1972 GMC 400 BB stalling at stop light - The 1947 - Present Chevrolet & GMC Truck Message Board Network

10BamBam01 · 05-30-2015, 09:59 AM

Truck runs fine at first few miles. Then the idle will drop too low at a stop light and it will die. I have adjusted timing and set the idle speed higher so that when it goes in gear it will still run. Idle is set to 900 or so in Park and then in Drive it's at 650. When the engine warms up is when the problem starts. It will periodically "sputter" or gasp when going down the street, especially when I just touch the accelerator.

I recently put new HEI dist, new plug wires, checked for vac leaks, checked vac pressure and timing. Can't figure this out. Any ideas?

hilandr452 · 05-30-2015, 10:04 AM

Did you run a new hot wire to the distributor, or are you running off the line with a ballast resistor? That will cut your juice down several volts and ignition will be weak.

geezer#99 · 05-30-2015, 10:38 AM

Put some timing in it!
Then turn down that idle. At 900 you're kicking in the mechanical in the dizzy.

**68350** · 05-30-2015, 10:43 AM

What's your timing set at?

05-30-2015, 09:59 AM	#1
10BamBam01 Registered User Join Date: Jul 2013 Location: Cedar Rapids, IA Posts: 22	1972 GMC 400 BB stalling at stop light Truck runs fine at first few miles. Then the idle will drop too low at a stop light and it will die. I have adjusted timing and set the idle speed higher so that when it goes in gear it will still run. Idle is set to 900 or so in Park and then in Drive it's at 650. When the engine warms up is when the problem starts. It will periodically "sputter" or gasp when going down the street, especially when I just touch the accelerator. I recently put new HEI dist, new plug wires, checked for vac leaks, checked vac pressure and timing. Can't figure this out. Any ideas?

05-30-2015, 10:04 AM	#2
hilandr452 Registered User Join Date: Jan 2009 Location: Colorado Springs, CO Posts: 357	Re: 1972 GMC 400 BB stalling at stop light Did you run a new hot wire to the distributor, or are you running off the line with a ballast resistor? That will cut your juice down several volts and ignition will be weak. __________________ Dan Smith Colorado Springs, CO 71 GMC Custom Camper "Longhorn" 454, TH400 73 Chevy Camper Special (Yes, it's badged a camper special) Flat Bed Motorhome conversion 454, standard tranny *"DON'T TREAD ON ME !!!"* My Project: http://www.picturetrail.com/sfx/album/view/20829244 , http://www.picturetrail.com/sfx/album/view/24654442

05-30-2015, 10:38 AM	#3
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,731	Re: 1972 GMC 400 BB stalling at stop light Put some timing in it! Then turn down that idle. At 900 you're kicking in the mechanical in the dizzy.

05-30-2015, 10:43 AM	#4
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: 1972 GMC 400 BB stalling at stop light What's your timing set at? __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi



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