I have an 86 n/a with 125,000 miles. Sometimes when I got to start up my car it just won't catch. And a friend told me to take out a fuse it's like the second in from the left looking at the engine. Crank it for about 10 secs replace the fuse and try again. And then it starts up everytime. But I wanna know what the deal is. Another thing is most of the time on start up sometimes it runs rpms low and when I'm giving gas won't rev up for a sec or two. And when it does rev up it sounds choppy like it's not a smooth rev and sometimes smokes out the exhaust. My thought was something with spark plugs? But my exhaust is also cut off on the pipes at the back axles so I have no mufflers or tips obviously. So idk any help on what's happening or what I should fix would be great. Thanks ahead of time for any help.

 

I cannot remember what that fuse does but I do know why he told you to pull it and then crank the engine for about ten seconds.

You have flooded the engine. It happens when you start the car and then turn it off before the engine reaches normal operating temperature. Rotary Performance.com has a write up about de-flooding and how to prevent it in the future.
Lots of smoke is a symptom of flooding, and is the residual fuel and oil in the exhaust burning off.

A hesitation in the low RPM range like you said is usually called bogging down. It could be a multitude of things. Clogged fuel injector, spark plug fouled, or something else. Try an Oil change to start with, oil can become heavily fuel contaminated from frequent flooding. Read the write up I mentioned. Then you can address the hesitation issue. You may want to look into a Sea Foam flush for the injectors and intake. Change spark plugs and wires. And check your Throttle Positioning Sensor (TPS). If you don't have a Hanes manual for you car, get one. You will be able to diagnose most of your problems from that. You can also find a lot of manuals here.

https://www.rx7club.com/1st-generation-specific-1979-1985-18/download-copy-your-year-fsm-click-thread-get-link-874699/

They have tons of Rx-7 manuals on this page. Be sure you Adobe Acrobat Reader.