Actually the shutter valve has nothing to do with backfiring. The shutter valve was designed for 2 reasons. 1). To lower emmisions. 2). To improve fuel economy. It is designed to shut off fuel to the rear housing during deacceleration.

The Air control valve is the main culprit that contributes to backfire situations.
Also it is not the shutter valve that gets stuck in place at times, it is the shaft that goes thru the intake manifold.

The backfiring on the 79-80 models was an inherent problem. The Air control valves would fail. Also the Thermal reactor design was a contributing factor with this. The deaccel system on the Sa's also relied on the dashpot function. Without slowing down the throttle to the rest posistion it also contributed to backfiring.
The only real cure I found on the Sa's after repairing and adjusting the control system parts to remove backfiring. I learned to keep the throttle partially engaged during shifts. This meant keeping part throttle while you were shifitng. This kept the throttle from returning to the rest position and eliminated the backfiring.

 

Rx7doctor,

Right,
By the induction of air only by this mechanism during deceleration it will follow there will be lower emissions and add to improved fuel economy too. It also allows for a more complete burn of the left over fuel in the exhaust during this event before the exhaust gets to outside air which addresses the backfire issue.

Seemed like this was Mazda's attempt at adding a second measure to address the backfire issue and at the same time make the feds happy(er).

What do you think?

My minimum recommendation for the SA's: Remove emissions components of your choice, install a good header to tailpipe exhaust, lean out the overly rich carb and monitor exhaust gas temperature -this last part I have not done yet. Mount the original SA exhaust system as an exhibit in your garage.

regards
two79rx7's

 

No.

 

Got a call from the guy doing the carb today. As it turns out, he's got to drill out some stuff in it. It was real bad, I guess.

I believe this would be the answer as to why the car won't work.

 

I was going to post yesterday,

no air leak in base of air cleaner as reported by you = no or unlikely shutter/coasting valve fault to cause your problem.

I noted a few members with nikki carbs for sale, usually inexpensive and fast replacement if the seller says its a unit just removed and worked fine.


two79rx7's

 

Problem is I need it by Saturday morning. :\

 

post WTB nikki carb in 1st gen section parts for sale
see if somebody responds to sell you a good one near where you live for a good price

 

My 79 RX7's Tac pointer would bounce up to 1000 rpm's to 1500 plus and down again in less than a second time interval. The problem was not my wiring, it was the Distributor "Points Plate" that was lifting upwards by a 1/4 inch. Remove the 2 screws holding the plate down, and lube the bearing under it, and the weights also. (My bearing were bad, I did not feel a smooth rotation of the plate after lubeing it)...This lifting of the plate, caused the trailing points rub block to touch the cam prematurly, making the points open too soon. Test this by lifting the plate with your fingers at one end and watch to see if your points open and close. . .This opening made my RPM gauge to be unreadable, and Yes my timing was not the best and it really was the timing issue that led me to shim the plate which gave me a steady timing dwell and consequently a Tac that now reads steady. I shimmed the "Point Plate" with a thicker washer at the hold down screw, to hold it downwards preventing the 1/4 inch upward lifting, but, remember the plate must have a gap under it for the vacuum advances of the Leading & Trailing to move freely. Greg5656

 

4 years, 31 days... not bad!

(& welcome aboard)