I have an 84 what use to be a gsl with a 13b motor. The carb is a holly 600 and i have a racing beat dual pipe header and exuahst system. The motor is a factory reman with 2000 miles on it with stock ignition. My problem is at 2000, 4000, and 6000 rpm i have a wierd virbration. The vibration happens no matter what speed, gear, or clutch position. Does any one have any ideas on what might be causing this?

 

might not be engine related. Does it only happen when the car is moving, at idle. need more info.

 

If it's RPM related, and you're certain of it, I'd check the fan/water pump. I don't know about the 84's, but I know that if you use a S5 (89-91) fan on a S4 (86-88) waterpump, the shaft of the waterpump is too small for the fan (even though the fan bolts up perfectly), causing it to become off-center and then causing weird vibrations at certain RPMs.

Other than that, I'd check all the (make sure they're tight) belts and look for bent pullies. Also, if your clutch is missing a bolt/dowel, it can cause some weird vibrations.