Corvette Forum : DigitalCorvettes.com Corvette Forums banner

1 - 20 of 51 Posts

·
Registered
Joined
·
266 Posts
Discussion Starter #1
Been many years since I rebuilt the OE Computer Carb on my 81 and I can't even remember where I got the 'special' rebuilt kit from or where all the stinking notes and procedures I had to follow and perform are.
I do recall using an old Analog DWELL METER for adjusting something on the Carb...a Dwell Meter of all things!
I know Holley's 4150 like the back of my hand, but the OE Carb on my 81 just irritates the f*ck out of me.
Wish I could tear it of and burn the damn thing and install a Holley but then I can't use the OE Air Filter and cool Air Intakes.
Also though about going Fuel Injection...give me some feedback who has done it, what manufacture and how reliable it is.
***Symptoms...all of a sudden Engine Idles like crap and it's just a coincidence it was after I filled the Tank.
Bad Gas: no, because off Idle it runs great.
Come to a Red Light, Idle drops to 500 rpm (even though I raised it) it's laboring, slight surge, vibrating and emissions/exhaust stinks bad.
Not vacuum related because: when I pull the Headlights on that Vacuum does not effect the poor idle.
A slight mist of Starting Fluid into the Carb raises idle slightly and smooths right out...so it's LEAN...the Idle circuit/maybe Float or WHATEVER is fubar. :bang
 

·
Banned
Joined
·
5,331 Posts
Been many years since I rebuilt the OE Computer Carb on my 81 and I can't even remember where I got the 'special' rebuilt kit from or where all the stinking notes and procedures I had to follow and perform are.
I do recall using an old Analog DWELL METER for adjusting something on the Carb...a Dwell Meter of all things!
I know Holley's 4150 like the back of my hand, but the OE Carb on my 81 just irritates the f*ck out of me.
Wish I could tear it of and burn the damn thing and install a Holley but then I can't use the OE Air Filter and cool Air Intakes.
Also though about going Fuel Injection...give me some feedback who has done it, what manufacture and how reliable it is.
***Symptoms...all of a sudden Engine Idles like crap and it's just a coincidence it was after I filled the Tank.
Bad Gas: no, because off Idle it runs great.
Come to a Red Light, Idle drops to 500 rpm (even though I raised it) it's laboring, slight surge, vibrating and emissions/exhaust stinks bad.
Not vacuum related because: when I pull the Headlights on that Vacuum does not effect the poor idle.
A slight mist of Starting Fluid into the Carb raises idle slightly and smooths right out...so it's LEAN...the Idle circuit/maybe Float or WHATEVER is fubar. :bang
If your unhappy with that Q-jet then get rid of it.

If your lucky enough to find install a 1970 LT-1 Q-jet.
1970 LS5 454 Q-jet.
No Emission crap.
Tuned for Raw HP.

Pontiac, Olds , And Buick made similar.
1970 for all except for Pontiac.
Good till 1974.
Later Smog Disco era 1975-79 can be made to work.
Cadillac 500 1970 Q-jet excellent too.


I like Holley 4150 these days.
Cut up that air cleaner.
Or install a Dtop base air cleaner like Moroso Racing.

Holley Terminator EFI is nice.
 

·
Registered
Joined
·
266 Posts
Discussion Starter #3
If your unhappy with that Q-jet then get rid of it.

If your lucky enough to find install a 1970 LT-1 Q-jet.
1970 LS5 454 Q-jet.
No Emission crap.
Tuned for Raw HP.

Pontiac, Olds , And Buick made similar.
1970 for all except for Pontiac.
Good till 1974.
Later Smog Disco era 1975-79 can be made to work.
Cadillac 500 1970 Q-jet excellent too.


I like Holley 4150 these days.
Cut up that air cleaner.
Or install a Dtop base air cleaner like Moroso Racing.

Holley Terminator EFI is nice.
Thanks for the feedback
Many years ago I did buy a very used non computer Q-Jet, it's been bouncing around under my workbench for over ten years. The thing looks rough but may be usable.
But then I would need a regular HEI distributor and what about the 'Check Engine' light the Computer will be throwing-up because it's not getting any feedback?
As for the "Holley Terminator EFI" ... how do I get around the Trans Kickdown linkage found on the OE Carbs passenger side, and I'm guessing the FI wants an electric Fuel Pump?
 

