Hey gurus,

Need some advice here. 81 veto (all factory and matching numbers) is in the shop. Mechanic says carb needs to be rebuilt. It's already been rebuilt about 5 years ago. He's recommending to replace the carb....so...what should I do?

1. Order a rebuilt factory quad jet and bolt it up myself? I have good tools and a garage. Is putting on a new carb tricky?
2. Get a brand new carb from one of the corvette websites like Ecklers and do bolts that up myself.
3. Or do one of these....
What say you?

 

None of the above

Prime option:
Send to CF member Lars

 

That's an ECM-controlled carb, so I can't assist with that one. If it's the original carb, be very leery of replacing it with e "rebuilt" POS. There are no "brand new" Q-Jet ECM carbs available from any source - the commercially "rebuilt" carbs from the Vette suppliers are complete junk.

Lars

 

How about going into some detail as to exactly what the problem is that makes your mechanic think it is the carburetor?

 

Well ... in this ECM Qjet matter, seems Lars is not an option.

Seems OP Jantonb resides in South Carolina ... I do too and KNOW there is no smog check / inspection in our fair state.

Unless this '81 is a collector car, I suggest removing and conserving Both OE Carb & OE Distributor.

Several truly NEW carb options. Holley and Carter/Edelbrock. I suggest a Non ECM QuadraJet. Perhaps Lars could assist with that.

Suggest a NEW 4-pin HEI Distributor (like found in '75-'80 C3). Those can be had for $50 -$500.

 

I had suspicions myself...not a mechanic...but know the car well and have good tools and a place. However, felt it was a little above my pay grade, that why I sent it to him. Symptoms: Won't hold Idle, except when it has sat over night when warming up. Once warm and driven...wants to idle very low or none at all. Then....just won't run on its own...will start every time...but with out feathering the gas...will die.

 

I suspect easy way would be to replace it with an older model QJ. see what lars can sell you. Other then that if you want a new carb new street demon would be easy install. the edlbrock carb is a square flange and different bolt pattern carb. The street demon carb will bolt right on your manifold and has same good small primaries as the QJ used. Holley still makes a QJ replacement carb but its not strictly a hook your fuel line up and go thing either. Plus its a 50 year old holley design has poor adjustabilty to it. Im thinking best overall thing you could do buy the smaller 625 cfm street demon for your stock car. Its same price range as edlbrock carb fits your manifold and if you look at its design far better then what edelbrock has to offer you or holley.

 

Sounds like the Q-jet works fine when warming up, but not after warm-up. That would indicate a problem with closed-loop operation (normal operation as an integrated system: ECM, O2 sensor, etc, etc. all working together). In 'open loop' mode (during warm-up), the ECM operates to a fixed set of instructions to set fuel mixture and timing.

I suspect that your problem is likely a defective sensor (O2, temp, TPS, etc.). If the carb were not working properly, it wouldn't work OK in open-loop or closed-loop mode.

That ECM is per OBD-I format. There is a process to download any trouble codes from the computer which would help you diagnose what is really wrong with the system. Google up the info on your '81 system to find the trouble code listing and also the method for 'reading' any captured trouble codes. An important question is if your Check-Engine Light is working or not. When you turn the ignition key to "ON" position (not RUN position), the CEL should light. When engine is started, the CEL should go OFF. If that works as intended, you can easily off-load the trouble codes and get a 'heads-up' on your REAL problem.

P.S. There is nothing "wrong" with the basic ECM and engine operating system on the '81 C3. If the components are working and the system is operational, it should work much BETTER than a C3 with a standard carb. I wouldn't dump your system without first finding out what is actually wrong with it.