I have a 70 Charger with a mild freshly rebuilt 383. i cant tell you the specs of the cam but its mild. its 9.5:1 compression with headers an edelbrock performer rpm intake and a 750 street demon. the problem i am having is the thing is a dog off the line. it hesitates and bogs down. and if i get up on the stall then let off the brake and gas it, the rpms drop some and it launches like im launching from an idle. once it gets going its alright but i feel like something isnt right i know there is more potential in this motor. also i can never get this thing to break traction ever. ive checked the timing and its at 12 btdc w/o the vacuum advance. could it be the carb? to little or to much fuel?
thanks for the input

 

I would check manifold vacuum at idle and under load, then pull some plugs and check colour.

 

What are the cam specs ? What rear gear does it have ? Secondaries opening too soon !! Idle vacuum ?

 

Just because the cam is mild does not mean it's installed correctly. WHY don't you know? You buy this used? Cam "degree" can make a tremendous difference in low end torque and "on the www" there's been quite a bit of talk on cam drives or cams that don't seem to be ground in a way that you can trust non--adjustable drive setups

12BTC is probably OK for a starting point, but even my mild cam 318 "about the same" as a 340 cam runs 15--17 initial timing

Any chance the mechanical advance is stuck?

Are you certain that all 8 are firing, IE does it idle smooth?

Other than that...........carb................

Idle adjustment?

Accelerator pump shot?

Power valve?

Jetting?

Way WAY too many variables here

 

Add More Accelerator pump shot....
And tighten up the secondary upper air plate....

That should help it out....

Just my 2 cents.... Keep us posted...

 

I've got a 69 charger that has/had the same type issues. I'm in the process of getting things buttoned back up and fired up. It has been one thing to fix after another. Once I dove in, it was like a tail chasing experience. Same issues as you described but add low vacuum to the list.

Things I have found to be wrong so far...

Valve seats off leaving intake valves sticking open
Rockers off with wrong length pushrods. (Yeah that's a good one)
Heads and top of block been shaved down so the intake didn't fit/ seal properly
Timing way off.

May I suggest a 650 cfm carb if you can get your hands on 1 to try.. Most everyone I have spoken to said 750 will work but not as good as 650???

I haven't gone there yet..

I'll let you know how things go when I fire it up.. But in the mean time, buy stock in these guys! They are a huge help!

Good luck!

 

If like to add to what these guys said;
Compression check, ASAP