Carb and tuning issues with new headers

[smrcuda]

My 68 cuda has a 340 with a mild cam, automatic trans and 355 read end. I just put a set of TCI headers on it with a new cross over back to the mufflers. I had headers before with no cross over. Car ran great. I had to run a lot of advance because of cam (I don’t know the size of the cam) and it did run a bit rich. I drive it on the street so it's a cruiser not a racer.
Since installing new headers and crossover I seem to be having some problems getting it to run smoothly. I have to also think the problem may be caused by the new exhaust system which is more efficient now. I'm sure it is in 1460 Edelbrock Carb and the timing. I have noticed the primary discharge nozzle has fuel coming out at idle. I'm sure that is causing the rough idle. Not to mention the back fire at idle and loading up.
I have purchased to tuning kit for the carb and have started working with the springs for the meetering rods. The edelbrock manual says to go with spring that has lower vacuum, but the says might have to go the other way.
I sure this is not a unique problem. I'm sure some of you have run into this. I haven't.
I sure would appreciate any ideas or direction.

Thanks
Steve

 

[Dart-swinger]

Whats your timing reading at idle with the vacuum advance hooked up?

My modified 340 runs best when it's reading 10btdc at around 800 idle and advance all in by 35btdc by 2000rpm .Setting the mixture screws with the car in gear with someone in the car and holding the brakes helps too

 

[redfastback]

My 68 cuda has a 340 with a mild cam, automatic trans and 355 read end

[/QUOTE]I had to run a lot of advance because of cam (I don’t know the size of the cam)

how much is alot of advance? what is total, and what rpm is that at?

i like the first metering rod change they say, #23?? what is the vacuum reading at idle?

 

[smrcuda]

Vaccum is at 5 to 6hg at Idle . Not sure where timing is at. Timing light broke. I set it advanced enough so it will turn over easily.
I'm going to have to invet in a new timing light. It also has 3000 stall converter.

 

[dgc333]

5 degrees is not nearly enough intial timing for one thing. You need to get the timing set up for your combo before you can worry about getting the carb dialed in.

The amount of intial timing is a function of the cam and how much over lap it has. The more overlap the more timing. Don't be suprised if you need to have the initial timing set to as much as 20 degrees BTDC. My hot 360 is happiest at 15 degrees BTDC with a Comp XE268H cam which has a fairly wide lob spacing that reduces the overlap that a more typical 268/280 advertised duration cam has.

With an idle vacuum of 5-6 "Hg you either need a ton more timing or the cam is very big. You adjust the initial timing by advancing the timing in 1 or 2 degree increments while maintaining the idle rpm until you get max manifold vacuum.

NOTE: if you are much beyond the factory 10 degrees you will need to limit the total mechnical advance in the disributor to around 35 degrees. Stock distributors require welding slots, after market such as the MP distributor have adjustable limits for mechanical.

Also, something is wrong with the carb if you have fuel dribbling out.