·
Banned
Joined
·
5,331 Posts
Thanks for the feedback
Many years ago I did buy a very used non computer Q-Jet, it's been bouncing around under my workbench for over ten years. The thing looks rough but may be usable.
But then I would need a regular HEI distributor and what about the 'Check Engine' light the Computer will be throwing-up because it's not getting any feedback?
As for the "Holley Terminator EFI" ... how do I get around the Trans Kickdown linkage found on the OE Carbs passenger side, and I'm guessing the FI wants an electric Fuel Pump?

Yes you will need a 1975-1979 GM Chevy V8 HEI with the 4-pin ignition module.


Disable the ECM.
Cut it out of the car if you want to.


The TH 350 kickdown arm is pretty easy to setup on another carb.
Holley carb has that provision typical.
I you have a 700R4 you will need a PATC conversion kit.
Or a Bow Tie Overdrive TV Cable kit.
 

·
Banned
Joined
·
5,331 Posts
Yes the Holley EFI Throttle body kit uses a High pressure fuel pump.
If your intimidated call around local with the Race shops for quote to install.
$500-750 Likely.
 

·
Banned
Joined
·
5,331 Posts
If you like Tinkering with carbs a Holley Street Avenger 4150 is an excellent choice.


Race 4150 Double Pumper will require a 3000-4500 rpm stall if an auto trans & 3.90-4.88 gears in the rear diff to get best results.


Street Avenger Holley is a 4150 with vacuum secondary.
As long as you have 3.08 gears or lower ( higher Numerical) it works with any gear on the street.
 

·
Banned
Joined
·
5,331 Posts
That Quadrajet with its electronic Arenoid solenoid is bad joke.


They are a pain.
I rebuilt many back in the day.
Still have factory Kent Moore GM service tools here somewhere for them.


Be sure to ditch it.
Be much happier......:cheers:
 

·
Premium Member
Joined
·
4,668 Posts
I do recall using an old Analog DWELL METER for adjusting something on the Carb...a Dwell Meter of all things!
I was 35 and working on these when they first came out. Wow......long time ago and yes, you should use a dwell meter, of all things and it should be set to the 6 cylinder position.

When you first turn on the ignition do you hear the carb "clicking" about 8-10 times a second? That is the sound of the metering rod moving up and down. If the solenoid goes bad it will fail to move the metering rod up and the condition will be lean. If I recall, you can read the voltage to the solenoid by putting your meter on the AC scale. Although the voltage is DC the pulsating will make it read as an AC voltage. You didn't say how it runs at wide open throttle. That WOT condition will bypass all the fuel metering stuff.

If the o2 sensor, TPS sensor are sending the wrong info to the computer it can also pull timing way back. With the age of the car I'd check th operation of the TPS first. A multimeter set on the Ohms scale should read the voltage sent to the computer. Read voltage between the blue and black wires. Slowly open the throttle and look for a smooth sweep of the meter.

I believe that this is a good place to start if you want to keep your system stock.

If you want to upgrade then look into the Holley Sniper system. It looks just like a carb and all the sensors and injectors are internal. It also has an internal computer and is self-learning. Very easy to set up. I think you'll need three wires. On hot all the time, one switched 12V wire and a ground. A little creativity should take care of the tranny issue.
 

·
Banned
Joined
·
5,331 Posts
All Quadrajets are either 750 cfm or 800 cfm.


Chevy always used the 750 cfm version.
When they wanted real Power on a Corvette a Holley 4-BBL was chosen.
Ditto for the 1970 SS Chevelle LS6 454 450 HP.
 

·
Registered
Joined
·
266 Posts
Discussion Starter #12
I was 35 and working on these when they first came out. Wow......long time ago and yes, you should use a dwell meter, of all things and it should be set to the 6 cylinder position.

When you first turn on the ignition do you hear the carb "clicking" about 8-10 times a second? That is the sound of the metering rod moving up and down. If the solenoid goes bad it will fail to move the metering rod up and the condition will be lean. If I recall, you can read the voltage to the solenoid by putting your meter on the AC scale. Although the voltage is DC the pulsating will make it read as an AC voltage. You didn't say how it runs at wide open throttle. That WOT condition will bypass all the fuel metering stuff.

If the o2 sensor, TPS sensor are sending the wrong info to the computer it can also pull timing way back. With the age of the car I'd check th operation of the TPS first. A multimeter set on the Ohms scale should read the voltage sent to the computer. Read voltage between the blue and black wires. Slowly open the throttle and look for a smooth sweep of the meter.

I believe that this is a good place to start if you want to keep your system stock.

