Troubleshooting
All this is totally not related to LS1's, ECU programming, etc, BUT....
I dealt with this myself. Carbs in general - especially those designed on older engines - don't always play well with gasohol. They were designed before anyone was adding alcohol to the gasoline available at all the pumps. You can't generally get enough choke to get good fuel evaporation.
My solution at the time? I bypassed the choke, and use the gas pedal to put a couple pump shots in the intake before trying to start and then use the pedal to keep it running until it warms up enough to run steady. Even doing all that, the truck used to get 23-25 mpg. once gasohol took over, it dropped to 17 mpg on a good tank. I had to run premium in it all the time also. Regular 87 was almost a lost cause. if you can find an ethanol free gas station, use it for five consecutive tanks, and you'll find that the truck starts doing much better.
My long term solution? I swapped it to a LS2, and the fuel injection solved the problems. it's now a 400 HP truck getting 22 mpg vs a 100 HP truck getting 17 mpg.
I dealt with this myself. Carbs in general - especially those designed on older engines - don't always play well with gasohol. They were designed before anyone was adding alcohol to the gasoline available at all the pumps. You can't generally get enough choke to get good fuel evaporation.
My solution at the time? I bypassed the choke, and use the gas pedal to put a couple pump shots in the intake before trying to start and then use the pedal to keep it running until it warms up enough to run steady. Even doing all that, the truck used to get 23-25 mpg. once gasohol took over, it dropped to 17 mpg on a good tank. I had to run premium in it all the time also. Regular 87 was almost a lost cause. if you can find an ethanol free gas station, use it for five consecutive tanks, and you'll find that the truck starts doing much better.
My long term solution? I swapped it to a LS2, and the fuel injection solved the problems. it's now a 400 HP truck getting 22 mpg vs a 100 HP truck getting 17 mpg.
Solved ! 
