Well last week on the way home from school the blazer started to act like it was mis-firing badly and/or starving for fuel...i limped it home and replaced my timing chain thinking that it had just slipped a tooth (my distributor was turned quite aways from where it usually was). After installing the chain, i timed it correctly and it still ran the same. So then i checked the fuel pump and it still pumped stronly. I was lost so i took the fuel filter out for ****s and giggles and it was clogged so i replaced it. All was good for about 4 days and it is doing the same thing again. Today i replaced the fuel filter again and took the carb off and cleaned it, to no prevail. So what could this be>? Its a SB400 and the carb is a 4 barrel q-jet.