Anyone have any Idea what this thing is for?
 

It's right behind the Airbox on my 86 and has R <------> L (see picture) I was figuring it means Rich and Lean but it doesn't seem to have any noticeable effect on the way the car drives.

I'd check the manual's for what it is, but I have no idea what it even does.

http://imageshack.us/a/img856/9542/i...1002180656.jpg

its the variable resistor... it lets you play with IDLE fuel mixture to an extent

The car has to be fully warmed up before you would notice any change from changing the screw position. And the FSM suggests jumpering the Initial Set Coupler before making adjustments.

The Factory Service Manuals for all years of RX-7 (and many other rotary cars) can be downloaded for free here: Foxed.ca - Mazda RX-7 Manuals . They contain all common service information information and more, and are an essential tool for any sort of service work that needs to be performed on these cars.

Additionally, the Haynes service manual for the 1986 thru 1991 RX-7 (both turbo and NA) can be found at most local auto parts stores or purchased from any good bookstore (ISBN number 1 56392 007 7). It is only about $25 and is a great quick reference for things like this. Not only does it contain most of the information in the FSM condensed into an easy to read format, but it includes full wiring diagrams as well.

These manuals will answer 99% of service related questions for the car and if you intend to do your own repair work, you will need at least one of them. Preferably both, since the FSM is a free download. The Haynes is a good quick reference covering 99% of questions, while the FSMs show complete and detailed procedures.