Carb Rebuild Needed?
11-15-2016, 04:52 PM
#1
Melting Slicks
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Carb Rebuild Needed?
'79 L82 with 53k. Stock except for true dual exhaust and an Edelbrock "Performer" intake manifold. Save the catalytic converter, all factory emission controls are installed and verified as functioning properly. Original dual snorkel cold air intake system with all components. I've verified that the fuel bowl is not emptying after sitting for extended periods as I still get nice squirts from both primary jets.
I've replaced the plugs, wires, fuel filter, rotor and distributor cap and all have no more than 1,000 miles. All of the vacuum hoses in the car (save the HVAC system) very recently replaced with kits from Doc Rebuild.
Upon my purchase the carburetor appeared untouched. The primaries were filthy and the exterior of the rather dirty. The original chromate finish was intact. I used a couple cans of spray carb/choke cleaner and while it removed much of the original exterior finish there were some improvements.
Problems that remain:
1) Inconsistent cold starts. Sometimes perfect per factory instructions: two times (slowly) to the floor, let up accelerator and crank. When "happy" such starts are instant. If it does not start this way it is pump, pump, pump and crank, crank, crank as the "repeat" (two times to floor) does not work. On rare occasion this causes a flooded condition that will not clear. If it's been sitting a long time and the battery is weak I sometimes resort to a spray of starting fluid. I've verified that the choke plates are closing properly with a cold engine and that the initial vacuum pull-off functions.
2) Inconsistent idle speed with incredibly touchy adjustment. This happens both with and without A/C operating. The A/C solenoid functions.
3) High idle that works when it wants to.
4) What I believe to be slow increase to red line at WOT. It's an automatic and while I get decent acceleration from a stop in "drive" it takes a ridiculous amount of time for the RPM to get near red line when I operate the shifter manually. The only time I see high RPMs is with an automatic downshift when already at 40+mph.
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Am I correct that these symptoms combined with what I've already done lead to "rebuild the carburetor?"
I've received some excellent info from Lars and find his price quite reasonable but I just want to verify that my logic is correct as I haven't dealt with a carbureted car since I was a kid. I did rebuild a Quadrajet (1971 Chevelle) when I was 16 years old but my uncle had to get it truly working. If I remember properly he said that I'd done a very good job for a kid with few tools reading the instructions that came with the carb kit but it was terribly adjusted.
I've replaced the plugs, wires, fuel filter, rotor and distributor cap and all have no more than 1,000 miles. All of the vacuum hoses in the car (save the HVAC system) very recently replaced with kits from Doc Rebuild.
Upon my purchase the carburetor appeared untouched. The primaries were filthy and the exterior of the rather dirty. The original chromate finish was intact. I used a couple cans of spray carb/choke cleaner and while it removed much of the original exterior finish there were some improvements.
Problems that remain:
1) Inconsistent cold starts. Sometimes perfect per factory instructions: two times (slowly) to the floor, let up accelerator and crank. When "happy" such starts are instant. If it does not start this way it is pump, pump, pump and crank, crank, crank as the "repeat" (two times to floor) does not work. On rare occasion this causes a flooded condition that will not clear. If it's been sitting a long time and the battery is weak I sometimes resort to a spray of starting fluid. I've verified that the choke plates are closing properly with a cold engine and that the initial vacuum pull-off functions.
2) Inconsistent idle speed with incredibly touchy adjustment. This happens both with and without A/C operating. The A/C solenoid functions.
3) High idle that works when it wants to.
4) What I believe to be slow increase to red line at WOT. It's an automatic and while I get decent acceleration from a stop in "drive" it takes a ridiculous amount of time for the RPM to get near red line when I operate the shifter manually. The only time I see high RPMs is with an automatic downshift when already at 40+mph.
---------------------------
Am I correct that these symptoms combined with what I've already done lead to "rebuild the carburetor?"
I've received some excellent info from Lars and find his price quite reasonable but I just want to verify that my logic is correct as I haven't dealt with a carbureted car since I was a kid. I did rebuild a Quadrajet (1971 Chevelle) when I was 16 years old but my uncle had to get it truly working. If I remember properly he said that I'd done a very good job for a kid with few tools reading the instructions that came with the carb kit but it was terribly adjusted.
11-16-2016, 12:33 PM
#2
1. The inconsistent cold starts, what is the time period between when the car last ran and your attempt to start? It starts right up after 24 hours but over multiple days it gives you a hard time as an example?
