Thanks for the replies to other post.
I did post this on another forum but so far no responces.

My '80 Vette has a 350 with a competition cams fast road cam. It has no vacuum advance on the distributor ( vacuum goes to a module mounted on the bulkhead/firewall) also it has the std Qjet carb with several wiring connections to it. It runs roughly on idle.
To improve things, I have already junked the AIR pump and hot air feeds to the air filter and disabled the EGR. This has improved things no end. I have an earlier Qjet without these wiring attatchments fitted, and an earlier HEI distributor with the std vacuum advance.

What difference will these make if I fitted them, and what do the wires do?? Must be some kind of emissions stuff?
Ultimatly I want to fit some performance heads and manifold maybe during the winter. Any recomendations??
Thanks again for your welcoming messages. As soon as I get time I will post some pictures.

 

The wires going to your Rochester carb are for an electronic feedback carburetion system. You need this in some states for emissions visual inspection, but no problem disconnecting if you want to run a fully mechanical carb. Just don't let the smog police see.

If you don't have a vacuum advance distributor, then it uses just the weights. You have less advance with this type of distributor, but you can improve things a lot by going to the parts store and buying an Accel distributor advance kit. If you want more advance at lower, more useable rpm's, try lighter springs on the weights. Your 1980 350 will like that.
While you're at it, if it's still running points, try upgrading to a Pertronix electronic ignition system. But follow the instructions precisely.

When you're ready to upgrade, I'd recommend the Edelbrock Performer RPM intake. Get the air gap version if it'll fit. The carb will have to be a square bore Holley, or Demon. I'd say a 600 to 625 DP if it's a manual tranny, and a 650 to 750 vacuum secondary if it's an automatic. Probably the 650. Better torque.
There are several really good heads in the aftermarket, but if you want a very excellent and very inexpensive set up, get the GM Vortec iron heads and Vortec aluminum dual plane intake. You have to get the intake because the ports are a little different from traditional. But excellent performance for very little money. While you've got it all apart, treat yourself to a good set of headers. Flowtech, Hedmann torque step, or Tri-Y headers would be probably the best. You're probably looking at about $1500 for all that.
Look for an increase in compression too. A steel shim head gasket will raise you about half a point. The 64 cc Vortec combustion chambers will also raise you, but stay with regular 0.041" head gaskets for a pump gas friendly 9.5:1 compression ratio. (You'd get about 9:1 with stock heads and steel shim head gaskets...but won't flow nearly as well as the Vortec system).

You might be able to use the spread bore carbs on the Vortec intakes. Such as Edelbrock or Carter AFB. But ask when you call the Chevy dealer parts dept. Those are probably better for the street, even though Holley/Demon gets my preference for top end horsepower.

Good luck. Let us know what you do.

 

Thanks for that.
Smog police not an issue in UK. I already have some (unknown make) headers fitted. How would you rate the performer RPM inlet & heads against Vortec setup? Would the air gap fit under standard bonnet (hood??) ?The distributor is HEI And I think it might take its vacuum advance from this module on the bulkhead. Does this sound right? BTW 4 spd manual.