Running poorly timing or carb or vacume leak

"my 78 cobalt is equipped with

"my 78 cobalt is equipped with a 5.8L (351W) ford small block. it equipped with a holly 4 barrel marine carb. this winter i rebuilt the engine using all of the stock parts except the cam and intake. he new cam and intake are edlbrock "performer". the engine runs pretty good, except for a few things. in order to get the engine to idle, i have to make turn the thing on the side of the carb that controls the fuel mixture / choke to extremely rich, and even then it wont idle below 800rpm. almost to the point where the choke is constantly on unless at WOT. the second problem i have is when the engine is cold, i get A LOT of backfiring through the carb when i try to give it gas. When it is warm, i still get quite a bit of backfiring, but not as bad. if i am at about 1500rpms, and punch it, it runs like a champ. no backfiring, no hesitation, no nothing. it is just below 1500, it runs like crap. i am wondering if my timing isn't off by a little because if the cam and intake. does anyone know what a mild cam like a performer will do the timing specs on a ford small block? any advise you guys have to offer would be nice. thanks."

Vacuum leak is a good possibil

Vacuum leak is a good possibility. Are you sure you plugged all the unused ports on the Performer intake? I run the same manifold and there are several ports you have to plug. Seems like theres one at the back of the carb base that would be easy to miss. You can check for leaks by spraying starting fluid around the base of the intake with it running. Engine should speed up if you spray the leaking spot.

"i like the starting fluid ide

"i like the starting fluid idea! i use it all the time with snowmobiles, never thought of using it for boats. as far as the back of the carb base, that can't be because i used an after market spacer."

[b]"i used an after market

"i used an after market spacer"
Good place to look for a leak..

I don't recommend starting fluid for anything but leak hunting......

"me to. i use starting fluid o

"me to. i use starting fluid on the crank seals on snowmobiles. sometimes if you when you blow a drive belt, the pieces can get caught between the primary clutch, and the block taking out the crank seal and causing, you guessed it, a vacuum leak."

can use propane too

can use propane too