Back fire

I recently picked up a 1966 f-100, it has a built 410 in it but it has been sitting for about 10 years. When I went to start it up the fuel lines were cloged from rust and I fixed that. But now it has flames comming out the carb, not really a violent back fire, it also only runs when the starter is helping it, and it sounds way to quet for it being strait piped. I think it is just the carb needing a rebuild but could it be something worse like out of time cam or bad valve springs. According to the last owner it was professionly rebuilt, then it was driven for 5 years and then sat, it ran when parked but thats it, he didn't cover it, stablize the fuel or any thing else like that.

Only things that will make fire come out of the carb is sticky or burnt valves, or the timing is way too advanced. If there was rust in the fuel lines, I bet it is in the carb too....

So what I have to tear down the heads or can I unstick the valves as is? I would guess it's not timing baised on it was running and then sat. And I am already planning on rebuilding the carb so I'll fing out how rusty it is. Luckly when I pulled it off there was no rust on the inside of the intake.

so what you do is run a compresion test on all cyl that will tell you if you have a stuck valves it could have jump time or it could be as easy as pulling the valve cover off and see witch one is stuck and give it a hit with a mallet or i would pull the heads and get them rebuilt