Mazda RX-7 1985 carb adjustment


Old 10-26-09, 06:52 AM
Thread Starter
Join Date: Jan 2003
Location: MARYLAND
Posts: 167
Mazda RX-7 1985 carb adjustment

I have a 1985 Mazda RX-7, 12a motor, 5 spd tran. How do I adjust the carb and how do I set the correct idle speed? Also, I get a loud backfire when I decelerate fast (Letting off gas all of a sudden after acceleration). Thanks
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Old 10-28-09, 11:40 PM
Join Date: Jul 2002
Location: Staten Island, New York
Posts: 182
You didn't say how many miles are on this 24 year old, rotary engine. Or condition of ignition system, spark plugs, etc.
When you get a backfire on deceleration after revving, on most engines it could be for one or more reasons - timing chain (I think this engine doesn't use a chain), a bad valve or unburnt fuel getting into the hot exhaust pipe because the carb could be dumping gas & a few other things. But on this 12A, 1.1 liter carburated Rotary engine it could be worn apex seals, specially if miles are high and carb adjustment isn't going to help.

What you should do is try to find a shop that has experience with rotary engines or do an online search for a rotary engine group that might give you some advice or recommend a rotary mechanic. Keep us posted.

Last edited by grandspan; 10-29-09 at 12:08 AM.
Old 10-29-09, 05:54 AM
Thread Starter
Join Date: Jan 2003
Location: MARYLAND
Posts: 167
The car has about 225,000 miles on it. It was last tuned up about 20,000 miles ago (which since I don't drive it much was about 8 years ago). A tune up (plugs, wires, cap rotor) is next on the list of things to do but I was hoping to adjust the idle/carb at the same time as the tune up. I did take your advice and kept seraching and found a great site with FREE pdf versions of the shop manuals for various years of RX-7's. For anyone else who needs them, here is the website: - Mazda RX-7 Manuals

I'm still going through the manuals about the carb, but if anyone has the down'n'dirty quick instructions about setting the idle and adjusting the carb I'd still appreciate it. thanks
Old 10-31-09, 05:50 AM
Join Date: Aug 2009
Location: Tennessee
Posts: 115
Having had several RX-7s, backfiring is a nature of the beast thing with these cars, although it should be more of a pop-pop, not loud. Likely carb adjustments would help, but you probably have some exhaust issues (leak) as well. I'd refer you to a great website with gurus galore, Got to the 1st generation section and do a search on backfiring. I'm sure you'll find what you need.

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