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Old 07-03-2018, 02:48 AM   #1
Thatguywithaneye
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Exclamation Acceleration and Stalling Problem 72 GMC

So I recently got my 1972 GMC Sierra Grande and it had been sitting for a year and it had a terrible transmission leak so I took it to a local shop and had it rebuilt. I had only ever driven the truck twice (once a test drive around my neighborhood and the other time was to the tranny shop). Anyways I noticed the truck seemed a little under powered, but nothing too crazy.

Problem 1:
When I picked the truck up from the shop it stalled 3 times getting it out of the parking lot. The truck has the 350 engine and the TH350 automatic transmission. It was idling fine, but as soon as I put it into gear it would stall out. This had never happened before. I eventually got it off and away, but the troubles didn't stop there.

Problem 2:
As I was driving I noticed a lack of power and responsiveness. When my foot was completely on the floor It would either take off like normal or do nothing. The worst of it came when I had to climb a hill up to my neighborhood and I could barely make it up...It would not pick up any speed. As I crept along the last corner of the hill (about a 2.5 mile hill) it was at a mere 6MPH and I was in fear of it dying. Once it started to flatten out I got back up to around 25MPH.

Problem 3:
While all of this was happening there was a loud ticking sound (no not a knock) a tick or tapping sound. Not sure if related, but it was prominent coming up the hill. The truck was obviously also really loud.

So the truck has been sitting for around a year and the gas in it has been too and I'm honestly not even sure how much is in there because the gauge doesn't work. I'm not sure if that would make a huge difference or not, but the oil is in the same boat. I'm just learning about all of this stuff so anything would help.
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Old 07-03-2018, 08:13 AM   #2
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Re: Acceleration and Stalling Problem 72 GMC

I quote it often, but an old hot rodders addage is that 90% of carb problems are ignition. Not to say you don't need to work on your carburetion issues, but you should start by sorting out the ignition. It's hard to diagnose over the internet, but it sounds almost like a plug wire has come off the distributor cap or a plug. It could be a wire has burned on the exhaust as well and is shorting there.

HEI conversion would be my chosen way to take care of ignition woes. Skip White has complete distributors for $50. Get an HEI wiring pigtail, 12ga wire, and a spade connector to plug into the unfused ignition terminal on the fuse box. Run 1975-82 Corvette plug wires which run underneath the manifolds like the stock points wires but have the correct HEI terminal and boot.

Do a search here on HEI conversion here on the board. Otherwise, get a new set of points, condensor, cap, rotor, and wires and replace all the stock ignition pieces.

Only when the ignition is 100% can you hope to make any headway with the carburetor and any minor adjustments it may require.
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Old 07-03-2018, 10:34 AM   #3
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Re: Acceleration and Stalling Problem 72 GMC

I agree with Mike C, always timing first. You have to have your base right before you do anything to the engine. You're timing is too retarded. I've had the same thing happen before and bumping up the timing fixed it. Set your initial timing to 12 or 14 advanced and you'll see a much different engine. I also agree on upgrading to a HEI, but not a Skip White. I followed the hype and picked one up and it was dead on arrival. There's a reason its so cheap. You'd be better off finding one in a junkyard or spending a little money for something much better.
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Old 07-03-2018, 10:34 AM   #4
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Re: Acceleration and Stalling Problem 72 GMC

I'd check the fuel system too. Start with the simple stuff. It's cheap & easy to change filters (don't forget the one at the carb inlet if it's a Q-jet). Make sure the fuel pump is doing its job. Might need to flush out the tank and add fresh gas, and it's possible the carb might need cleaning out after sitting for a year.
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Old 07-03-2018, 11:58 AM   #5
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Re: Acceleration and Stalling Problem 72 GMC

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Originally Posted by Stocker View Post
I'd check the fuel system too. Start with the simple stuff. It's cheap & easy to change filters (don't forget the one at the carb inlet if it's a Q-jet). Make sure the fuel pump is doing its job. Might need to flush out the tank and add fresh gas, and it's possible the carb might need cleaning out after sitting for a year.
Perfect time to clean and rebuild the carb. It probably needs it regardless
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Old 07-03-2018, 01:13 PM   #6
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Re: Acceleration and Stalling Problem 72 GMC

All good suggestions, but need to back up for a second.
How did it run on the way to the transmission shop? It could be sad simple as a vacuum line left off, or something disconnected at the shop, and they should be able to help with that.
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Old 07-03-2018, 01:41 PM   #7
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Re: Acceleration and Stalling Problem 72 GMC

need a little more engine, ignition, carb, etc. info to make any suggestions here..

and do yourself a favor, pick one thing at a time to adjust / replace or you'll end up in circles..

and agree with above, trans shop should have some idea what they may have done to affect those symptoms..

they must have had some comments regarding drivability during their test drive..

based on these circumstances, I was thinking;
  • cracked distributor cap or cocked out of position
  • any plug wires pulled may have been crossed, check 18436572
  • distributor hold down may be loose or have loosened in the shop
  • vacuum modulator hose damaged or some other large vacuum leak
posting some basic specs, what you know or can prove by testing, and what you've done would help..

good luck!
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Old 07-03-2018, 02:57 PM   #8
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Re: Acceleration and Stalling Problem 72 GMC

Subscribing to this, as I feel I've had similar experiences. My opinion is worth next to nothing, but the first thing I thought was not firing on all 8 as others have suggested.

