Mid 70's GMC truck experts, check in here, lol

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SidewaysN2second

Senior member
Sep 19, 2001
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Hey guys, i have a 74 GMC 1/2 ton, and she's as trusty as she is rusty, hehe, anyway, i'm trying to ressurect this thing from the dead to drive as a winter vehicle, lol. Anyway, when i start it, it sounds like its running on 3 of the 8 cylinders, i'll let it run for a bit, and slowly give it more and more gas constantly and gradually, and i can feel the other cylinders kick in and out, but she's coughin and backfirin carbo all over da place, but after abotu 10 min of runnin, sounds like its runnin on at least 6 of the 8 cylinders, lol, any idea where to start? im thinkin it COULD be a timing problem, cuz as the truck gets warmer more cyls keep kickin in :p


waddya thing guys?

 
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Fatdog

Golden Member
Nov 10, 2000
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I would start with a complete tune up; cap, rotor, points, wires, plugs, time it and think about rebuilding the carb too.
 
JC

JC

Diamond Member
Feb 1, 2000
5,848
68
91
It's the choke pulloff, most likely. It's a little vacuum can that opens the choke a little after the engine starts, to prevent the over-rich condition you're describing.
 
JC

JC

Diamond Member
Feb 1, 2000
5,848
68
91


<< If it's been sitting for a long while then I would definitely suspect the points. >>



A '74 model GM should have HEI electronic ignition, first year ;)
 
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Fatdog

Golden Member
Nov 10, 2000
1,001
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76
Good call on the choke pull off. It happened on my 69 Buick GS, I forgot all about it.
 
Jeffwo

Jeffwo

Platinum Member
Mar 2, 2001
2,759
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<< I would start with a complete tune up; cap, rotor, points, wires, plugs, time it and think about rebuilding the carb too. >>



Ditto...at least get points, plugs, rotor button and cap or you are asking for trouble. Those items
will give lots of headaches and they are not expensive or complicated to replace.

Ya gotta start somewhere and ya need to eliminate these problem areas before you will be
able to see what it may actually need to be put in tip-top shape.


Thanks,
Jeff
 
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Angrymarshmello

Lifer
Apr 5, 2000
13,256
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PacFanWeb owns a "souped" up 70's model Chevy...although I'm sure most of the people in this thread know what they're talking about though
 
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SidewaysN2second

Senior member
Sep 19, 2001
501
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guys, i wont lie to ya, the truck used to haul @ss, and the problem progressively got worse and worse, but i used it just as a winter beater, and didnt care cuz i drove the firebird in the summer, well now the birds in storage, and I'm screwed, lol... anyway the truck is HORRIBLE on gas now, like 100 miles to a tank? somethin is screwed, and i found oil in the air cleaner prior to last years storage of it... I gotta ressurest this beast, as long as i dont have to go internal on her, i think i should be ok.... and she's the big 350, god it sounds SOOO awesome to hear that big 4 barrel open up and put you into the seat :)
 
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UnixFreak

Platinum Member
Nov 27, 2000
2,008
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76
Is It a quadra-puke (Oh, I am sorry, quadra-jet). If so, I definitely agree with the choke part. The 350 is a tempermental beast. When they run, they run hard, but you have to "massage" them quite a bit. Frequent use of carb cleaner deteriorates your gaskets, but is almost necessary with most 350s. Dont ask me, but you can put the same carb on a ford,
and its not the case (*not that fords are better, PLEASE do not misinterpret that statement :) ) but, that, and clean spark plugs, and adjusted rockers, all are things you need to do often with a 350. Compared to computers, engines are actually really simple. the most common problems with engines:
Fuel delivery (fuel filter, jets, muck in carb, etc CHOKE) That reminds me, replace the fuel filter. If its not the problem you are out a whopping $2.99
Ignition (spark plugs, wires, points/HEI, etc)
Major mechanical probs (rings, valves, etc)

Most of the time, its just fuel or ignition. No biggie. Not nearly as complex as trying to figure out why your computer reboots when you go near the shed in Ghost Recon.

Check that fuel filter, and the choke.
 
JC

JC

Diamond Member
Feb 1, 2000
5,848
68
91


<< *not that fords are better >>



hey HEY I am driving a Ford truck right now........ ;)

btw don't need to adjust rockers with hydraulic camshaft.
 
C

CraigRT

Lifer
Jun 16, 2000
31,440
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<< Not nearly as complex as trying to figure out why your computer reboots when you go near the shed in Ghost Recon. >>



hahahahahaha.....
 
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SidewaysN2second

Senior member
Sep 19, 2001
501
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i hear that, fuel filter is new, how much do you think new cap rotors plugs etc would run me? as well as that vacum can dealie?

hehe i used to pimp in that thing! i had a panasonic CQDF 800 U CD player in it, 2 12" cerwin vegas, and a set of 6x9's, Silver window tint too! heheh dont bother locking the doors cuz a thief could just climb in thru the hole in the floor and steal the system! hhehe, sad thing is that 74 rusted out GMC has seen more booty then my 95 firebid ever has! hahah!
 
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UnixFreak

Platinum Member
Nov 27, 2000
2,008
0
76


<< btw don't need to adjust rockers with hydraulic camshaft. >>




You still do. Believe me. This is a common misconception.
 
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SexEPid

Platinum Member
Aug 1, 2000
2,115
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Reg, that's society telling you the GMC should have seen less booty than your Firebird...

Pid
 
E

etech

Lifer
Oct 9, 1999
10,597
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"i found oil in the air cleaner prior to last years storage of it"

I'd replace the PCV valve also and check the tubing to make sure it is not plugged up.

edit or is that the EGR valve?



EGR
Now we understand why it is there. And we understand what it does. So what can go wrong with it and what are the symptoms??

It's really pretty simple - it can be open when it isn't supposed to be, or it can be closed when it is supposed to be open. Not rocket science, but it is science. If it is open when it is not supposed to be open, at idle for instance, It will act like one monster vacuum leak and the engine will not idle or will idle really roughly. If it doesn't open when it is supposed to open you will probably experience a symptom of "pinging" or "knocking" since the combustion chamber temperature will be higher than normal (one of the main causes of pinging in an engine).

 
JC

JC

Diamond Member
Feb 1, 2000
5,848
68
91


<<

<< btw don't need to adjust rockers with hydraulic camshaft. >>




You still do. Believe me. This is a common misconception. >>



No, believe me, if you run at least 1/2 turn preload, you won't need to adjust them unless your camshaft goes flat. Or you have other faulty/loose parts.
 
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Brutuskend

Lifer
Apr 2, 2001
26,558
4
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Well the warmer it gets the better it runs?

Sounds like it could be a vacuum leak.

When the engine warms up, the parts expand and the vacuum leak starts to go away, then it runs better.

To check for leaks, get a can of starting fluid, or carb cleaner and spray it around the base of the carb. and intake manifold (while it's running) it the engine speed's up, you have a leak!
 
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SidewaysN2second

Senior member
Sep 19, 2001
501
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k, sprayed carb cleaner in and got a bunch of crap out, but truck still runs like crap and backfires, burns a retarted ammount of gas! i burnt an 1/8 tank idling it for like 15 min! as best i can see, there are 3 canister dealies, theres the one on the carb for the choke, 1 on the right hand side of the engine on the intake manifold, and one at the rear almost by the distributor cap. i have an old truck in the bush, could i rape the parts off thee and swap them? is it one of these things thats givin me grief? a pic of the culprit would help!
 
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