Help. Engine stalls with braking
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
Help. Engine stalls with braking
I'm still having stalling issues with hard braking. 1968 427 4 speed with transistor ignition, power brakes and Quick Fuel 850 carb. Here is what I've tried to identify the problem so far:
1. Adjusted float bowls, lowered to just below the sight glasses. Still stalls. Ran a plastic tube between the bowl vents. Still stalls. Switched to my old Holley 750. Still stalls.
2.Disconnected and plugged the vacuum line to the tank. Still stalls. I must be going ten mph or more and hard brake for it to stall. If I just hit the brake pedal hard while not moving nothing happens, no blips or hiccups.
3. New transitor ignition harness, new engine harness. I even hot wired from the horn relay terminal to the ignition wire and it still stalls.
4. I've checked the battery ground and the engine block ground. They seem to be good. I ran a jumper wire from the TI box to the frame. It still stalls. None of the accessories, radio, lights cut out while braking.
I turned up the idle to 1500 rpm so now the engine just nearly dies under braking. At 1000rpm or less it will die.
I'm all out of ideas and have been struggling with this for a year. Does anyone have any suggestions?
TT
1. Adjusted float bowls, lowered to just below the sight glasses. Still stalls. Ran a plastic tube between the bowl vents. Still stalls. Switched to my old Holley 750. Still stalls.
2.Disconnected and plugged the vacuum line to the tank. Still stalls. I must be going ten mph or more and hard brake for it to stall. If I just hit the brake pedal hard while not moving nothing happens, no blips or hiccups.
3. New transitor ignition harness, new engine harness. I even hot wired from the horn relay terminal to the ignition wire and it still stalls.
4. I've checked the battery ground and the engine block ground. They seem to be good. I ran a jumper wire from the TI box to the frame. It still stalls. None of the accessories, radio, lights cut out while braking.
I turned up the idle to 1500 rpm so now the engine just nearly dies under braking. At 1000rpm or less it will die.
I'm all out of ideas and have been struggling with this for a year. Does anyone have any suggestions?
TT
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
Fuel pressure is fine. I have a new Holley pump as a result of this process. I was getting low pressure as the engine warmed up but that was due to the gage mis reading with heat. Once the plug on gage was removed, the pressure went to normal. Another case of chasing my tail when nothing was really wrong.
I am running a vacuum advance. I set it at 6 BTDC with the vacuum advance plugged. It ran at idle in this condition. But it could have moved. I can plug it off and run pure mechanical and see if this eliminates the problem.
Thanks
TT
I am running a vacuum advance. I set it at 6 BTDC with the vacuum advance plugged. It ran at idle in this condition. But it could have moved. I can plug it off and run pure mechanical and see if this eliminates the problem.
Thanks
TT
Race Director
Joined: May 2006
Posts: 18,735
Likes: 2,582
I was not intending to imply removing vacuum advance would solve the problem. I was trying to get you to run manifold vacuum to get extra timing at closed throttle.
So what is the pressure with the Holley pump, too much can also be a problem.
Did you originally have a return line and you disconnected it?
Why do you have initial timing set to such a low number?
What make and model number distributor?
So what is the pressure with the Holley pump, too much can also be a problem.
Did you originally have a return line and you disconnected it?
Why do you have initial timing set to such a low number?
What make and model number distributor?
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
You should be 10 or 12 with out vac advance , with it connected add what ever that vac pod provides 10 or whatever its rated for. Also check a few plugs make sure you are not running rich that at idle , That will extinguish the flame like you are describing . Also make sure you have NO vac leaks .. That will also cause this issue
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
Lars
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
I'm running manifold vacuum to the original TI distributor (k66).
The fuel pressure was 7 or 8 psi at idle. It was exactly what it should have been.
The carb could be running rich. It is something I can check.
Thanks
TT
The fuel pressure was 7 or 8 psi at idle. It was exactly what it should have been.
The carb could be running rich. It is something I can check.
Thanks
TT
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Do as Lars suggested and advance the timing.......this is important. Disregard the engine sticker under the hood and the Shop Manual....those timing numbers were created by lawyers in the 60's......
The only other thing I can think of is that the rockers may be too tight.......I ran into this on an offshore boat with a BBC....it would stall when you got out of it after running sustained RPM.....
We loosened the rockers one half turn and it stopped........what was happening was the engine would stop so fast the lifters would not bleed down fast enough and would hold valves open.
Jebby
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Melting Slicks
Joined: Feb 2017
Posts: 3,232
Likes: 1,232
From: PHX AZ
The 'sock' that pre-filters the fuel COULD BE 3" from the bottom of the tank. Can you correlate the stalling issue to a 'low' tank.? Fuel pressure would not reflect braking uncovering the fuel sock.
Unkahal
Unkahal
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
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From: Belmont California
I'll adjust the timing this weekend. I thought starting with 16 would put you way over the 38-42 degree max with the vac advance attached.