My truck is the same year, and I am pretty sure my fuel tank is gunked up. I have a quadrajet and the filter in the carb inlet had rust colored debris in it.

GOOD LUCK!
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Old 07-03-2018, 04:05 PM   #9
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Re: Acceleration and Stalling Problem 72 GMC

Quote:
Originally Posted by ncpetersc View Post
Subscribing to this, as I feel I've had similar experiences. My opinion is worth next to nothing, but the first thing I thought was not firing on all 8 as others have suggested.

My truck is the same year, and I am pretty sure my fuel tank is gunked up. I have a quadrajet and the filter in the carb inlet had rust colored debris in it.

GOOD LUCK!
Did your filter look like this?
If so, likely nothing wrong with it.
https://quadrajetparts.com/sintered-...lter-p-80.html
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Old 07-04-2018, 04:58 PM   #10
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Re: Acceleration and Stalling Problem 72 GMC

Quote:
Originally Posted by Mike C View Post
I quote it often, but an old hot rodders addage is that 90% of carb problems are ignition. Not to say you don't need to work on your carburetion issues, but you should start by sorting out the ignition. It's hard to diagnose over the internet, but it sounds almost like a plug wire has come off the distributor cap or a plug. It could be a wire has burned on the exhaust as well and is shorting there.

HEI conversion would be my chosen way to take care of ignition woes. Skip White has complete distributors for $50. Get an HEI wiring pigtail, 12ga wire, and a spade connector to plug into the unfused ignition terminal on the fuse box. Run 1975-82 Corvette plug wires which run underneath the manifolds like the stock points wires but have the correct HEI terminal and boot.

Do a search here on HEI conversion here on the board. Otherwise, get a new set of points, condensor, cap, rotor, and wires and replace all the stock ignition pieces.

Only when the ignition is 100% can you hope to make any headway with the carburetor and any minor adjustments it may require.
Thanks for the reply,
How difficult would a full HEI conversion be? I've never set timing or anything like that before.
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Old 07-04-2018, 05:00 PM   #11
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Re: Acceleration and Stalling Problem 72 GMC

Quote:
Originally Posted by Old_Gold View Post
All good suggestions, but need to back up for a second.
How did it run on the way to the transmission shop? It could be sad simple as a vacuum line left off, or something disconnected at the shop, and they should be able to help with that.
It was always sluggish to begin with, but the stalling was new. I had never attempted the big hill until after the transmission was finished. I checked the vacuum line and it is loose, but attached. I have to take it back there next week for a 15 day checkup.
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Old 07-04-2018, 05:02 PM   #12
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Re: Acceleration and Stalling Problem 72 GMC

Quote:
Originally Posted by 68 P.O.S. View Post
I agree with Mike C, always timing first. You have to have your base right before you do anything to the engine. You're timing is too retarded. I've had the same thing happen before and bumping up the timing fixed it. Set your initial timing to 12 or 14 advanced and you'll see a much different engine. I also agree on upgrading to a HEI, but not a Skip White. I followed the hype and picked one up and it was dead on arrival. There's a reason its so cheap. You'd be better off finding one in a junkyard or spending a little money for something much better.
I've never set timing before. Would this be difficult to figure out on your own or do you have a recommendation for where I could find useful information?
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Old 07-04-2018, 05:18 PM   #13
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Re: Acceleration and Stalling Problem 72 GMC

Pick your poison!
https://m.youtube.com/results?q=how%...0chevy%20&sm=1
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Old 07-04-2018, 05:19 PM   #14
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Re: Acceleration and Stalling Problem 72 GMC

Quote:
Originally Posted by Killer Bee View Post
need a little more engine, ignition, carb, etc. info to make any suggestions here..

and do yourself a favor, pick one thing at a time to adjust / replace or you'll end up in circles..

and agree with above, trans shop should have some idea what they may have done to affect those symptoms..

they must have had some comments regarding drivability during their test drive..

based on these circumstances, I was thinking;
  • cracked distributor cap or cocked out of position
  • any plug wires pulled may have been crossed, check 18436572
  • distributor hold down may be loose or have loosened in the shop
  • vacuum modulator hose damaged or some other large vacuum leak
posting some basic specs, what you know or can prove by testing, and what you've done would help..

good luck!
Thanks for the ideas. So it has the Chevy 350 engine (stock). The carb is the Rochester Quadrajet. I'm unsure of the ignition, but I would imagine it would be stock as most of the truck is.

