I have a '92 F-350 460 and on really hot days like 95 + when i try to start it cranks for about 3-5 seconds then when it starts it idles really rough, also throws black smoke out tail pipe. If i give a little throttle it goes away after a few seconds. Any thoughts would be appreciated. Really embarassing when people see. On normal temp days again 90ish and below starts right up no problem.