1987 Mazda B2600 4X4, 203000 miles, 2.6l

I was losing power in 4th gear at around 2500 rpms so I changed the fuel filter, spark plugs, air filter and cleaned the carborator since none of that had been done for quite a while. Now I can't get the truck started. I made sure that I put the fuel filter on in the right direction and the arrow points in the direction that the gas flows from tank to engine. It started fine before all these changes, now I can't get it started at all. What did I do wrong? I'm thinking that I put the plug wires on wrong, but I've switched them around and it still won't start. Let me know.