Chevy 350 engine with HEI runs spark plug gap at 025 will run 035 but starts breaking up when hot very rough 045 What part of the ingnition system is faulty?

The most likely cause of this issue is a weak spark. This could be due to a faulty ignition coil, spark plug wires, or distributor cap and rotor. It is also possible that the HEI module is faulty. To troubleshoot this issue, you should start by checking the spark plugs and wires. Make sure that the spark plugs are gapped correctly and that the wires are in good condition. If the spark plugs and wires are good, then you should check the ignition coil. To do this, you can use a multimeter to measure the resistance of the coil. The resistance should be within the specifications listed in your vehicle's repair manual. If the ignition coil is faulty, then you will need to replace it. If the ignition coil is good, then you should check the distributor cap and rotor. Make sure that the cap and rotor are clean and free of damage. If the cap and rotor are faulty, then you will need to replace them. If the cap and rotor are good, then you should check the HEI module. To do this, you can use a multimeter to measure the voltage at the HEI module. The voltage should be within the specifications listed in your vehicle's repair manual. If the HEI module is faulty, then you will need to replace it.