I have a 1986 Iroc with lg4 and Rochester quadrajet. I want to change filter in carb. How do I know if it is a long or short filter without taking it out?

 

If you can see the carburetor number on the main body of it or along the baseplate, it will read something like 17089234, take that number with you to the parts store and have them cross-reference that to your year of car and size of engine to be sure it's the original carb, motor, etc. That way their regular computer catalog listing should tell them to hand you the right one the first time.