Reset mixture after replacing old spark plug wires

[schoward]

Recently found my SC to be taking just a little longer to start and maybe the slightest bit of laziness to the idle (very slight). Car however ran fine and did a 1,000 mile trip no issues like always.

As I had a spare set of fresh braided Berus in my cabinet for years, I figured it may be time to replace my 12 year old Berus - certainly couldn't hurt and symptoms were a sign of tired wires on my car.

Sure enough, after just replacing even the driver side bank of wires, starting was crisper and idle stronger. I guess 12 years was it on the old Berus. Did the full set / right side wires also but it seemed the left side was it (likely cooked from exhaust heat).

Question - I noticed idle is now strong to the point I had to turn the screw right maybe 1/8 turn to calm it back to 900 or so hot. Do i need to reset the mixture now also? Could be it leaner also now?

The idle screw turn was literally the first screw turn I've done in 4 years and my idle and mix was set perfectly at that time and ran great since. It is no big deal to do it, but does strong ignition now possibly require a mixture adjust or just the idle? Can the change in ignition necessitate a mixture adjust? I think the answer is probably yes, but curious if any opinions?

Thanks.

[Dr J]

If idle is good, and you are having no other problems, I would not touch the mixture screw unless you have an AFR or CO meter.

[dhanl82]

Good point, I agree, do not touch the mixture.

[schoward]

It was 56 degrees here in NJ so had the opportunity to drive it alot today and check mixture (I use a dwell/duty cycle meter on the CIS test port for years and it works great). I am fully CIS stock with the O2 sensor /lambda connected and all working.

As I suspected from just driving and observing, the mix (reading from the O2/lambda port) was SLIGHTLY leaner than when I set it last. Idle rock solid at 950 when hot. Ever so slight - like instead of the dwell meter dancing around 40 where I set it last (just slightly rich), it was more like 41-45 (near 50% duty cycle). I like it slightly rich but the difference is so slight. I did a cursory air leak test and did not find anything so will leave it for now, just drive it and see what I find.

Unless an air leak suddenly developed (possible but maybe doubtful here), wondering if the better ignition/spark is giving more complete combustion thus O2 is sensing leaner / less fuel)?

[T77911S]

mixture is the last thing you check.

check fuel pressures if you have gauges
if not, it might be worth it to check the inlet screen on the warm up reg (WUR) just to see if it is getting clogged.

check your timing then check mixture.
you can manipulate the sensor plate at idle to see if changing the "mixture" does anything worth noticing.

how old is your O2 sensor.
since it is connected you may consider replacing it if it has a lot of miles on it