Starter

ok i have a 92 ford mustang light mods, heads intake manifold and exhaust. i have an 91 or older style starter in the car, and when i start the car the starter stays engaged. so im not sure if this has anything to do w it or not. Ive tried everything else i replaced the selonoid 2 times, took the starter off and had it tested and it was good! I also changed the ignition switch! so any input would b greatly appreciated!!