I bought this 1996 StingRay 586 with a cracked block, put new engine in it, only things left old were the ignition system, manifolds and carburetor. This is what happens: It will run perfect for 15 - 20 minutes, then it will start hunting, rpms will fluctuate from 2700 to 3200, like its running out of fuel, it has a new fuel pump, and carb has been disassembled and cleaned and assembled with new everything in it, all the adjustments were done as the Clymer manual specifies. I have removed de anti syphon valve from fuel tank and made sure the pick up tube was clean. Is there any possible way that this could be an ignition problem?