Engine Problem

I have a '74 C-10, and today, it started acting funny, at frist i thought it was the transmission slipping, but after it did it a few times i realized it was the engine. It seems to bogg down a bit, then catch, and it backfires through the carb. I changed the sparkplugs, cleaned the carb..neither helped. Any suggestoins?

check the timing........if the engine has alot of miles on it its possable that it could have jumped timing.

To check you timing chain backlash, turn the crank CW to the "0" mark. remove your cap from the distributor. Watching the rotor button, turn the crank CCW. As soon as the rotor moves STOP! look at your timing marks. If you travels ed more than 4 degrees, replace the timing gears and chain. Also, how did you clean your carb? ie. just spraying cleaner down the throat of the carb does NOTHING for the carb except clean the throat out. Problem could be in the internals, metering portion.