Fuel/Air mixture settings?

[77-Z]

My son's '77 Z is FINALLY on the road after getting new injectors, cleaning gas tank, new plugs/wires/cap/rotor, setting timing. NOW I'm needing some guidance on getting the FUEL/AIR mixture settings correct. Is there an "order" to setting the adjustable screws? Also, how do I set them? (screw with spring on the top of the throttle body. screw on the lower side of the mass air-flow meter. any others?)

As it is set now the car doesn't have much umph, even though I have good compression, am running NGK-5 spark plugs, etc. Just want to be sure I'm setting the items that I have control over. Thanks for any assistance.

Mark

Charlotte, NC

[sblake01]

Here's an article from Atlantic Z Car Club that you might find helpful. http://atlanticz.ca/zclub/techtips/afm/index.html

[FastWoman]

What sblake said.

The big screw with the spring atop the throttle body sets the idle speed. It regulates how much air bypasses the throttle plate.

There's only one screw adjustment for fuel/air mixture, just below the exit port on the AFM. It's factory adjusted, and it's not recommended you adjust it, although it might have been adjusted by someone else. It regulates the air bypass around the air flow meter and, as far as I can tell, is used for tweaking the fuel/air mixture at idle only. CW would probably richen the mixture, and CCW would probably lean it (opposite from the mixture adjustment screw on a carburetor).

Edited October 19, 2010 by FastWoman

[Powerglide]

Unless you are pulling a trailer or you weigh 500 lbs, the car should have plenty of umph. Suggest you check running fuel pressure. If that checks out, bump the timing 4 or 5 degrees and see how the car responds. Make sure the distributor is adding 24 degrees of additional advance as you rev the motor. You'll need a dial back light or balancer tape for that. Your motor should pull 18 inches of vacuum at a HOT 850rpm idle. If not, something is wrong. Clean ALL low voltage connections under the hood, starting with the WTS/CHTS. Look for and eliminate air leaks EVEREWHERE.

It's unlikely but brakes could be dragging also.

[TomoHawk]

The L28 engine (at least on a '78) has a timing indicator plate with advance markings in 5-degree increments, so you don't need the timing tape like V-8 engines usually use. If you can locate the timing notch on the balancer pulley, and give it a little dab of white paint, you'll be fine. You might clean off the timing indicator a little (passenger side of the big bottom pulley.)

Edited October 20, 2010 by TomoHawk

[sblake01]

Powerglide is correct with what he says. I've done this on a 280Z as well as other vehicles. You're talking about static timing, not advance. Tell me how you're going to read the 24 degrees initial adavance with the stock indicator plate.

[TomoHawk]

The timing with a warm idle on a 280Z should only be 10 degrees.

[sblake01]

You're still talking about static timing @ idle; the comments by Powerglide and myself have to do with initial advance upon acceleration.

Edited October 20, 2010 by sblake01

[Powerglide]

"The timing with a warm idle on a 280Z should only be 10 degrees".

EVERY motor has different preferences. One may like 8 degrees static advance. Another seemingly identical motor may want 15 degrees to run well.

You may think you have 10 degrees static advance in the motor. But unless you have verified TDC with the number one piston at the top of its stroke---you really have NO IDEA what your ACTUAL initial timing setting is. The balancer and timing plate may show 10 degrees. But it could be 5 degrees or 15 degrees for that matter.

[sblake01]

Oh, I'm well aware of all of that. I was just attempting slow his usual jouney off topic. I guess I really didn't help.

[Powerglide]

Understood. My post was primarily directed to Mr. TomoHawk.