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my 79 SA runs pretty good but backfires from the exhaust when i take my foot off the throttle, idle is a bit low and to keep it running I have to open the mixture screw so it idles smoothly but then it smells really rich and the backfiring is worse. I think if I can get the idle up (its about 500 now) I could back off on the mixture a bit, but I and can't reach or even see the idle screw to adjust it. I know where it's at because I have another carb, but can't figure out how to get a screwdriver back there. I'm just having a bit of trouble getting the carb fine tuned. i have the fsm, but it doesn't seem to respond as it should
You might Jack up the right side and get under it looking for holes in your exhaust system. Any fresh air getting into the exhaust stream will reoxygenate the rich exhaust, and allow it to combust when it hits a hot spot, or gets lit off from incoming hot exhaust pulses. I had an 80LS that would shoot flames out the tailpipe any time I'd push it hard, and then let off the gas. It was really impressive at night, but garnered too much attention! The problem was a Pacesetter Header that had burned a hole in the manifold, allowing fresh air in...
Apart from that, I'm sure the carb guys will be along shortly to offer tuning tips,
no exhaust leaks except the air pipe, or there could be a leak at the manifold gasket i guess but, I did go thru the carb again, starting at 2 turns out on the air screw and 4 turns on the mixture screw and it runs pretty good now with minimal backfiring, but I still need to get to the idle screw and can't seem to get to it even with a long screwdriver with all the rat's nest stuff in the way. but as usual my posts are ignored mostly
Hey, Steve - have you searched and read the Related Topics, below? (*scroll down):
Might be worth a read and see what others have done to remedy the issue,
yes, I always search first, which usually doesn't help much, then usually when I post something, I can see someone has usually already asked the same question
Yep, that's typically how this board works; over the 25yrs I've been here EVERY question has been asked and EVERY problem has generally been solved, but not all posts link back to the eventual solution. Also, sometimes people use the forum to understand their problem, go off and fix it, and then never post back to say that it worked.
That said, there are far more carbd 12a cars out there than SE 13b which are my specialty, or I'd have better advice than what I offered above. Hopefully this will bump to the top and more 12a guys will see it. Keep at it, you've had it this long!
small leak at the flange, it's slightly warped. I thought it was sealed but there's still a small leak, runs good otherwise with minimal backfiring, just wish I could get to the idle adjuster
We're talking exhaust manifold flange leak, right? Gaskets are cheap and relatively easy to get to depending on your exhaust setup. It's worth doing that if the car had previously been running well. As mentioned, fresh air in the exhaust will always lead to backfiring.
Assume by "idle adjuster" you mean the adjustment for the closed position of the butterfly's? The carb manual shows this as an "off vehicle adjustment" I agree, it's very well hidden under the accelerator pump and can only really see it with a mirror. It also has a jam nut and I believe you'll need to remove the carb to accurately adjust it. I'd leave all the cables attached and just lift it up, off the spacer. If your wanting to increase idling by 250 RPM, I'd start at 1/16 to 1/8 turns in.
That adjustment is for the final closed position of the primary butterfly and can be very sensitive. Its not really an idle speed adjuster. The opening is meant to provide just enough air to let the engine idle with the idle air and mixture screws adjusted to that air flow. You should look else where for your idle issue. I suspect exhaust air leaks is causing the back firing. The low idle may be a clogged idle circuit in the throttle body or some other circuit in the carb. Has the car sat for any extended length of time with gas in it that has any ethanol in it? Whats the history on the car?
