So I just bought a 1979 RX-7 and it idles fine, accelerates great, and the motor is tight, but while cruising the engine starts surging or stutters, why is that happening and how do I fix it, I just had the carb rebuilt, and I think that the primaries aren’t getting enough fuel, but when you step on it it goes fast(lol)
from what I understand it could be my fuel delivery. But what can I do to fix this problem?

 

Other might have a better idea. but check what the flow rate needs to be gallons per minute or hour. unplug the fuel line from carb and check the flow rate via turning on ignition and if the flow rate is enough.

if the flow rate is not what it needs to be look to the fuel pump and fuel filter.

might want to check the tank for rust while you're at it...

 

Sounds like the fuel filter could be slightly clogged. Has it been changed recently?

 

It's your fuel filter / gas tank . Dump a bottle of seafoam in the tank and it will " fix " the issue . I had this issue three days ago and it went away .

 

I suspect old and possibily water in the fuel, when I opened the fuel cap it had tremendous vacuum in the tank. Is the fuel cap supposed to be vented in this car?

 

The gas tank does have an open vent. The vent hose goes into the frame just a small amount. Might try see if it's clogged.

 

Any problems if I drill vent holes in the gas cap?

 

Some pressure is ok. If your soft fuel lines have not been replaced that you know of, replace all of them. I just did this on two 1979 RX-7. Take lots of pics. You will need to support the gas tank and remove the straps to gain access to the top of the tank. Get a three pack set of hose pliers from Harbor Fright. It really helps. I had no idea about hose pliers but they work really well. The fuel lines are 6mm and 8mm. Also replace all the hoses at the fuel pump.

 

just leave it off and take it for a spin before drilling holes.