Need help with exhaust backfire

[yellowblazer1969]

When i crank the blazer it runs fine but whan i try to drive it and accelerate it backfires out of the exhaust. I am not sure if it is doing it out of both sides of the exhaust. I understand that usually exhaust backfires mean too much fuel is being delivered and it is igniting in in the exhaust. Can anyone tell me what to adjust on the carb, is it the screws or the return spring. Could this be caused by anything else?

Thanks, chris