I got this 91 fc na thats knocking above 3500 rpm any thoughts

 

secondary injectors.

DO NOT DRIVE until its fixed, you will blow your engine.

pat

 

what exactly does knocking feel like

 

do you know what it might be ?

 

knocking on a NA is caused by two things:

too much timing advance
not enough fuel

since it doesnt knock at low rpm, that probably means that your timing is ok
secondary injectors come on at 3500 rpm. so does your knocking.
which means that your secondary injectors are working poorly or not at all, causing a lean condition, and knocking.

pat

 

thanks Ill check it out