I have done very little to the truck. I've done things like change the fuel filter, Air filter, Make sure everything is tight and connected. But as I stated before I'm just learning about this stuff.

I checked the distributor cap and it seems to be in good condition and all wires were connected. I didn't check to see if there were any in the wrong spot, but would it even drive at all if they were in the wrong order?

So here's the thing about the vacuum line. When I was replacing the fuel filter it was obviously in the way so I disconnected it and as I tugged on it it just fell off. It took pretty much no effort at all. When I went to go put it back on it barely would stay on. So the line only had about an eighth of an inch of area to go into the hole on the carb before it hit the rubber on the vacuum line. I'm not sure if that makes any sense, but I can post a photo for clarification.

If you have anymore questions I will happily answer them so I can have it running smoothly.
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Old 07-04-2018, 05:53 PM   #15
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Re: Acceleration and Stalling Problem 72 GMC

So I took it out for another drive today and I got it into gear to reverse out of my driveway just fine, but as soon as I came to a stop it died. Put it into park and started it again and put it into drive and it didn't stall. Drove it around and it still is very sluggish and under powered. One of the things I've noticed is that it will coast along fine, but when I give it gas it kind of sputters and after about 2-3 seconds it catches and starts accelerating. It feels like the RPMs are dropping when I come to a stop. I've had this happen with an old jeep I had, but in that case it was the lifters and it was only firing on 3/4 cylinders. The difference between the jeep and the truck is that the jeep would kick back up after a few second once stopped, but the truck just stays there till you give it gas.

Today I replaced the air/fuel filters as well as put in fresh gas.

Anyways that's just me rambling trying to give you an idea of what is happening.
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Old 07-10-2018, 06:54 PM   #16
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Re: Acceleration and Stalling Problem 72 GMC

Quote:
Originally Posted by Thatguywithaneye View Post
I've never set timing before. Would this be difficult to figure out on your own or do you have a recommendation for where I could find useful information?
Geezer is right on with his link to videos. They will help you greatly. You will see how easy it is. Also, read the following links to get a better understanding of how timing works. Goodluck, you got this!

http://www.camaros.org/pdf/timing101.pdf
http://www.stl-vettes.com/65Vette/co...ng_Advance.pdf
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Old 07-10-2018, 08:36 PM   #17
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Re: Acceleration and Stalling Problem 72 GMC

When my gas gauge was not working, I went to the hardware store and bought a 1/4 inch 4 foot dowel and used it as a dipstick in the gas tank to check the fuel level every now and then. You have a lot of unknowns, just some basic checking of everything is needed, such as: are all your spark plugs in good condition and not fouled, are the spark plug wires connected well, are the spark plug wires in good condition and not burned up from being against the exhaust, are points in good condition, if you look down in the carburetor (with the engine off) and move the throttle do you see gas squirting into the carburetor (you should see it squirt), does the distributor turn freely by hand (as in it is loose and could have been turning on its own to affect the timing), does applying and removing vacuum to the distributor's vacuum advance can change the idle speed (it should), check the oil condition and oil level.
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Old 07-10-2018, 09:18 PM   #18
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Re: Acceleration and Stalling Problem 72 GMC

Quote:
Originally Posted by geezer#99 View Post
Did your filter look like this?
If so, likely nothing wrong with it.
https://quadrajetparts.com/sintered-...lter-p-80.html
It definitely wasn't the bronze type.. it looked more like this

https://quadrajetparts.com/short-pap...lter-p-78.html
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Old 07-11-2018, 01:02 AM   #19
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Re: Acceleration and Stalling Problem 72 GMC

Quote:
Originally Posted by ncpetersc View Post
It definitely wasn't the bronze type.. it looked more like this

https://quadrajetparts.com/short-pap...lter-p-78.html
I recently had one of those completely plug up (age? fuel? beats me). I had installed it when I couldn't find a bronze one.
Now I'm back to a bronze filter and I will never buy another pleated paper filter for my Q-jet.
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Old 07-25-2018, 01:35 AM   #20
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Re: Acceleration and Stalling Problem 72 GMC

Update:

Turns out it was a mixture of a few things.
1)Did an HEI Conversion because the points looked terrible
2)Had the carb rebuilt (super dirty and gummy)
3)The gas was so bad it was terrible so currently trying to dilute the old stuff with some fresh stuff.

A combination of these makes the truck start and run like its 1972. Never really realized how much power it had until it was all fixed.

Next step...wiring

Thanks for everyone's help and suggestions.
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Old 07-25-2018, 10:31 AM   #21
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Re: Acceleration and Stalling Problem 72 GMC

Glad you got it working. On to the next project
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