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#1 |
Registered User
Join Date: Oct 2017
Location: Kamloops BC, Canada
Posts: 20
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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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#2 |
Registered User
Join Date: Dec 1999
Location: Austin, TX, USA
Posts: 7,717
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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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44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax |
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#3 |
Registered User
Join Date: Jan 2007
Location: Puyallup, WA
Posts: 1,662
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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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72 C10 lwb fleetside -stock 350/350 combo |
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#4 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,637
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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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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#5 | |
Registered User
Join Date: Jan 2007
Location: Puyallup, WA
Posts: 1,662
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Re: Acceleration and Stalling Problem 72 GMC
Quote:
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72 C10 lwb fleetside -stock 350/350 combo |
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#6 |
Registered User
Join Date: Jan 2017
Location: Mason City, IA
Posts: 157
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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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#7 |
Registered User
Join Date: Jan 2016
Location: Barber City, CA
Posts: 4,782
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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;
good luck!
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I started out with nothing - and I still have most of it |
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#8 |
Registered User
Join Date: Jun 2018
Location: Fuquay-Varina, NC (Just outside of Raleigh)
Posts: 237
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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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#9 | |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,621
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Re: Acceleration and Stalling Problem 72 GMC
Quote:
If so, likely nothing wrong with it. https://quadrajetparts.com/sintered-...lter-p-80.html |
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#10 | |
Registered User
Join Date: Oct 2017
Location: Kamloops BC, Canada
Posts: 20
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Re: Acceleration and Stalling Problem 72 GMC
Quote:
How difficult would a full HEI conversion be? I've never set timing or anything like that before. |
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#11 |
Registered User
Join Date: Oct 2017
Location: Kamloops BC, Canada
Posts: 20
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Re: Acceleration and Stalling Problem 72 GMC
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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#12 | |
Registered User
Join Date: Oct 2017
Location: Kamloops BC, Canada
Posts: 20
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Re: Acceleration and Stalling Problem 72 GMC
Quote:
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#13 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,621
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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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#14 | |
Registered User
Join Date: Oct 2017
Location: Kamloops BC, Canada
Posts: 20
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Re: Acceleration and Stalling Problem 72 GMC
Quote:
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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#15 |
Registered User
Join Date: Oct 2017
Location: Kamloops BC, Canada
Posts: 20
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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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#16 | |
Registered User
Join Date: Jan 2007
Location: Puyallup, WA
Posts: 1,662
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Re: Acceleration and Stalling Problem 72 GMC
Quote:
http://www.camaros.org/pdf/timing101.pdf http://www.stl-vettes.com/65Vette/co...ng_Advance.pdf
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72 C10 lwb fleetside -stock 350/350 combo |
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#17 |
Senior Member
![]() Join Date: Apr 2016
Location: Cypress, TX
Posts: 3,711
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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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#18 | |
Registered User
Join Date: Jun 2018
Location: Fuquay-Varina, NC (Just outside of Raleigh)
Posts: 237
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Re: Acceleration and Stalling Problem 72 GMC
Quote:
https://quadrajetparts.com/short-pap...lter-p-78.html |
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#19 | |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,637
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Re: Acceleration and Stalling Problem 72 GMC
Quote:
Now I'm back to a bronze filter and I will never buy another pleated paper filter for my Q-jet.
__________________
- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#20 |
Registered User
Join Date: Oct 2017
Location: Kamloops BC, Canada
Posts: 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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#21 |
Registered User
Join Date: Jan 2007
Location: Puyallup, WA
Posts: 1,662
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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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72 C10 lwb fleetside -stock 350/350 combo |
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1972, 350, gmc, noob, th350 |
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