It passes the "nobody's trying to sell me anything" test, the "I'm capable of doing it" test, the "it probably won't break my car" test, and the "fits my budget" test...but I can't say that I understand how or why it would work.
What I gathered is that water injection can reduce temperatures in the cylinder, delay detonation, and allow timing to be advanced. I've heard claims that it helped economy without retuning the engine. There is some ancilliary benefits, such has cleaning out carbon build up.
The system I linked won't be as effective as a professional system which actually squirts water into the intake, simply because it runs on engine vacuum. Injecting less at open throttle when you want more. It might only give the possible benefit of a humid day. But it also doesn't run hundreds of dollars. If you wanted to get more involved with it, use a 12 volt air pump for fishing bait buckets instead of the vacuum. Gets around the vacuum limits and allows testing on EFI.
The link you provided includes a link to a more complex DIY system that runs off the smog pump and provides more water for higher RPM, which would be an improvement on that issue, but I like the 12v pump idea even better because I would need it most at wide throttle + low RPM.
I think the ignition is very retarded right now, I haven't detected any lugging no matter how I abuse it.
I took a look at that article. It was light on details, and I'm not familiar enough with the smog pump to puzzle it out.
There was a comment following the article from someone who hooked the vacuum system one up to a fuel infected truck. It seemed to run better, but fuel economy dropped. Seems the injected water, or simply the air coming after the MAF/MAP sensor, may have caused the oxygen sensor to read lean. The extra fuel the system dumped in to correct for the reading may have simply been the reason for the performance increase.
When I first saw the original article, I thought of a little aerator pump that ran off a D-cell that I had. I could have been able to set up the water jar and injector under the hood, and simply ran an air hose through a convenient hole in the firewall. Then I could simply turn the pump on when needed.
My name is Steve and I am an ASE certified auto tech and an old school hot rodder. I have not worked on cars for a living in 15 years but keep my certs up for my job as a QC inspector in the automotive industry. If has been many years since I have worked on a Quadrajet carb but here are a few things I do remember about them. Also I will include a few other tips. If anybody has other suggestion/corrections please make them.
1) Make sure the carb is in good overall condition. Many of the Quadra jet carbs had plugs that leaked gas on the main body; they have to be sealed with epoxy. The floats in these carbs are made of plastic and over time can absorb gas and cause a higher than normal fuel level in the float bowl. The base plates were the throttle shafts went through are also known to wear causing another vacuum leak. Also make sure they are no other vacuum leaks on the carb, manifold or vacuum lines. Here is a couple of carb links. Some of these guys can do magic to the carbs. http://www.carburetion.com/quadrajet.asp http://www.carburetion.com/diags/4mv.jpghttp://www.smicarburetor.com/product.../productID/428
2) Make sure the choke opens all the way when warm.
3) I believe on some models the secondary air valve is adjustable. This can delay fuel delivery for the secondary venturi under acceleration. May improve mileage.
4) There are kits you can buy to adjust the fuel delivery of the carb. They will typically include jets, metering rods and metering rod springs(sometimes called power piston springs) Making adjust to the fuel curve can make a difference in drivability and mileage. Do not go wild with the changes. Always know which are the original parts from the carb are so you have a baseline. Only make one change at a time.
5) Check your fuel pressure it should be around 5 to 6psi. If much higher it could cause a rich mixture condition. Some people with carbs lower the fuel pressure a little(1 psi) in hope for better mileage. I would not use less than 4 psi with a carb.
6) Make sure the vacuum lines are routed correctly and are not cracked or broken.
7) Make sure all emission devices are working correctly. If one of these is not working correctly it will reduce mileage.
8) An aftermarket high performance ignition module and coil can also help. For a lack of a better explanation a bigger spark at the sparkplug.
9) Ignition timing. Most cars can handle a modest increase in ignition timing, 5 degrees is usually safe. Also make sure the distributor is in good working order. Make sure the mechanical and vacuum advances work. Also no slop in the distributor shaft bushings. Have the distributor setup with a custom advance curve if you can find someone that still does it.
10) Check the catalytic converter to make sure it is not plugged.
I think that any efforts will be futile until I accomplish your #1 tip, making sure it works right.
It currently has an intermittent high idle condition; usually it idles way too fast. Even after I manually push the fast idle cam down and the idle RPM goes down it's still too fast. I recorded that video the other day and of course that day it behaved abnormally well, coming down off both of the fast idle cam's steps with throttle input (I ran out of video space before the second step).
Then under heavy throttle it bucks as if it's not getting enough fuel but making the same power at higher RPM is smooth, so I'm not sure it's a fuel supply problem.
Looking at the other tips...they are definitely some good things to discuss.
2. Is there any way to make sure it's opening all the way during normal driving with the air cleaner on?
3. On a related note, how can I confirm if the secondary air valve is opening at all?
4 and 5. Definitely things I should look into.
6. I had a vacuum leak last Saturday and took care of it, and intend to replace all old-looking lines even if they aren't leaking. For that purpose I bought some more line.
7. I removed the smog pump, thinking it could have no positive effect on fuel economy (but that its drag could waste energy). I do want to check my EGR and make sure it's working properly.
8. Might be a worthwhile upgrade in the future.
9. I do need to make sure the advances work, I've been thinking of checking that; I'll have to look up how to do it. As for increasing it a little, I'm not sure I want to. I'm afraid that I'll get spark knock and destroy the engine. I'm having trouble breaking my low RPM high gear habit (stick shift).
10. A modern one is easy to check, but I don't know how to check this old-technology cat. I've looked and photographed inside and it doesn't appear plugged, just badly designed. A new one is not currently in my budget but I don't think I want to delete it entirely.
11. I should probably look into that.
12. I think my fan spins pretty freely by hand when cold. I know it spins easily but I don't remember if it stops after a couple revolutions or keeps going. It definitely isn't stuck locked.
I would either fix or replace the carb. The next thing I would do is to install the air pump/AIS back on to the engine. The air pump supplies air to the cat which needs the air to burn off the excess HC and CO. Without the extra air the cat can go bad. Air pumps use very little horsepower. The cars of that era were calibrated with all of the emissions equipment and when it is taken off or not functioning it will really kill the mileage. I had many customers that took off the smog equipment and could not figure out why the engines ran poorly. I always ended up reinstalling all of the emission equipment.