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81 carb and computer

corvette66

Well-known member
Joined
Nov 3, 2003
Messages
519
Location
Mattawan MI
Corvette
1969 427
I just got an 81 with no motor, i started looking over the engine bay, and i noticed it has a return fuel return line. What type of carb was on this car? Did it really have a return line? I was also wondering what all the computer in this car controlled. I am going to put in a MSD amp and distributor, is there any unusual things about these vette computers that i should know about before i instal the box?

I am also going to put in a standard trani, there is nothing different about the firewall from a automatic to a stick is there, i should be able to bolt the clutch pedel and cylinder right to the wall right?


thanx
 
Joined
Apr 29, 2001
Messages
2,141
Location
Rio Rancho, NM
Corvette
1981 HD Suspension; ZN1 Option
I just got an 81 with no motor, i started looking over the engine bay, and i noticed it has a return fuel return line. What type of carb was on this car? Did it really have a return line? I was also wondering what all the computer in this car controlled. I am going to put in a MSD amp and distributor, is there any unusual things about these vette computers that i should know about before i instal the box?

I am also going to put in a standard trani, there is nothing different about the firewall from a automatic to a stick is there, i should be able to bolt the clutch pedel and cylinder right to the wall right?


thanx

The L81 came with the Rochester Q-Jet E4ME. This is the computer controlled carb.

Off the top of my head; TCC lock-up, emission controls, timing advance, and fuel-air mixture. Maybe I missed one, but I believe that there are 4 main functions.

But to make it work without the computer giving you codes, most everything monitored needs to be hooked-up and functioning.

The MSD ignition you are referring to will do away with the stock distributor. Just disconnect the engine harness at the fire wall, and tuck away. I believe that the computer will still "tell" the TCC solenoid when to lock-up. The speedo has a sensor also used for the TCC, so if you go for one of those 140MPH/160MPH speedos, then make sure it includes the sensor window. The last dis-connected engine I ran in my L81 worked fine, and every once in a rare while the check engine light would eliminate, but i never did discerned a pattern as to what could have been causing that.

Other than that, it's pretty much like the earlier C3 vettes. The California version for the 1980 model year is pretty similar to the 1981 features.

GerryLP:cool

p.s. oh yeah! The return line is for the fuel pump.
 

corvette66

Well-known member
Joined
Nov 3, 2003
Messages
519
Location
Mattawan MI
Corvette
1969 427
thanx for the info,


About the return line...... If this car had a quadra junk carb, it would not have had an in-tank fuel pump that is needed for the fuel injected or cross fire 82 and 84's. it would have had the mechanical pump on the block like all other carbureted engines right? That being said i still don't understand the reason for a return line to the tank, or as you mentioned "the return line goes to the pump" why does the return line go to the fuel pump? I have only ever seen fuel pumps take fuel from the tank and suply the carb with one line. The 81 didn't have an in-tank fuel pump did it?
 

Peer81

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May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
An 81 has a pump to the engine that's correct, an in-tank fuel pump started with the TBI's in 82. Why the return hose is there I'm not sure, I always thought it was for the fuel to circulate when the engine's doesn't need all the fuel. And IMHO a Quadrajet that has been tuned well is far superior to the other "dead simple" carbs. It just takes some effort to understand. :)

Groeten Peter.
 
Joined
Apr 29, 2001
Messages
2,141
Location
Rio Rancho, NM
Corvette
1981 HD Suspension; ZN1 Option
...About the return line...... i still don't understand the reason for a return line to the tank, or as you mentioned "the return line goes to the pump" why does the return line go to the fuel pump? ... The 81 didn't have an in-tank fuel pump did it?

I suspect an anti-vapor-lock feature, but I would have to research that. The fuel pump has an inlet, outlet, and fuel return ports. The 81 had no in-tank fuel pump. Like Peer81 said, the 82's were the first ones with the in-tank fuel pump. I understand that the 82's fuel tank fits right into the 81 C3's..

GerryLP:cool
 

corvette66

Well-known member
Joined
Nov 3, 2003
Messages
519
Location
Mattawan MI
Corvette
1969 427
hey thanx for the help guys
I guess they do have some sort of return line, not a real problem, i just wanted to know if i had to drop the fuel tank to remove an electric pump. Glad i don't have to :)
 

Peer81

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Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
As a bonus, on the other side of the chassis there is another fuel line returning to the fueltank, from the charcoal (Evap) canister. :)

Groeten Peter.
 
G

George

Guest
Hi All,
I recently replaced the original fuel pump on my '81 which had a return line back to the fuel pump. The new pump is a high flow Holley which doesn't have a return line. I then started to have surging and misfire problems from take up. We have now put a fuel filter after the pump and before my Holley 650 double pumper carby. The fuel filter has a return line which I have now reconnected. My problems seem to have stopped but I am still trialling it. I have therefore ordered a fuel filter from the early '69/'69 models which had the return line also.
Hope this helps.
George.
 

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