I have a 69 fastback with a 302 and c4 auto. i havent driven the car for a while and today i start it up and it idles really rough and when you rev it mildly it makes a "tisst" from the carb. then i go to drive it around the block and it makes the "tisst" noise repeadedly and is really lagging on power. i think it might be a valve problem, i cant go to a place to get it checked out until next weekend so i am asking you guys here. what do you think it is? feel free to ask me more questions about the situation to get more info about the problem.
thanks

 

First things first.

How old is the gas?

 

less than a week

 

Check to make sure you have no disconnected or broken vacuum lines.

 

no nothing is disconnected or broken

 

do you think it could be piston rings?

 

Sounds like a vacuum leak. With it idling spray brake cleaner around the carb vacuum ports, gaskets, intake->head gasket area etc. If the idle changes, you have a vacuum leak and know where it is.

 

67mustang302, I 2nd that!!!

 

Check the points. They may be out now for some reason my old 289 when it had points would stick together if it sit for a month or so.
It would have a arc burned on the points i could file it off and it was good to go after reseting the gap.

 

its been changed from the points.