Engine Stall when heavy braking

[zach0]

My engine keeps stall when I hit the brake at a moderatley fast pace but not to exteme. medium pressure. I have no accessories and am using an electric fuel pump on top of the gas tank???? 4 wheel drum with the 750 edelbrock carb (I know, its all I had)

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66 Mustang Black W/ Black
289 Hi-Po 65'heads, MSD
Lunati High lift Cam
750CFM Carb Heddman Headers, Hurst Shifter

[Gearhead999]

Did you check the float level?? Also, the curb idle.

[zach0]

I dont know any thing about carbs. I do also have a problem every once in a while with it almost wanting to stall when I step down on the pedal but then it catches and goes with no problems


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66 Mustang Black W/ Black
289 Hi-Po 65'heads, MSD
Lunati High lift Cam
750CFM Carb Heddman Headers, Hurst Shifter

[macx]

stepping on the throttle resulting in a bog means the accelerator pump is either bad or needs to "come on" quicker, esp if it happens at lower rpms more than higher. If you have power brakes, the engine bog when stepping on the brakes could be a vac leak within the power booster (your brakes wouldn't have much "power assist"). Otherwise (or also),your carb float level could be low. In fact, the acceleration bog could also be caused by low float level - not allowing the accelerator pump enuf gas to function properly. Last, do a simple but thorough vacuum leak check - all your vac hoses (check for breaks, hard ends that don't fit tight on the nipples, etc)

[zach0]

How do I adjust the float and what lvel would I put it at. No power brakes or power accessories or A/C. 750 Edelbrock #1407

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66 Mustang Black W/ Black
289 Hi-Po 65'heads, MSD
Lunati High lift Cam
750CFM Carb Heddman Headers, Hurst Shifter

[Mercury]

A big bog on a carburated car, when the gas is stepped on could also be a timing, and vacum advance issue.

Same thing with a engine that dies if you let off the gas real quick when its under heavy loads.

[thunderbolt]

You have a lot of carb for a 289. With a 750 you will not see the throttle response of a 600 because of the volume difference. However the bog issue could be several things like other people have mentioned. Does it happen all the time or only some of the time, hot or cold? You may need to adjust the accelerator pump to give you the proper boost of gas when you step on the gas. I think a bad float level might have an effect here too as well as maybe being the stalling problem. You don't have power brakes do you? If so it could be a bad booster causing a vac leak when you hit the brakes.

[Mercury]

A leak in the Vacum brake booster would be REALLY obvious. When a break booster goes out on these power brake vehicles, it takes like HE-MAN like leg muscles to press the brake pedal.

Is it a BOG, a FLAT SPOT, or hesitation? Each sympton has diffrent causes.

I just noticed you have MSD ignition,I should of noticed earlier. What do you have the timing set at also?

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64 1/2 "D" code Red Mustang Coupe. 289, C4, Mallory duel point. Ported & Polished 65 heads shaved .01 with 351 valves, 11:1 comp, 1.7:1 rockers, blue wolverine lumpy cam, modified 4100 Hipo 4 barrel. GT Apperance pkg. And to many others to list

2000 Perf Red Mustang GT. 5spd. BBK Underdrive pulleys, Flotech off-road H pipe. Hurst T-Handle, 40 series Flowmasters, Steeda Tri-Ax
64 1/2 red 6cyl coupe. Future resto.

[This message has been edited by Mercury (edited 08-31-2001).]

[thunderbolt]

Mercury:
I have witnessed a brake booster that had a small tear in the inner bladder that did not fail completely yet was a source of vacuum leak. The brake pedal was no good indicator of the problem as for the most part it still felt like power brakes.

[zach0]

No Power any thing accessories. Just MSD is the power under their. I have my timing at 13 degrees.

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66 Mustang Black W/ Black
289 Hi-Po 65'heads, MSD
Lunati High lift Cam
750CFM Carb Heddman Headers, Hurst Shifter

[Gearhead999]

To check the accel. pump. Turn off engine, pull air cleaner, climb up on engine so you can see down in through the top of the carb. Now move the throttle open and watch for the squirt of gas from the pump. If you don't see it or it doesn't start right away it needs attention.

To set the floats. You have to remove the top of the carb and hold it upside down. Then measure the distance from the gasket to the heel of the float. To raise/lower the level you bend the tang that goes from the pivot to the foat it self. Don't push the foat up or down. All you do there is force the needle into the seat and screw it up. Take a small set of needle nose pliers and hold the tang while moving the float so not to put pressure on needle and seat.

The spec for the floats on all Edelbrock carbs is 11/32".

[Brian Browning]

Different car and carb (it was a holley) but I was getting those symptoms when I had crud in the tank that was getting between the needle and seat and flooding the carb. It would bog and die if I stomped on the brakes.

[zach0]

How do you fix that

[Brian Browning]

The needle comes out from the front (and top) on a holley. There is a screw on top of the fuel bowl. You remove it, then you can turn the needle and seat out by hand. Blow it clean with carb cleaner and put it back. If you don't get it back into the same spot, you may have to adjust the float (already covered in this topic).
After doing it a few times, it takes 5 minutes. I had to go through a couple of fuel filters before I got the crud out of the tank.

[PKRWUD]

As far as stalling during hard braking, that is a classic sign of a vacuum leak, regardless of the type of brakes you have. If you have a propane torch, turn it on (with no flame) and run it around your gasket surfaces. Listen for an increase in RPM's.

Take care
~Chris

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