brakes sitting there idling. Just when I push the clutch in and i'm moving, I slam the brakes, and the idle gets low then stalls. I had the same problem with my Vacuum secondary 600, but not as bad.
I also forgot to mention I have the vacuum line hooked up to a knockout on a spacer. I know for sure there isn't a vacuum line disconnected. There are only a few vacuum lines on my setup. I'm thinking it might be my carb, this thing has been an eBay nightmare.
If I knew more about carbs, I would've probably solved it. I did learn a lot rebuilding the carb that was supposably rebuilt, but I still need to learn.
I thought that the vacuum canister would solve my problem, but it was a waste of money along with the prop valve.
I did try running around with the car idling at 1k, but it didn't solve it either.

 

Lower the rear float leve on the holley.

It sounds to me that fuel is sloshing forward under braking and going down the intake.

I bet it goes away when you do this.

I do not believe that it is vacum related. It only occurs when the car is being stopped and weight is being transfered forward. (fuel is weight)

 

how much gas is in your tank?
My 86 Trans Am with a 1406 carb used to stall when braking pretty hard when I had less than 1/2 tank in the car.

 

ditto on the float level issue - you could try putting a taller vent on the back one too... i have this same issue if i hit the brakes hard while in motion.

 

Thanks for all the responses. I thought I was supposed to keep the float levels just so they dribble out on both. I will lower the level on the rear, and report back, but right now I have bigger problems.
The problem doesn't change in relation to the ammount of fuel in my tank that i've noticed. I can't believe it was so simple, if I knew more about carburetion I would've figured it out by myself.

 

Well i've lowered the rear float level more than 1/2 turn, but it still does it. I guess I can lower it some more.

 

Mine does it when I come into the stop box at an autocross.

The motor has a 650 Demon and the bowls have whistles in them.

I figure it still must be dumping fuel though because it caught fire once after it stalled.

 

I have the same issue, but nothing is stock.

I bet it is fuel going up the vent on mine. I am going to put a hose on top with a cut in it and have it go to the other bowl, and see how that works. I will report back to here if I solve my problem.

Mine never stalls, just drops WAY down and comes back. I went HARD from 85 to about 30 and it did it, but still didn't stall.

Oh and I have a vac canister too, and I have to idle around 1K to 900 all day long. It is a crazy motor, but a DD none the less.

Hope to help. Later

-Dennis

 

I lowered the float some more and now it doesn't stall, but it comes close. Thanks for the advice, I appreciate it.
After all the trouble i've had with the carb, i'm about to switch back to vacuum secondaries, it's tempting. Fuel mileage was quite a bit better, but the engine loves the carb.
Someone also told me I shouldn't have jumped from a vacuum secondary 600 to a 700 double pumper. I also changed the intake to a Dart Kool can, and it screams now.
I've never heard the term whistles on a carb.

 

When you take a float off you will see them. They are white plastic things that kinda look like a whistle.