first of all, i have an 85 F-250 4x4 with an inline 6 1barrel non-feedback carb, everything is pretty much stock and nothing has been changed or added.

every time i start up my truck in the morning it runs great for the first few minutes, then starts chugging and dieing for the next 15 minutes. ive adjusted everything that can be adjusted and nothing seems to fix this problem. once it gets over this phase it runs great for the rest of the day. two things ive noticed are that the engine seems to be starveing for air and i can hear a loud hissing noise come on every now and then, when the loud hissing noise happens it runs good. another thing is i think i am seeing very small white floaty things in the oil (wich i would guess is a leaking head gasket). the things in the oil are hardly noticeable and it could just be something that was stuck on the dip stick. im pretty sure the problem is carb related. i am about 95% sure the probem isnt the choke or idle mixture. im not loseing any water from the rad and i am burning a very small ammount of oil (exhaust is clear) also theres a crack in the intake/exhaust manifold right below the carb where the two seem to be connected, exhaust is spewing out of that crack. ive sealed the crack before with muffler cement but it didnt really change the way the engine ran and it didnt last very long either. i guess the problem could be alot of things, but like i said, it runs great after the 15 minute warm up. so i hope that narrows it down a bit, any help would be greatly appreciated.