I'm having a problem on my 1970, 454ci, 390hp (LS5).  At idle it runs smooth. At high RPM it runs fine.  When I gun it, it backfires sooooooo bad.  Someone suggested that it might be that the vaccum advance is not working.   I have had the carb tuned before and this problem started after that, and has gotten worse and worse.    If you have suggestions please forward.   But for now I am assuming this is a vacuum problem somewhere from the carb to the distributor.   My first thought was that maybe this solenoid was not installed correctly.

Paul,

the tcs sel. job is to allow vac. adv. only in high gear, you have a switch on the trans and when it goes into high gear it electricley opens the sel. to allow your motor to have vac. adv. in high gear, take it clean off the motor you don't need it all it will do  is hurt your performance through your other gears,  save it for if you sell the car for the new owner, retime your motor to factory specs with the "timed vacuum port" capped,  on the carb, after you have set the static initial timing and locked down the distributor reconnect the vac. adv. line from the dist. to the "timed vac. port" on the carb, on the front of the carb you will see three vacuum connections, the big one in the middle is for the pvc valve, you have two smaller ones, one on each side of the pcv conn., one is for "full engine vac". and the other  one for "timed Vacuum" which you connected your distributor too, if you look at the carb closely at the two smaller vac. connections  you will notice that one sits higher than the other,  the one that sits higher is the "timed vac" port, Edelbrock does recommend fuel presser to be no more than 5.5 lbs presser, more than that may cause the fuel inlet valve not to hold causing  flooding,  check to see if you Fuel Reg is adjusted properley......remember when the car is idleing  and you are free winding -"gunning" the motor and getting a backfire your are not getting vac adv. because you are not in high gear, also you cannot just move the distributor and not put  the timing back correctly it won't run right, .....I did not take in cosideration that you might still have the smog pump and the rest of the emmision equiptment in place, do not remove the tcs, do what I suggested but just bypass the tcs and go from the carburator directly to the advance cannister and see what happens, to check if the vac. adv. cannester is working with the rubber hose connected to it blow into the hose, if you can blow into it,  it has a hole in the diaphram and it is no good and has to be replaced,  if you can't blow into it its ok  anips2009-07-15 21:24:52

One thing that I see that is different.  The higher port on the edelbrock is form time advance, but it is for emmission controlled engines.  The lower manifold vacuum is for non-emmission controlled engines.  I have it in the lower manifold vacuum.   

I had my wife put it in 3rd gear.  I felt the same suction on the open port that I do in the other gears (ie I have suction all the time).  I'm thinking the open port is not the one I think it is supposed to be.  Maybe the solenoid is stuck in the energized position.  Check out this picture of the tcs solenoid - http://www.chicagocorvette.net/images/parts/C/3/C3770.jpg