Engine stalls upon braking

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4spdcuda66

4spdcuda66

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Poly 318 with Carter BBD 2bbl in a '67 Fury. Car was running smoothly until a week ago. Ran fine at part throttle and cruise, but would idle really rough at a stop light. Took the carb apart, found some sediment in the fuel bowl, so I cleaned everything with carb cleaner and blew everything out with compressed air and put it back together with a new carb tune up kit. Now it idles fine, but even after light acceleration, it stalls. I can't drive it thirty feet and hit the brakes without stalling. Runs fine at idle in Park and in gear, seems to be ok if I let it accelerate on its own without hitting the gas, but will stall if I hit the gas pedal and then stop. Car has manual brakes, all vacuum hoses are good, float is adjusted properly. What am I missing?
 
Sounds like fuel bowl level problem. Are you sure the floats are adjusted properly? I'd double check them.

Also is it automatic? Does it stall cause of the braking? Or the 2-1 downshift? I doubt it's that, but that can be a problem. Can't be low vacuum with manual brakes. So those are the first two that come to mind.
 
Sounds like the float level is too high and it is spilling fuel into the venturis when stopping.
 
Easiest way to check downshift is drive it in just first. And then do the same tests. If it doesn't stall. Something with the downshift is loading up the engine and stalling it.
 
Float adjustment is spot on. Accelerator pump is set right and squirting as it should. I can let it take off on its own, get up to 15 mph or so and hit the brakes with no stalling in forward or reverse. If I hit the gas to take off and then hit the brake it stalls forward or reverse. The two metering screws at the base of the carb are backed out 1-1/2 turns from seated. I don't have a clue as to what's going on with it.
 
I have been building carburetors since the late 70s and I have never seen a carburetor that had a float level that was set in stone. All of the kits I have ever seen had several different float level settings for different applications, even with the same carburetor. Are you 100% sure you are using the right setting?
 
No booster. Manual brakes. Rusty, I tried a few different settings. Before I posted this thread, I thought the float was too low and starving for fuel. I readjusted it slightly higher, got the same result, then posted this thread. As per your suggestion, I took the carb off the engine, checked and re-set to the specs in the instructions. I get where you're coming from though. The float is about dead parallel to the body. The venturis are on the opposite side of the wall from the fuel bowl, so the gas can not splash into them. If that were the case, it would stall from a coast as well as from acceleration. I'm going to take it apart and inspect everything again. I have to be missing something.
 
Did the float have a baffle you omitted? Lots of them do.
 
Do you have to crank-n-crank with the throttle open to restart? That's flooding.
If you have to give it a few pumps to help start, that's starving for fuel.

If the gap at the points is too small, you won't be opening the points to make spark when you take your foot off the gas and the
vacuum canister goes full advance.
Try opening the point gap a smidgen.
 
I'm thinking that carb has the vacuum port under the throttle plates and pulls a high vacuum to the advance canister when the throttle closes. Dwell changes wirh vacuum advance, and if the points aren't opening, engine dies, more likely when engine is warm. There is also a very particular weird sickly sweet smell when starting a hot engine where the points aren't opening.
I was once at a Circle K in Phoenix in a stupid new rental car, and a beautiful red '64 Galaxie XL was parked next to me.
They came out, it wouldn't start, and I thought, Ooo-ooo that smell, can'cha smell that smell?
I opened up their points a little and they drove off happy.
 
There was no float baffle in the carb. Points have been replaced with a Pertronix set up. It's not flooding. Starts right up when I bump the key.
 
Advance plate in dist still changes gap to reluctor and sensor. Check the gap.
Too large or too small, and you will lose spark when advance plate shifts with high vacuum when throttle snaps shut.
 
It has been a while since I've had time to mess with this thing. Since it was down, I pulled the covers and set the valve lash for the first time in ten years. Not terrible, but they were due. It looks like the float level was not as "spot on" as I had thought. I have gotten the most improvement from a SLIGHT adjustment to the float. I put a couple more marks on the balancer so I could see where I'm sitting on mechanical advance. She ain't perfect, but she's getting better and is at least driveable!! Thank you all for the advice.
 
4spdcuda66 said:
Float adjustment is spot on. Accelerator pump is set right and squirting as it should. I can let it take off on its own, get up to 15 mph or so and hit the brakes with no stalling in forward or reverse. If I hit the gas to take off and then hit the brake it stalls forward or reverse. The two metering screws at the base of the carb are backed out 1-1/2 turns from seated. I don't have a clue as to what's going on with it.
Click to expand...

Reduce the pump shot, reduce the idle-timing and increase the idle rpm.
The reduced idle-timing will require an increased butterfly opening to maintain a decent idle speed (minimum 600/650 in gear.
The increased butterfly opening may require a reduced mixture setting, leaning idle back to normal.
The pump shot should be reduced to the minimum amount and timing, to prevent sags in acceleration and hesitations at throttle tip-in. Any more than that is a waste of fuel. To retard the pump-timing,the arm usually has to be installed in a hole further away from the pivot, and re-bent to re-set the stroke length. You can mess with the stroke length, within the limits of the mechanical range of the linkage. Every time you change the idle speed,the stroke length is affected. The factory stroke length is set with the curb idle screw backed right out.To experience what the pump is actually doing, you can disconnect it and go for a little drive somewhere on a deserted parking lot,lol

I have seen this happen in cars with low-stall convertors, and with too-far closed throttle plates,and with too much pump shot. Under these conditions,the engine does not have enough time to burn off all the pump-shot and then when the butterflies slam shut, engine vacuum pulls in a whopping big pile of fuel, and then you get an instant flooded condition. But not the usual kind of flooded. This is only flooded for the throttle opening. The engine will start right up again, sometimes requiring just a hint of air.
Good luck.
 
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