Keaponlaffen

My car has a pretty bad miss when it's idleing. Is this normal? I have new plugs, the car's timed perfectly, and it runs fine when in the higher revs. The only time it's noticeable is when ithe car is idleing (1000 rpm), and when I step on the gas from idle, or lower RPMs (it pretty much floods if I floor it from idle, even if in Neutral). What is the first thing you guys reccommend doing? Replace the plug wires? (they are a bit old)... maybe the distributor cap? The distributor rotor? Is there a module in the distributor that needs to be replaced? The owner before me put on some kind of electronic ignition, but I don't know what kind, OR how well it was converted...

Help!
Jeff

Pele

iTrader: (28)

I'm thinkin mixture... Set the ignition back up as stock to see if that's the problem though.

Incomplete or improper mods by the DSPO's really tick me off. I am meticulous when it comes to stuff like wiring or holes cut/drilled in the body.

Keaponlaffen

Yeah, DSPO mods are starting to **** me off too. I had to remove all the metal floor pieces under the carpet and trim peice in the trunk of my car becuase it had holes cut in it for subs!? I would set the ignition back up stock, but I don't have the original stuff, and I don't know how it's set up.

How do I correctly set the mixture? I had to crank it down becuase it was running so rich it wouldn't idle at all, even with the idle set screw set as high as it goes...

Jeff

Vohaul

hehe..as being the previous owner that did the igniton mod to the car in question...

No, i didnt cut the sub holes...)....

it was points before...now its electronic....distributor out of an 82...and following the famous scanned mazdatrix piece of paper diagram........from tim stiles, waay back when.....

and trust me, you dont want to turn it back into points
big headaches

Keaponlaffen

I know you didn't cut the sub holes, but the guy that had the car before you did, and he was a previous owner, so he can be a DSPO... yeah....

I need help with mixture settings though, does the Haynes manual tell you the correct settings? Or do I have to set them by exhuast gas? Anyone? Help?!


Jeff

Pele

iTrader: (28)

Sorry, No offense dude.

Thanks for shedding light ont he situation though. 79 with an 82 ignition. That helps a lot.

Yeah. You don't wanna turn the ignition back to points. That's true. Okay sounds to me that the mixture is screwed. Try the mixture proceedure that I put in another thread. Search for mixture and my name. It's a condensed version from the factory manual. The screw locations will be a bit different on your 79 carb as the instructions are from a 1985 manual. They should work though.

Keaponlaffen

K, thanks. I'll try that on Monday.... hopefully that'll kill some of the stuttering when shifting, and the backfiring too...


Jeff

SilverRocket

If you have to turn your mixture screw all the way out, I think there must be something else wrong with your carb. I don't have any good ideas as to what that might be, but I would definitely check all vacuum connections. Maybe something in your emmissions gear is messed up... sorry I can't be of more help.

peejay

1000rpm seems kinda high of an idle. It also sounds like it's idling a bit lean.

First things first... slap new plug wires and plugs in that bad boy. New plugs can't hurt, and ONLY use NGK BR8ET's unless you have an MSD. They should be about 4 bucks a pop. Change the pulgs every time you change the oil... trust me! I never liked the 2nd-gen plugs (BURxEQ? or something) because they seem to fould easier.

Now. Setting the idle... '79-80 ("SA22C", the best RX-7 ever ) carbs are different from '81-85, like practically everything else. There should be two screws in the middle of the driver's side of the carb. If you still have the rat's nest they might be harder to spot. The top one should have a head about 16mm across, flat blad screwdriver. This adjusts how much air gets to the engine at idle. The bottom one is smaller, is cross-headed (not quite Phillips) and adjusts fuel mixture.

BE CAREFUL. It's easy to get lost in this mess. Note I said the big one on top adjusts air. That means, it not only adjusts idle speed, but ALSO it changes the fuel mixture! Backing the screw out raises idle speed and makes the mixture leaner. 1000rpm seems like too high of an idle, and it *sounds* to me like the engine's idling too lean. So, after you replace the plugs and wires, re-set the idle speed back down to 800 or so. This will also have the effect of making the mixture richer... I think at some point someone tried to raise the idle speed by just tweaking the air screw, and didn't compensate with the fuel screw, so bringing the air screw back down should make things better.

hanman

Jeff,
peejay is giving you good advice. In addition to what he says make SURE that you don't have any air leaks. Cause it sounds like you do. Replace any hoses that are questionable. You have to get the idle down below 1k or you won't get the carb set right. If at idle you look down the barrels of the carb and see any fuel dripping in, then your idle is too high. If you have an air leak you won't be able to drop the idle low enough to set the mixture. An air/fuel ratio gauge can come in really handy to set the mixture.
hope this helps,
hanman

peejay

That's true too... possible to have a minor vacuum leak causing headaches. Also, you can run into trouble if you mess around with the throttle stop screw, which is what adjusts idle speed on the '81-85 carbies. I'm not sure how to baseline that screw, but it has a locknut on it so you can't just casually mess around with it, you pretty much have to have the carb off.

FWIW, I've found that off-idle throttle response really depends on the idle mixture and speed. If I set the idle speed up to 1k and/or adjust the mixture so that it idles smoothly (keep in mind, this is not on a stock engine...) it hesitates a little. For best response I set it so hot idle speed is between 650-750 and rich enough that the idle lopes. (between 650-750) I can't drive it on the street like this, it idles too low (around 400rpm!) when just off-choke. Right now it's around 900-950. When it was all stock it idled perfectly at 700-750 all day long, smooth as, uh, velcro. Of course it'd be easy to get around all this (and make more power) with a fully adjustable carburetor, or at least an '81-up carb that doens't have such a weird setup, but stubbornness and cheapness prevail.

When setting with a mixture gauge, I found that an O2 reading of .850v would result in lean misfire at idle. They have to idle quite rich to idle smoothly.