If you want to upgrade then look into the Holley Sniper system. It looks just like a carb and all the sensors and injectors are internal. It also has an internal computer and is self-learning. Very easy to set up. I think you'll need three wires. On hot all the time, one switched 12V wire and a ground. A little creativity should take care of the tranny issue.

^^^ You're refreshing my memory as it use to "click/chatter" even when the Engine was running but not doing that now and I forgot all about listing for it...suppose I became desensitize to the clicking.


Is the solenoid mounted in or outside the Carb (I don't recall). With the key-on should I get 12v from the plug?

I did replace the TPS many years ago when it tossed a "check Engine Light"...not getting any check-engine-light now, which is odd since it's idling so poorley.


I did mention in my top post off idle it runs well, as good as it did before. Emissions/exhaust smell is horrible, not raw gas like it would be 'rich' but/lean, a nasty odor. Giving it a whiff of Starting Fluid smooths out the idle for a few seconds.

And at idle it DOES seem like the timing is being pulled way back...the engine drops RPM and is laboring.
Your posts are sparking my memory...need more info and what to check.


What sucks...I have the ability and have rebuilt Diesel Engines, Race Engines, Differentials, even rebuilt the TC350 in my Vette. I have built Houses, can do Plumbing, Carpentry all the trades except Electrical. but when it comes to 'electronics' especially with a vehicle and diagnosing them I struggle, a lot!
I was about to send my Carb to a local guy that fully rebuilds the computer carbst and tests them on a running Engine ($275.00) but if I have an 'out of Carb' electrical issue that rebuild won't fix anything.


*** need info on what to test, what wires going into the Carb, what color those wires would be etc etc etc (if you have the time to offer such info)
I have the old style Dwell Meter and a Multi Meter.
 

·
Banned
Joined
·
5,331 Posts
Try taking a can of carb cleaner and spray down with the nozzle direct into the primary Qjet Air Bleeds.
They tie intersect direct with the Idle Tubes that go down into the main well where the primary jets are.
Then into the idle down channels.
Should blast dirt and gum out.

I am working today and all week.
And working on Race cars after hours too.
 

·
Premium Member
Joined
·
4,668 Posts
I'll give you some ideas when I get home tonight around midnight. I'm off running drugs now. The solenoid is inside. You just have to remove the top of the carb. Your background is a lot like mine except that I'm also a retired Electrical Engineer. I'll post back in about 5 hours. Knee problems really suck. I've got two of the Six Million Dollar Man titanium hips. Good as new and so will you.

Sent from my SM-G935V using Tapatalk
 

·
Registered
Joined
·
266 Posts
Discussion Starter #15
Try taking a can of carb cleaner and spray down with the nozzle direct into the primary Qjet Air Bleeds.
They tie intersect direct with the Idle Tubes that go down into the main well where the primary jets are.
Then into the idle down channels.
Should blast dirt and gum out.

I am working today and all week.
And working on Race cars after hours too.
Thanks, I'll try that tomorrow...'if' the Jets/Metering Rods are gummy would that stop the solenoid from chattering?
What's odd, this problem came on rather quickly and maybe a coincidence shortly after I filled the tank with Gas.
 

·
Registered
Joined
·
266 Posts
Discussion Starter #16
Sucks, I can't locate all my info, notes, diagrams, instructions etc I used when I rebuilt my Q-Jet a long time ago...and I know I had them.:bang
 

·
Premium Member
Joined
·
4,668 Posts
I replied to your PM and you have some things to try. If we get it fixed I'll drive 8 hours for a good cheesesteak and a beer. Are you buying?:laughing:
 

·
DC PIT CREW BOSS
Joined
·
39,440 Posts
I'll only drive 6 hours for a good cheesesteak and a beer. For 8 hours it better be a steak and scotch:D
 
  • Like
Reactions: hamerDown

·
Banned
Joined
·
5,331 Posts



The Two Very Best Books you can buy on Rochestor Carburetors.


I read both front to back years ago.
Doug Roe is my favorite.
Doug was the original Quadrajet Engineer.
Doug Roe died so he is hard to get a hold of .


Cliff Ruggles is very Good.
Has his own Website.
He is A Pontiac Guy just like me so most may write off & dismiss here.
He is also a Die hard Drag Racer with a Pontiac Ventura with a 455 Ponch all motor that runs 10's 1/4 mile.
You can find him nightly on Max Performance Pontiac forum.
We had lots of fun together talking about Street Racing Live.
Drag Racing in Detroit Michigan & Illinois.
He is a Great Guy.
 
1 - 20 of 51 Posts
Top