WOW! You've done quite a lot!

I suspect you've still got multiple issues going on, although you've apparently eliminated most of the major stuff.

There's no way the yogurt cup test was inconclusive when I did it, so I'd say if you're scratching your head as to whether there might be a leak, there's DEFINITELY a leak somewhere -- or multiple leaks. However, they would probably be small leaks. As a guideline, my intake system would hold pressure for maybe 20 sec when I "inflated" it.

The glue blobs in the AFM don't look factory to me, so perhaps someone did molest it. The blobs don't look neat or small enough, and I believe the blob in the center should be a dot of red lacquer (?), not silicone. So I'd say that's your most likely culprit for rich running. I'd look at the Atlantic Z site for the article on adjusting/calibrating the spring tension ("the beer can method"), and I'd go through the tests in the FSM.

The TPS is your other potential problem spot. I'm not sure what is left/right on the thing, but it needs to be calibrated not by RPM, but by throttle position. Make your adjustments with the engine stopped. You want the idle side of the switch to make contact until the throttle JUST MOVES FROM ITS REST POINT. At that point neither side of the switch should make contact. This should continue until you're maybe at 2/3 throttle, at which time the other side of the switch should make contact. You should adjust and verify this with a multimeter.

Although it's tempting to suggest you need an "anti-resistor" , I think addressing these last small issues will bring you home. When you think your engine is running about right, you should replace your plugs, drive for a hundred miles or so, and give your plugs a read. You want a nice mocha/tan coloration on the insulators. If the insulators are black/sooty, you're still running too rich. If they/re white/gray and chalky, you're running too lean.

Just remember that the TPS has 3 positions. Idle enrichment (when idle contact is touching at zero throttle ), no enrichment (cruising), and full enrichment (when contact is touched during heavy acceleration).

If your TPS is touching the full enrichment contact during partial throttle at crusing speeds, you will see a huge drop in your mpg. I would suggest looking at the service manual and make sure it is working correctly. It's a common hack for previous owners to bend the contacts so it richens the mixture early to overcome other issues.

I also agree with Sarah. You've got vacuum leaks. I would try using carb spray or a propane torch (unlit obviously) to see if you can locate those leaks.

I believe I have my TPS adjusted properly now. Before the left contact was always closed. Now the right contacts when the engine is in idle and open at about 1200 rpm the right only when the throttle is wide open (punch it). I believe that this was the root of my problem. I am a little aprehensive of adjusting the AFM, I have read the atlantic Z article, perhaps this weekend I will carfully try to adjust it. Also a good time to revisit the yogurt. At work I use mapp gas not propane is this suitable for testing or to "volatile".

When I filled up last I drove home, pulled my plugs and cleaned them so as to see how I am doing after the 10 gall.

Thanks again both, for pointing me in the right direction. I wonder if the PO was trying to "hot rod" the engine now, 15 deg advance, tampered AFM and full trottle bent in on the TPS.

I believe I have my TPS adjusted properly now. Before the left contact was always closed. Now the right contacts when the engine is in idle and open at about 1200 rpm the right only when the throttle is wide open (punch it). I believe that this was the root of my problem. I am a little aprehensive of adjusting the AFM, I have read the atlantic Z article, perhaps this weekend I will carfully try to adjust it. Also a good time to revisit the yogurt. At work I use mapp gas not propane is this suitable for testing or to "volatile".

When I filled up last I drove home, pulled my plugs and cleaned them so as to see how I am doing after the 10 gall.

Thanks again both, for pointing me in the right direction. I wonder if the PO was trying to "hot rod" the engine now, 15 deg advance, tampered AFM and full trottle bent in on the TPS.

Possibly PO trying to hot rod it. FWIW, this motor does like to be advanced a little. They timed it low to help with emissions. Most people are running it around 13 degrees advance, some as high as 15. Also, on the TPS, I believe it should make contact before wide open throttle, but you will have to have your foot in the gas quite a bit. I would say 60% or more throttle. That is just off memory though, not an actual measurement. You will want to make sure this is right or you could be running a bit lean under some moderate acceleration scenarios.

HA!!! I found something new. Thanks to fastwoman for making me to revisit the AFM.

Remember my earlier post when I wrote how my fuel pump always ran? now I know why! Someone has mucked with the AFM in the past for sure. look at these pics the old one I posted and the one from the Atlantic Z site. notice how the wiper contact is about 8 mm from 0 volts when the meter is completely closed, and how the shut off switch is not even touching, and where it should be. I did a quick test by gently moving the fuel shut off and it works!

I am down to about a half tank now and I think I am getting about 15 mpg. after I am on empty again I will calculate My mpg then make an adjustment to the afm. I really think

I have found the two major culprits but still need to get my vacuum up,

Stay tuned

Ah! Well, now! Yes, you have a very good find there, indeed!

So do you see the red "Glue Blob" label in the top photo? That's the set screw for the wiper. Loosen that, and re-set the wiper arm to where it travels from end to end on the trace (rather than undershooting the low end and overshooting the far end).

I'm trying to remember the year of your Z. Does your fuel pump use the shutoff switch in the AFM? If so, you might be able to carefully bend the arm of the switch mechanism so that the switch will stay closed when the engine is running.

But yes, moving that wiper arm will definitely make your engine run leaner! I'd say that's your smokiest gun! If I were you, I'd do a full re-calibration of your AFM. If you're even a little bit careful and thoughtful about what you do, it's not going to fly apart in a million pieces and ruin your day.

Fastwoman, My car is registered as a 78, but another Z owner at a meet up here in Seattle looked at my engine and vin number. He suggested that my car was actually an early 77. He was correct. My car is indeed a 77. The shut off arm and wiper are linked so if I adjust it back to the correct setting I should have fixed two problems.

I would like to do a complete recalibration of the AFM but I am a little confused regarding the pop can method. Looking at the Atlantic z article I can see how to do it but I am unsure how much weight/water should be used. Are his weights posted the ones I use or just what he found he needed. Can you clarify?

Edited July 8, 201114 yr by grantf

If you use his weights, it should calibrate it correctly. I followed that method and I was spot on.

Interesting about the year of your car. Mine is a 78, and they did move the fuel pump cut off to the oil sending unit. Mine doesn't have the cut off on the AFM. That should confirm that yours is the earlier model.

I think it really helps to use a single pan electronic balance if you have one. You can make your weight however you wish.

FAIW, Zed Head and I played around with a calibration method that used voltage output as a function of weight against the air vane. I think it's a valid approach, but unfortunately neither one of us had an AFM we could 100% trust as being correct. Anyway, you can find the relevant posts somewhere around #225 (both before and after) in this very long thread:

http://www.classiczcars.com/forums/showthread.php?40392-76-280Z-Question-on-dist-manifold-vacuum-dist-timing-fuel-pressure-brake-booster/page11

I think I may purchase a cheap electronic scale. My identical twin brother is using one that works great for mixing epoxy hardener for his "flying Z" http://flyingbackward.blogspot.com/

I've got an electronic food scale that works well and measures to the tenth of a gram. It was spot on for me.

Ok, I ran my the 10 gallons through. I calculated 16.7 MPG. Hey quite the improvement!

I have adjusted the AFM both the wiper setting and the spring tension with 148 grams of weight, it was about 12 teeth off. the car seemed to be a little gutless so I backed the tension down about 4 teeth, Wow what a difference! I thought the car was running good before. Now it seems like a different car. 10 gall added and I will calculate again my mgp. I think I am there now! Also I will pull the plugs look at them clean and read them again after 100 miles or so. Stay tuned and thanks again.