Author Topic: At a loss - engine stalls under load  (Read 5558 times)

R68GTO

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At a loss - engine stalls under load
« on: July 04, 2022, 05:57:29 PM »
Looking for some insight on troubleshooting my engine troubles.  Car starts, idles, drives out fine until you give it any heavy throttle.  I'm not talking mash to the floor, just hard acceleration, say 1/2 to 3/4 throttle.  When you do that, engine stumbles, then dies.  Quickly restarts and runs fine at light/partial throttle.  Car will rev in neutral without issue.  Car also seems to be able to handle heavier throttle when I first take it out.  After about 1 mile of running through the gears a few times, it can't handle heavy throttle.  I started to troubleshoot, then fell into the black hole of replacing parts one at a time to no avail.  Here's what I've done/checked:
1) checked plugs - fine
2) check resistance on plug wires - fine
3) checked coil - fine
4) replaced points with electronic module / along with coil
5) checked timing - fine
6) plugged vacuum advance - no change other than difficult idling
7) changed plug wires
8) changed fuel pump

What am I missing?  BTW, it's a solid lifter 427 built to stock specs - heads, cam, carb, distributor are all OE stuff.
1969 427 COPO Camaro Lemans Blue/Black, M22 4 speed, 15,500 original miles

Steve68

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Re: At a loss - engine stalls under load
« Reply #1 on: July 04, 2022, 06:53:56 PM »
Have you checked the float levels and other carb adjustments such as the accelerator pump?

jwbavalon

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Re: At a loss - engine stalls under load
« Reply #2 on: July 04, 2022, 07:23:00 PM »
I'm with Steve on the accelerator pump.  On the "first take off" the choke is on sop lots of extra fuel.

R68GTO

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Re: At a loss - engine stalls under load
« Reply #3 on: July 04, 2022, 08:09:40 PM »
Float level is good in both bowls. 
How do you tell if accel pump is functioning correctly?
1969 427 COPO Camaro Lemans Blue/Black, M22 4 speed, 15,500 original miles

GMAD_Van Nuys

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Re: At a loss - engine stalls under load
« Reply #4 on: July 04, 2022, 08:25:06 PM »
The fuel inlet in your gas tank could be clogged with debris.

Steve68

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Re: At a loss - engine stalls under load
« Reply #5 on: July 04, 2022, 09:10:09 PM »
Float level is good in both bowls. 
How do you tell if accel pump is functioning correctly?

Engine off. Remove carb cleaner. Look down carb throat. Use a light to light up area in throat if you canít see clearly. Hold the throttle linkage in you hand and as you look down carb move the throttle as if accelerating, there should be a discharge (squirt) of gas into the throttle body area.  If you donít see gas coming out during the throttle movement then there is an issue and likely your problem.

Use a service manual or Google to see how to set the correct spacing between linkage and pump lever.

R68GTO

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Re: At a loss - engine stalls under load
« Reply #6 on: July 04, 2022, 11:36:53 PM »
Checked the access pump per Steve's suggestion....carb received a shot of fuel as soon as I moved the throttle lever.
Fuel tank is new as are the lines all the way to the carb.  I did retain the original sending unit just because it was original to the car.  It was in perfect shape and the filter sock was still pliable and not deteriorating.
1969 427 COPO Camaro Lemans Blue/Black, M22 4 speed, 15,500 original miles

Steve68

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Re: At a loss - engine stalls under load
« Reply #7 on: July 05, 2022, 12:28:02 AM »
How did you check the fuel bowl levels?

maroman

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Re: At a loss - engine stalls under load
« Reply #8 on: July 05, 2022, 01:25:23 AM »
What kind of carb?
Doug  '67 RS/SS 396 auto I know the car since new

R68GTO

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Re: At a loss - engine stalls under load
« Reply #9 on: July 05, 2022, 01:30:03 AM »
4346 GM Holley - all original parts, Erik Jackson went through it before I installed it.
1969 427 COPO Camaro Lemans Blue/Black, M22 4 speed, 15,500 original miles

David K

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Re: At a loss - engine stalls under load
« Reply #10 on: July 05, 2022, 04:10:07 AM »
Did the problem occur out of the blue?

Stingr69

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Re: At a loss - engine stalls under load
« Reply #11 on: July 05, 2022, 01:39:04 PM »
Fuel starvation sounds likely.  Filter inside carb fuel inlet needs to be looked at first.  Also, currently available fuel pumps seem to be pretty bad.

You might want to mount a fuel pressure guage at least temporarily to see if you loose pressure. 

169INDY

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Re: At a loss - engine stalls under load
« Reply #12 on: July 05, 2022, 03:20:37 PM »
 Car will rev in neutral without issue. 

I had a problem like this on a quadrajet car, turnout to be missing that darn thin metal separator gasket.

Check the vacuum values?

Might NOT apply to your Holley situ
Jim
68 SS/RS L35 Th-400 LOS
69 Pace Car L48 Th-350 LOS
68 Z28 M21 LOS

R68GTO

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Re: At a loss - engine stalls under load
« Reply #13 on: July 05, 2022, 11:31:09 PM »
Did the problem occur out of the blue?

I have been trying to recall the sequence of events.  I believe this condition started after I installed new 8.5 power valves in the carb.  I did check them before installing.
1969 427 COPO Camaro Lemans Blue/Black, M22 4 speed, 15,500 original miles

R68GTO

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Re: At a loss - engine stalls under load
« Reply #14 on: July 05, 2022, 11:32:56 PM »
Car will rev in neutral without issue. 

I had a problem like this on a quadrajet car, turnout to be missing that darn thin metal separator gasket.

Check the vacuum values?

Might NOT apply to your Holley situ

I'm not familiar with the thin metal separator gasket.  Where is it on a quadrate? Vacuum is right at 14.5 inches
1969 427 COPO Camaro Lemans Blue/Black, M22 4 speed, 15,500 original miles

 

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