backfiring from both ends!

[tcb1969]

I have a bone stock 352. Recently put a rebuilt 2bbl carb and completely new exhaust system on. The truck runs better than ever - but I have started having minor backfires. The truck doesn't backfire on deccelaration so I don't think the exhaust is contributing to it. It backfires out of the carb occasionally when starting the engine. Then when shifting (it is a 3 on the tree) it will backfire in the exhaust manifold. It doesn't pop loud out the tailpipe - sort of a deep, muffled "pfffft" from under the truck.

I'm guessing there is a bad gasket or seal somewhere inside the carb - like a bad power valve. Before I start taking anything apart I was hoping to get some opinions.
John

[Faithful Old Road Dog]

Backfire out the carb usually means too lean on the mixture. Also check your ignition timing.

[willowbilly3]

Also a previously un noticed light backfire on deceleration can mean that the points are going closed. This is very common with the points available today. The rubbing blocks are soft and in the first 500 miles the block wears in and you loose point gap.