My 86 (specs in sig) has been losing power on the highway at like 45mph. It will slow down to about 30 and struggle to maintaine that. Now since i have a manual choke i was able to close the choke completely and it was able to go alot faster. I switched tanks and no change. Now since it ran better with the choke door closed im thinking its a fuel problem. Just wanna know what to check. No change when i switched tanks so its either the fuel filter or the mechanical pump right? Any suggestions?