[Cliff R]

I tune for a living and don't use an AFR or vacuum gauge. We tune these engines for best results in all areas.

Idle tuning in is the easiest of all because you can simply listen to the engine as you lean up the mixture screws and hear a speed change when you just start to go lean. IF you had either a vacuum gauge or AFR gauge or both you'd see the vacuum start to fall off just a tad and the AFR start to go a little leaner.

As soon as you hear an engine speed change when turning the mixture screws in, stop, and back them up till you reach smoothest idle and/or highest RPM. This is usually about 1/2 to 3/4 turns with a Q-jet, it could be 1/8 turn with a Holley style carb.

It's always to er just a tad rich vs lean at idle, at least if you want the minimal drop in RPM's when the trans is placed in gear as mentioned above.

I'll add here that 99 times out of 100 when you see significant drop in engine RPM's when you place the trans in gear the carburetor is not the problem. It's going to be the POS spring/weight kit that someone stuffed into the distributor because someone on one of the Forums or one of their beer drinking buddies told them it would make another 100 HP over the stock parts!.......Cliff

[Kenth]

I have found idle issues is solved in the idle circuit.
The orifices thru the main jets/rods are always larger than the idle fuel supply tube restrictions so altering/adjusting the main jets/rods/power piston/spring circuit will do NOTHING for idle settings.
The idle circuit is a stand alone circuit wich can be altered/modified/adjusted for the engines needs.
And, nozzle drip is a result of too high level of fuel in bowl and/or to much opened primary throttle blades, in turn due to a too lean idle circuit, has very little if anything to do with the primary rods position in the jets.

FWIW

[Navy Horn 16]

Originally Posted by Cliff R

I tune for a living and don't use an AFR or vacuum gauge. We tune these engines for best results in all areas.

Nobody here doubts your expertise Cliff, but since we don't do this for a living, we need the tools.

I totally agree that not getting hung up on the numbers and tuning for what the engine needs is critical.

Chasing a digital number on an AFR gauge (especially by taking the air cleaner on and off) is no way to get to a driveable condition. Set it up with the air cleaner on, verify timing is correct, and max vacuum is going to be really damn close to perfect. Maybe half a turn one way or another with it in gear.

[ta man]

Cliff ...thought you were retired?

["QUICK-SILVER"]

This air filter base touching any plug wires when you set it on? Or throttle lever?

This 78 carb have Pontiac external bowl vent tube and breather base not have?

Clay

[Cliff R]

"Nobody here doubts your expertise Cliff, but since we don't do this for a living, we need the tools.

I totally agree that not getting hung up on the numbers and tuning for what the engine needs is critical."

Nothing wrong with buying tools but for sure apply some common sense before buying/using them, especially for idle tuning. Back out the mixture screws for smoothest idle and highest RPM, then start turning them in until you here the slightest change in idle quality or RPM's drop off.

You are going lean at that point, no meter required to know that. Back them out about 1/4-1/2 a turn each or till the engine smooths back out and best idle quality. You are DONE at that point with idle tuning.

I'd add here that 99 percent of the troubled vehicles brought here with idle issues are distributor related. I absolutely LOVE the fact that every Forum you go to has at least half a dozen "gurus" that will tell you to install some sort of cheap POS distributor spring/weight kit. Between poorly educated folks that need to stay off the Forums and keep their day jobs to companies selling junk springs and weights I've made a nice living removing all that crap and throwing it in the scrap pile!

"Cliff ...thought you were retired?"

I'm still in the parts business but getting out of everything else.

Stopped doing engines 4 years ago, only one transmission since then and it was for a friends 1984 Olds 442 (200-4R).

No carb restorations or plating work whatsoever and just taking in a few carbs here and there for the beer fund.

Most of the carbs I'm doing are just rebuilt or "restored and don't work, so it's nice an clean and I just have to go in and throw out all the junk parts and set them up for the engine they are sitting on........

[fiedlerh]

Many years ago I had a job where I had access to all the latest tune up equipment and 4 gas emissions analyzers. On a stock car with a stock cam and an adjustable idle mixture, we set idle screws to the highest vacuum. This got us around 6 to 8% CO readings which was very rich with eye-burning exhaust.

Then we used the factory method as mentioned by Cliff, where you turn in until the rpm drops and then back out a little bit. This got us around 3% CO readings and the engine ran much better and no stinky exhaust. With a tight newly rebuilt engine it would even be happy at 1.5 to 2% CO. What you really want is maximum CO2 readings.

The "max vacuum at idle" method is likely valid with log-style intake manifolds used on old inline engines.

[ta man]

Originally Posted by fiedlerh

Many years ago I had a job where I had access to all the latest tune up equipment and 4 gas emissions analyzers. On a stock car with a stock cam and an adjustable idle mixture, we set idle screws to the highest vacuum. This got us around 6 to 8% CO readings which was very rich with eye-burning exhaust.

Then we used the factory method as mentioned by Cliff, where you turn in until the rpm drops and then back out a little bit. This got us around 3% CO readings and the engine ran much better and no stinky exhaust. With a tight newly rebuilt engine it would even be happy at 1.5 to 2% CO. What you really want is maximum CO2 readings.

The "max vacuum at idle" method is likely valid with log-style intake manifolds used on old inline engines.

Eye burning exhaust is lean to me..

[Formulajones]

Yep, too lean will have a horrible smell and burn your eye's too.

I prefer to adjust the idle mixture for the "strongest" idle, which is usually a pinch on the fat side in most cases. The stronger idle just works better in day to day driving with no monkeying around with the throttle on a luke warm start and just better all around in gear idling in all conditions.

How rich that needs to be just depends on the engine setup and camshaft. I find that an engine with a working heat cross over can get away with a leaner idle mixture without exhibiting wonky idle problems, while no heat cross over, or a restricted cross over tends to need a little more idle fuel to be happy. Either way with todays gas I prefer them to be a little richer rather than leaner anyway.

[fiedlerh]

HC will go up too rich and too lean, so both ways will burn your eyes. Most restored muscle cars I happen to be behind are running way to rich. A little black smoke is a giveaway.