2. Are you adjusting the idle speed on a fully warmed engine, with the car in drive or reverse with the wheels chocked?
3. The high idle is directly related to how far the choke closes, the more closed the higher the speed, there is cam with ramps that holds the throttle open connected to the choke linkage.
4. With the engine off, have someone step fully on the gas pedal while you check the throttle linkage to see if the cable is fully opening the throttle.
2. Are you adjusting the idle speed on a fully warmed engine, with the car in drive or reverse with the wheels chocked?
3. The high idle is directly related to how far the choke closes, the more closed the higher the speed, there is cam with ramps that holds the throttle open connected to the choke linkage.
4. With the engine off, have someone step fully on the gas pedal while you check the throttle linkage to see if the cable is fully opening the throttle.
Last edited by MelWff; 11-16-2016 at 12:34 PM.
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11-16-2016, 01:36 PM
#3
Melting Slicks
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1. The inconsistent cold starts, what is the time period between when the car last ran and your attempt to start? It starts right up after 24 hours but over multiple days it gives you a hard time as an example?
2. Are you adjusting the idle speed on a fully warmed engine, with the car in drive or reverse with the wheels chocked?
3. The high idle is directly related to how far the choke closes, the more closed the higher the speed, there is cam with ramps that holds the throttle open connected to the choke linkage.
4. With the engine off, have someone step fully on the gas pedal while you check the throttle linkage to see if the cable is fully opening the throttle.
11-16-2016, 02:56 PM
#4
1. That symptom could be leaking bottom plugs, the gas draining back out due to siphoning action (a inlet filter with a check valve would eliminate that) or evaporation.
2. You have checked for a vacuum leak at the carburetor base gasket or any cracked vacuum lines?
3. May need more cleaning of the linkage.
2. You have checked for a vacuum leak at the carburetor base gasket or any cracked vacuum lines?
3. May need more cleaning of the linkage.
11-16-2016, 03:45 PM
#5
Melting Slicks
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1. That symptom could be leaking bottom plugs, the gas draining back out due to siphoning action (a inlet filter with a check valve would eliminate that) or evaporation.
2. You have checked for a vacuum leak at the carburetor base gasket or any cracked vacuum lines?
3. May need more cleaning of the linkage.
11-16-2016, 03:53 PM
#6
Melting Slicks
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One other thing to add:
When I went to replace the fuel filter a few months after it was new to me, I found no filter installed! As the previous owner had died I have no idea how long it went that way. I suspect however that he (or someone for him) had recently replaced the intake manifold as it was almost new looking. Whoever did the job certainly wasn't a mechanic by any stretch of the word as they had no knowledge of flare wrenches. The fuel line between the pump and carb was replaced with rubber and the vacuum line to the brake booster was so twisted I'm amazed that it both worked and didn't leak.
When I went to replace the fuel filter a few months after it was new to me, I found no filter installed! As the previous owner had died I have no idea how long it went that way. I suspect however that he (or someone for him) had recently replaced the intake manifold as it was almost new looking. Whoever did the job certainly wasn't a mechanic by any stretch of the word as they had no knowledge of flare wrenches. The fuel line between the pump and carb was replaced with rubber and the vacuum line to the brake booster was so twisted I'm amazed that it both worked and didn't leak.
11-16-2016, 05:57 PM
#7
Le Mans Master
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Well if you removed the cat then all you need is to clamp an air/fuel monitor senor into the tailpipe for tuning the carb. And for idle and cruise rpm all you need is a narrow band A/F monitor. What I'm saying is A/F monitors don't lie and narrow band monitor are cheap as pocket change. Cheaper than a new or even rebuilt carb.
If you still have the cat then you need to install a bug on the exhaust upstream of the cat.
Good luck and please post what works for you.
If you still have the cat then you need to install a bug on the exhaust upstream of the cat.
Good luck and please post what works for you.
11-16-2016, 07:31 PM
#8
Race Director
I read this thread...and I will add this.
I have had Corvettes in my shop that were also super touchy. And what I have found is regardless if the fuel squirts when it has sat for a week..I always allow the engine to spin for a few seconds to make sure that blow is full. The I pump it twice to set eh choke and crank it Because you could be using up the last two squirts and have a dry bowl. So it runs for a second or two and dies because the fuel has not yet made it to the bowl.
I would have to make sure the choke was operating correctly every time and that the fast idle was consistent.
I am NOT a profession Quadra-Jet rebuilder. So I can not 100% confirm if you have an internal problem ...such as the emulsion tubes. etc.
Logic would tell me that if you can crank it and it work great every day....then the problem may not be internal.
