poping or back fire!

I have a 76 KZ750 that sat for about two years. When I started it it was poping from the tail pipe. The tank had some rust so I cleand the tank and the carbs. I still have the same prob. I cleand the carbs agan but still runs the same. It starts without a problum but when it hits about 3k it pops alot. also when you let off the gas. Any suggestions.

vacuum leak is most likely.

Mine's doing the same thing. I was thinking that the valves might not be sealing properly on mine? Do you hear it from the carb sometimes too? I was also thinking that I needed to do a major tune up to it. Change the plugs, plug wires, look at the timing and so on. Have you done that already? Notice any differences if so?

Yes I have set the time,changed the points and plugs. I have also spraid carb cleaner around the out side. I think I may try a new set of carb gaskets. It could be a vacume leak. I will try to check the rubber parts better. Thanks