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Username Post: 1979 GMC truck won’t stay running        (Topic#367323)
stewyman 
Newbie
Posts: 8

Reg: 12-31-21
12-31-21 11:08 AM - Post#2833555    

Truck will start if throttle floored but won’t stay running. Put a carb kit in and fuel is flowing into the carb. Not sure where else to start looking.





 


Mercedes 
Contributor
Posts: 851

Loc: Orlando Florida
Reg: 07-09-18
12-31-21 12:07 PM - Post#2833560    
    In response to stewyman

Adjust your idle mixture screws by seating them GENTLY and the back off 1.5 turns to the left. It does not sound like you have any idle circuit flowing.



Edited by Mercedes on 12-31-21 12:07 PM. Reason for edit: No reason given.

 
stewyman 
Newbie
Posts: 8

Reg: 12-31-21
01-09-22 12:39 PM - Post#2834226    
    In response to Mercedes

Thanks. I tried that and no change. I’ve changed the plugs and wires. I think there must still be something inside the carb. Maybe with the primary jets?






 
gchemist 
Member #271 Senior Chevytalk Moderator
Posts: 25635
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
01-09-22 02:13 PM - Post#2834238    
    In response to stewyman

Welcome to the site. Is the carb a stock q-jet?
Read through the air fuel section here: http://www.73-87.com/7387garage/garage_dri vetrain....


'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE


 
stewyman 
Newbie
Posts: 8

Reg: 12-31-21
01-12-22 01:09 PM - Post#2834436    
    In response to gchemist

The carb is an edlebrock 1406. I have been completely through the carb and made sure everything is cleaned out and new gaskets. I haven’t changed the needles or jets, but cleaned them. Could it be a vacuum problem? Thanks




 
gchemist 
Member #271 Senior Chevytalk Moderator
Posts: 25635
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
01-12-22 01:38 PM - Post#2834439    
    In response to stewyman

How did you tune it? You need a simple vacuum gauge. Connect it to the passenger side port. How far in are the idle mixture screws? Which pump setting is the lever on? Are you using a filter? What kind? Does it flow in only one direction? How is your choke adjusted? Does it close all the way way when cold? Does it open up once power is on?

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE


 
stewyman 
Newbie
Posts: 8

Reg: 12-31-21
01-14-22 10:04 AM - Post#2834533    
    In response to gchemist

The carb has been on for 10years. Gas tank rusted and it sat for 6 months. Started but with out much power when driving. Filter was clogging from the tank. Replaced the tank and good clean gas in filter and plenty in the carb.

I blocked off the vacuum to the brakes and on the front connected straight from the PCR and distributor. It will start and barely run if throttle is full on. Choke open or closed. I haves moved the idle screw. Pump is in the middle. Mixture screws re out 1.5 turns.



 
Mercedes 
Contributor
Posts: 851

Loc: Orlando Florida
Reg: 07-09-18
01-15-22 09:55 AM - Post#2834577    
    In response to stewyman

Sounds like your fuel lines are contaminated and blocked as well.



 
stewyman 
Newbie
Posts: 8

Reg: 12-31-21
01-18-22 08:29 AM - Post#2834773    
    In response to Mercedes

No, the fuel lines are clean. I have blown through them and there is plenty of clean gas making it to the carb.

I put a new distributor and rotor in and it will run a little longer while full throttle, but won't run on its own and spits little gas up and out of the main bowl.



 
Mercedes 
Contributor
Posts: 851

Loc: Orlando Florida
Reg: 07-09-18
01-18-22 09:12 AM - Post#2834778    
    In response to stewyman

Not to over-simplify, but an engine that old needs only three things to run. Air (compression), fuel and spark.

Have you checked the ignition timing?



 
stewyman 
Newbie
Posts: 8

Reg: 12-31-21
01-18-22 06:47 PM - Post#2834819    
    In response to Mercedes

Not sure how to check the timing without getting it to run. It feels like it is something in the carb, but not sure what else to do to it.




 
Liberty Valance 
Contributor
Posts: 137
Liberty Valance
Loc: Euless,Texas
Reg: 07-21-14
01-18-22 07:00 PM - Post#2834820    
    In response to stewyman

If you don't mind posting your location, maybe someone here could go to you and help out.

1974 Cheyenne 10 LWB STOCK 350 W/HEI /TH350 /AC/ 4 BBL Quadrajet
Mopar by Birth
Chevy by Choice


 
stewyman 
Newbie
Posts: 8

Reg: 12-31-21
01-18-22 08:22 PM - Post#2834825    
    In response to Liberty Valance

That would be great. I'm near Phoenix Arizona




 
gchemist 
Member #271 Senior Chevytalk Moderator
Posts: 25635
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
01-19-22 06:29 PM - Post#2834892    
    In response to stewyman

Check timing by setting initial timing. Cylinder 1 must be top dead center. Rotor should point at cylinder 1. Harmonic balancer should be on zero mark. The distributor may be off by one tooth. It’s easy to do. I’ve done it.

Moving to the Performance Section for more site views and help.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE


 
stewyman 
Newbie
Posts: 8

Reg: 12-31-21
01-20-22 10:21 AM - Post#2834933    
    In response to gchemist

Thank you for the help, I'll give it a try.



 
IgnitionMan 
Valued Contributor
Posts: 3934

Reg: 04-15-05
01-20-22 01:00 PM - Post#2834949    
    In response to stewyman

Also, if you haven't tried it yet, take the fuel filler cap off, and try it.

If the cap is a vent type for a vented system, the vent in the cap might be plugged with old emulsified gas.

Even if it is a closed vent system, try it, too. If it gets better, the venting lines could be plugged.

Worth a try.



 


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