When it does 'act right'..as it should...then I doubt that you have any problems with timing and other factors. Because bad vacuum hoses, incorrect timing or sticking advacne weights or advance mechanism would cause a 'hard start problem' but it to be like that all the time.
I doubt it is a fuel leak issue in the main body...where fuel is leaking in the intake. But I would not rule that out either. I would have to rasie the carb up and check myself.
DUB
I have had Corvettes in my shop that were also super touchy. And what I have found is regardless if the fuel squirts when it has sat for a week..I always allow the engine to spin for a few seconds to make sure that blow is full. The I pump it twice to set eh choke and crank it Because you could be using up the last two squirts and have a dry bowl. So it runs for a second or two and dies because the fuel has not yet made it to the bowl.
I would have to make sure the choke was operating correctly every time and that the fast idle was consistent.
I am NOT a profession Quadra-Jet rebuilder. So I can not 100% confirm if you have an internal problem ...such as the emulsion tubes. etc.
Logic would tell me that if you can crank it and it work great every day....then the problem may not be internal.
When it does 'act right'..as it should...then I doubt that you have any problems with timing and other factors. Because bad vacuum hoses, incorrect timing or sticking advacne weights or advance mechanism would cause a 'hard start problem' but it to be like that all the time.
I doubt it is a fuel leak issue in the main body...where fuel is leaking in the intake. But I would not rule that out either. I would have to rasie the carb up and check myself.
DUB
11-17-2016, 09:40 AM
#9
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When you found no filter in the inlet, was the internal spring also missing?
Do you have the instructional paper "Off Vehicle Carburetor Service" #50-505-3 also included, #50-526-8? This paper also includes the 1979-1985 data table. I'm also no expert, but found setting up the fast idle cam off car was much easier and will get you in the ballpark. Another thing is to make sure your hot air choke housing is not binding the intermediate choke shaft. A binding shaft will also effect how the fast idle cam and counter weight works.
If you have the Service Manual for your car it only includes a brief on car service section.
Do you have the instructional paper "Off Vehicle Carburetor Service" #50-505-3 also included, #50-526-8? This paper also includes the 1979-1985 data table. I'm also no expert, but found setting up the fast idle cam off car was much easier and will get you in the ballpark. Another thing is to make sure your hot air choke housing is not binding the intermediate choke shaft. A binding shaft will also effect how the fast idle cam and counter weight works.
If you have the Service Manual for your car it only includes a brief on car service section.
Last edited by bmotojoe; 11-17-2016 at 10:08 AM.
11-17-2016, 05:41 PM
#10
Race Director
Setting and adjusting the 'fast idle' when the carb is still installed is not that hard...if you know where it is and have a good flashlight and screwdriver...it is not hard to do at all.
I wrote this so people do not feel that they need to remove the carb to set the fast idle on a QuadraJet.
DUB
I wrote this so people do not feel that they need to remove the carb to set the fast idle on a QuadraJet.
DUB
11-17-2016, 07:41 PM
#11
Melting Slicks
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When you found no filter in the inlet, was the internal spring also missing?
Do you have the instructional paper "Off Vehicle Carburetor Service" #50-505-3 also included, #50-526-8? This paper also includes the 1979-1985 data table. I'm also no expert, but found setting up the fast idle cam off car was much easier and will get you in the ballpark. Another thing is to make sure your hot air choke housing is not binding the intermediate choke shaft. A binding shaft will also effect how the fast idle cam and counter weight works.
If you have the Service Manual for your car it only includes a brief on car service section.
Do you have the instructional paper "Off Vehicle Carburetor Service" #50-505-3 also included, #50-526-8? This paper also includes the 1979-1985 data table. I'm also no expert, but found setting up the fast idle cam off car was much easier and will get you in the ballpark. Another thing is to make sure your hot air choke housing is not binding the intermediate choke shaft. A binding shaft will also effect how the fast idle cam and counter weight works.
If you have the Service Manual for your car it only includes a brief on car service section.
11-17-2016, 07:44 PM
#12
Melting Slicks
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Thanks all!
It's looking more and more like I just need to remove the carb and do some more careful cleaning before considering the rebuild.
I'm having a problem with a pinched nerve at present so projects I'd already planned to do are being put off until I get a diagnosis and know if the problem is in my neck (had one there+surgery before) or (if lucky) in my shoulder.
It's looking more and more like I just need to remove the carb and do some more careful cleaning before considering the rebuild.
I'm having a problem with a pinched nerve at present so projects I'd already planned to do are being put off until I get a diagnosis and know if the problem is in my neck (had one there+surgery before) or (if lucky) in my shoulder.