Does anyone know how many degrees you get from the mechanical advance and the vacuum advance from a stock 1968 390 hp transitor ignition distributor? Does the vacuum advance back down at high rpm?
Thanks,
TT
Does anyone know how many degrees you get from the mechanical advance and the vacuum advance from a stock 1968 390 hp transitor ignition distributor? Does the vacuum advance back down at high rpm?
Thanks,
TT
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
I'll adjust the timing this weekend. I thought starting with 16 would put you way over the 38-42 degree max with the vac advance attached.
Does anyone know how many degrees you get from the mechanical advance and the vacuum advance from a stock 1968 390 hp transitor ignition distributor? Does the vacuum advance back down at high rpm?
Thanks,
TT
Does anyone know how many degrees you get from the mechanical advance and the vacuum advance from a stock 1968 390 hp transitor ignition distributor? Does the vacuum advance back down at high rpm?
Thanks,
TT
Vacuum advance only works when the throttle blades are closed or almost closed....like at idle or part throttle cruising.
Set the total for 38 total at 3000 rpm. Tighten the distributor. Plug vacuum back in and go for a ride.....post your results.
Jebby
Burning Brakes
Joined: Oct 2003
Posts: 836
Likes: 26
From: Harrisburg Pa
You said you have hard braking and You said it does not stall at idle when you hit the brakes but it does at 10 mph, vacuum is highest at idle so I would check
your brake booster, the booster line is separate from your vacuum tank lines, pull the line and plug it, I bet the stall goes away, a booster leaking internally is common and will cause both of these problems.
your brake booster, the booster line is separate from your vacuum tank lines, pull the line and plug it, I bet the stall goes away, a booster leaking internally is common and will cause both of these problems.
Drifting
Joined: Sep 2019
Posts: 1,355
Likes: 635
From: St. Louis
Is this a manual transmission car? If so, do you have the clutch disengaged when hitting the brake hard? If not, the rear brakes might be grabbing and stalling the car. Just thinking outside the box......
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
It is not the timing. I set up the distributor many years ago for all in at 3000 rpm. I just checked it and it goes to 38 degrees advanced at 3000 rpm w/o vacuum advance and plugged.
The vacuum can I have is marked M5 360 12. No verifiable spec on line for this unit but, one thread said it is a B1 unit producing 16 degrees advance at the crank. At 1000 rpm with no vac advance I got 12 degrees. Attaching the vac advance and adjusting the idle to 1000rpm I measured 28 degrees so it does provide 16 degrees.
With vac advanced hooked up max advance pegged at 54 degrees. At 800rpm idle I'm at 26 degrees advanced.
I'll try disconnecting and plugging the brake booster next. Hopefully I can brake hard enough to verify this theory.
The vacuum can I have is marked M5 360 12. No verifiable spec on line for this unit but, one thread said it is a B1 unit producing 16 degrees advance at the crank. At 1000 rpm with no vac advance I got 12 degrees. Attaching the vac advance and adjusting the idle to 1000rpm I measured 28 degrees so it does provide 16 degrees.
With vac advanced hooked up max advance pegged at 54 degrees. At 800rpm idle I'm at 26 degrees advanced.
I'll try disconnecting and plugging the brake booster next. Hopefully I can brake hard enough to verify this theory.
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
It is not the brake booster. I disconnected and plugged the line and it stalls with braking. I've plugged the accessory line previously so it can't be a vacuum problem at this point.
Ive already hot wired the ignition with the positive lead. Perhaps it is a bad ground. Where would be the best place to ground the ignition? From the negative coil terminal to the frame?
Ive already hot wired the ignition with the positive lead. Perhaps it is a bad ground. Where would be the best place to ground the ignition? From the negative coil terminal to the frame?
Race Director
Joined: Jun 2000
Posts: 10,046
Likes: 675
From: FL
Ok, had an issue like this on my 496 when I ran Tripower. With the bowls all at the front, it would want to die from fuel slosh uncovering the jets.
Now, you have a QuickFuel carb. It may be set up for drag racing which means jet extensions in the secondary bowl. This would cause both the primaries and secondaries to be uncovered when you hit the brakes. May be worth pulling the bowls to check it out.
Oh, and I went for the expensive solution. EFI.
Now, you have a QuickFuel carb. It may be set up for drag racing which means jet extensions in the secondary bowl. This would cause both the primaries and secondaries to be uncovered when you hit the brakes. May be worth pulling the bowls to check it out.
Oh, and I went for the expensive solution. EFI.
1st Gear
Joined: Nov 2023
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It is not the brake booster. I disconnected and plugged the line and it stalls with braking. I've plugged the accessory line previously so it can't be a vacuum problem at this point.
Ive already hot wired the ignition with the positive lead. Perhaps it is a bad ground. Where would be the best place to ground the ignition? From the negative coil terminal to the frame?
Ive already hot wired the ignition with the positive lead. Perhaps it is a bad ground. Where would be the best place to ground the ignition? From the negative coil terminal to the frame?