My 69 GTX with the stock AVS has had problems starting it's whole life. The new gas makes everything worse as it evaporates quickly, even sitting at a cruise night for a few hours. While you could have some other issues as others have said this is the starting procedure recommend by the outfit (Pony Carburators) that restored the Carter AVS. Run the starter without pushing down the gas pedel for 10-15 seconds to get gas into the carb. Set the choke. Now the next step you change depending on how long the engine's been off. For my car pumping it 4 times was perfect after letting it sit all winter. Pump once for a couple days, don't pump at all for the day before etc. You have have to play with this. Since using this procedure It's never failed to start. I hope this helps. Maybe Rocky can weigh in on this too.