85 Mazda RX-7 tune up questions

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Old 05-31-11, 06:11 AM
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85 Mazda RX-7 tune up questions

I have a 1985 Mazda RX-7, 1.1, 12A carb, 5 speed manual. I am trying to tune it up and have some questions - I have a standard tach (that clamps over the #1 spark plug wire) and that reads about 300 rpm more than the car's internal tach. I also have a manual that says there is a special tach for rotary engines - is that true? Is that why the numbers are so different? Should/can I trust the car's tach? Why wouldn't a standard tach work on a rotary engine? Also, I can't get the rpm low enough to set the timing. Timing should be set at 750 rpm but I can't get anywhere near that without the car cutting off. Is there some trick to this? Finally, the manual says that the idle screw is on the left side of the carb near the front. It also says that there are two screws - the idle screw and the mixture screw right under the idle screw - well I only see one screw - the idle screw. Is there any reason why I wouldn't see the mixture screw? Shouldn't I see it? Any suggestions would be greatly appreciated.
 
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Old 05-31-11, 07:50 AM
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Been a few years since I tinkered with one of those, but a great place for you to go is Mazda RX7 | Owners, Parts, Repair, Performance, Mods, Wheels - RX7Club.com. The 1st gen section has all the info you'll need, plus tech help from gurus.
 
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Old 05-31-11, 03:40 PM
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While you gather up your stuff, and before you leave, you have to remember you don't have cylinders, only 3 concentric lobes. That is probably why a standard tachometer won't give proper readings. The mixture screw may have a hard cap on it, so it doesn't look like a screw. Let us know what you find out.
 
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Old 05-31-11, 04:37 PM
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If I recall, the mixture screw IS there on those nikki carbs, very hard to see. Also, high RPM on those is indicative of a vacuum leak. Those old hoses get brittle with time. The tach on those cars are typically very reliable, you could go by it I think. Be sure to have good plugs, the ones by NGK for sure.
 
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