Fuel question or carb size question or maybe something more

[rak1585]

I had a 305 in my truck that was completely stock with an edelbrock 1406 600cfm carb. It had and exhaust leak but ran good with no problems. I redid the top end with stock ported heads, edelbrock performer intake, new plugs and wires (86 stlye HEI Dist), mid length headers and glasspack that dump at the crossmember. I reused the same carb. It was running and driving fine just like this all summer but only around the block a few times to keep it going since its too loud to run on the street since it still needs inspection since its a 1986. Now I try to run it and drive it and it stalls out. In idle it runs fine but at about 1500 rpm it starts to break up and sound bad. Is this a carb problem, another fuel problem, or something else? Can the colder weather make that big of a difference even though I warm it up for 10 mins? Is this just a problem because of the lack of back pressure? I tried playing with the timing a few degrees each way with no changes in this problem. It has fresh gas. I also dont know how many miles are on the engine or carb. Any help or anything is apreciated. Thanks.

[adamsvega]

check for loose valves ,spray out the air bleeds and check the plug wires .it is something either under load that is breaking down ,off idle cuircut in carb or valve adjustment/cam something wore out .