So i got my 355 built to replace the blown L69 in my 15th anniversary trans am. its a 355 with keith black flat top pistons, 062 vortec heads, summit dual plane intake, comp cam 262 cam, flowtech headers and ypipe. I tried to reuse my stock q-jet from the car but it doesnt want to idle without holding the choke open, then once in a while it will idle but has absolutely no power like it is starving for fuel. Car has been properly timed with the valves adjusted correctly. Just had the carb rebuilt and thoroughly cleaned. So i guess my step is to replace the carb, but not sure what to get. Its a street application, i want to stick with 4 barrel, electric choke, and vacuum secondaries, any suggestions

 

Where is the timing set, and how did you set it?

 

It's set at 6 degrees at idle, used a brand new Matco timing light that has rpm and advancing

 

Timing advance at idle seems way too low. I am not familiar with the stock QJet that came on the L69 or the distributer. However, any small block with a decent cam will need something like 12-14 degrees advance at idle (real low idle so you know the mechanical advance isn't kicking in).

 

My vortec heads took about 14 at idle but 12 is fairly normal. Idle advance is not to important anyway get a friend to rev the car and find out when the distributor stops advancing should be between 2500 and 3000 rpm.

After you find out the max advance RPM adjust the carb idle screw until it idles at that RPM and have a friend turn the distributor while you work the timing light until you get about 34 degrees mechanical advance.

 

I don't agree with this approach...especially if you are using a stock type distributer. By the time you set the full advance to 34 degrees, your idle advance will be too low for any SBC with a non-stock cam. Of course, vacuum advance hooked to a manifold source will cover up a lot of that. I like to get my base where it works best and then modify the distributer to limit total to 36. Then you can play with 2 degrees to either side of that.

 

I never had a problem with my idle advance being to low with any of my sbcs usually running a 262 or 274 cam. Usually when I do this method my advance at idle is around 12-14. How many degrees advance does a stock distributor give? Most I have worked with give 18-22 at full advance usually near the 22 range giving you about 12 base.

 

By "how did you set it", I was wondering if you disconnected the ECM connector from the distributor before setting the timing.

6 degrees BTDC at idle with the ECM disconnected is correct. What you have after reconnecting the ECM is controlled by the ECM, and you aren't going to change that without reprogramming the ECM.

 

Good point I forget he was using a CCC I was just thinking a regular distributor system.

 

I was thinking 1970's HEI. The last one I played with (from a 1975 Nova) gave over 25* mechanical. Recently, I have been using the GM performance HEI. It has a total mechanical of 20 degrees...which makes the base timing nice (as Midias stated above).

I should also say that I was thinking non-CCC here also!

 

Crazy question how did it run before the swap?

 

Yes I disconnected the ECM when setting the timing

 

Did you adjust the idle mixture screws? What are they set at? If they've been turned too far out you're running too rich for start up. I originally had the L69 motor in my T/A and swapped to a 350. I switched to a non-computer controlled carb and distributor. Still with a 750 cfm Rochester, I have the idle mixture screws turned out only 3 turns each. Car starts and idles fine. Too much fuel can make the engine feel like it has no power.

 

This is a Vortec-type intake manifold, right?

Are you saying the choke doesn't open on its own as the engine warms up?

 

Yes it's a vortec intake, the choke would open up but it had to be held almost completely closed to run. The old engine was blown and didn't run so could test carb. I slapped a non cc carb on and it runs great

 

There you go time to rebuild the old system.