Hello all I have a 1986 firebird previously had a carbureted 305 in it. It got swapped to a sbc350 from previous owner. 350 is freshly rebuilt with a fresh quadrajet carb HEI distributor. The car starts up fine and runs great and after warm up idle hangs out around 1000rpm. But after about 30 minutes of running/driving it dies. I was driving around town and it just died after about 30 minutes it would crank but no start but if I let it sit awhile it would fire up like nothing happened. I then tried to replicate the problem at home and I let it idle for 30 minutes and then I noticed the rpm started to drop by about 100rpm then a few minutes later would drop again until it got to about 500 and then it of coarse was struggling to run until it died and then same thing would crank but no start and I would let it sit for 1 hour and it fired up again like nothing happened. coolant temp hangs around 180-190 also.

any advice on where to start to diagnose the issue is appreciated or if you guys have had a similar issue to this and how you fixed it.

thank you!

 

Run til it dies and won't restart. Then check to see which is missing, fuel or spark.