Why is it that being to rich is only a problem when you own a car?

I recently picked up a stock 87 NA that seems down on power compared to my previous 86. It is backfiring at high loads on the engine after letting off the throttle for shifts. Replaced the plugs last night and they where pitch black (pictures soon).

I'm new to rotaries and really don't even know where to start to try to diagnose this.

Some things I think it may be are non working 5th and 6th ports or previous owner upgrading the fuel pump. What else could be causing this that I should look into?

 

Check the aux ports first, it's fairly simple. If they're stuck closed, they'll cause those symptoms. First thing I'd check.

It could also be a fuel issue where your fuel pressure is too high and you're running wicked rich.

Or it could be one of a number of other issues. Like an out of adjustment TPS, an out of adjustment dashpot, or a stuck injector.

 

The dashpot has nothing to do with fuel amount, nor is it even used for fuel or emmisions. Its used to slowly shut the thorttle plates instead of allowing them to snap shut.

Rotaries run rich in general so there may not be much you can do besides doing a complete tune up and possibly adding a fuel managment computer of some type.

I would get your injectors cleaned, check the TPS (which doesn't have a big effect on fuel load during acceleration), AFM, fuel pressure regulator, compression and AUX ports.

 

Dashpot could cause abhorrent backfiring at throttle close. If the rich condition is fixed and it still backfires, this could be the cause.

Both conditions could be related, or they may be independent, I'm shooting for the latter, because it doesn't hurt to check components and run maintenance.

 

Never had an issue with this in the 7 years of owning my car and the 2 engines that have been in it. The ECU cuts fuel when the throttle is shut so it won't backfire. I have even had the TPS unplugged which means it injects fuel during decel and without the dashpot, I still got no backfires