What's your Weber carb gas mileage ???

[overs10ded]

With my 3ac my best was 34mpg on a tank! When I first put it on, 27mpg "out of the box"! I spent a month playing with jets, air correctors, and idle jets and drove it for 3 years of over 30mpg per tank until about a year ago after leaving it sit for 3 months evidently the mech advanced seized up and my wife was the one driving it and telling me the fuel mileage was falling off so I would check timing, clean plugs, and set mixture. Then the timing belt broke and that engine was burning a quart every 300 miles any way! Now this week I have swapped a 4ac (used) and am chasing my butt again! First off the distributor mechanical advance was seized which was a problem that came over from the 3ac and was the issure w/old 3ac and mileage and I was tuning to that...So once I (with help from Jimcrazy and Petros) figured that out and got the advance working again, I've had to start over and I'm dailing it in...again! Tedious for me because I'm tuning it for my wifes feather light foot-luggish driving. So there can't be "the bog"! The F6 emulsion tube seems to help that over the F50. I am just now going out to downsize the mains from 145's to 140's with 170, 180 correctors, and 65/55 idle. Just reset my float to be higher than it was, mine is a brass float and was 44.5mm and 54mm - I changed it to 41mm and 51mm. Seemed to help but after the 140 swap I'll test and see how things are. Right now the idle mix is 1 7/8 turn out and the first 1/4 pedal is excellent...then with more pedal it starts to "drag" a little, and the secondaries are a continuance of the "draggy" feel, but let off the pedal and she catches up and that sounds lean, but I've found this 32/36 acts the same rich or lean and you have to determine which way it is then go in the opposite direction. I'll let you know what I end up with!

Good times!
Bruce

[overs10ded]

It drove very nice with the 140's and 180/170 air...I'm going to try 180/180 air as that is what I have. Also 140 is the smallest main I have. I want to try a 135 main and also a 190 air! On the F6 emulsion tube I mentioned before, that is only on the secondaries, and I have a F50 on primaries. I'm going to fiddle a little more with the idle jets to and see if I can get them a little leaner than 65/55 but my mixture screw is at 1 7/8 turns out.
I have found that leaving the tiny "c" clip off the choke shaft alleviates the worry of loosing it every time I pull the top off the carb, just hooking it on and popping it off for test driving.

Good times!
Bruce

[overs10ded]

At this time with 140/140 main jets, the 65/55 idle jet, the 180/170 air combo works best for this car. The 180/180 made the "bog" higher in rpm and more noticable. The 180/170 is pretty smooth! We'll see about mileage with this idle jet. Tried a 60 idle jet and that also exaggerated the bog too, with these air correctors (could richen the air correctors and use the leaner 60 idle jet I suppose). So this combo is working and has been tested by the wife who says never smoother and much zippier than the 3ac!

Good times!
Bruce

[Mad_Marx]

So far, 25 around town, 28 highway, but I do have a mild cam, and it's not an actual Weber, it's a Chinese Empi. Had a Weber on the last car, it did slightly better and held a tune longer.

[xirdneh]

From Pegasus online Weber sales
The Weber DGV series are very sensitive to changes in float level.
In fact, most of us using these carbs in racing applications never change jets but check and adjust the float level at least once every race weekend. If I'm reading your email correctly, your float is set at 44mm droop height instead of the recommended 51mm. This will cause the carburetor to run rich, which will waste fuel. Re-setting the float height to 51mm droop and 35mm (measured from the bottom of the float) with the float tab just touching the ball of the needle valve will result in a much leaner mixture throughout the RPM range.

Another easy thing to check is that the choke is opening fully when the engine is warm. If the choke stays closed, it can cause rich running and a loss of power. It will literally choke the carburetor, preventing it from breathing freely.

[helipilot77]

It would be interesting to have someone be willing to weld in an O2 bung and record a table with different Webber jets and their respective air/fuel ratios. I would do it, but I'm running a stock AISIN carb and it seems to run so well that I would rather not mess with it. If number were acquired for sea level it seems like calculations could be made to lean up the jets for higher elevations.

[Petros]

I have known people that were putting webers on cars back in the 1970's including some friends. all of them ran much better with proper fuel and air jets. There used to be shops that specialized in tuning the weber carb, they would use an exhaust gas analyzer to get the jets correct. Not likely enough people using this carb any more to find a shop that does weber work locally any longer.

I do not recall that the float was ever an issue, though it would make sense since it is very sensitive to fuel pressure (and the reason it needs a fuel pressure regulator).

[overs10ded]

Before the Weber, the Aisin which was bleeding fuel but ran well, fuel log entries were; 21.7, 21.5, 24.1, 24, 27.7 (highest), 23.3, 22, and last tank was 22. When I first put the Weber on the 3ac, my first tank was 25 and the next two tanks I recorded at 24.5 and 24.1. Then I adjusted the float and the next tank was 26! I tried to fill the tank after each change and at the time of the Weber install I was taking meticulous fuel records to the extent of only fueling at the same fuel pump and car position at the pump at the same station and fill it to the filler neck lip! The next tank after that one shows 30 and then 31.2 for the tank after that one! The jets were 140 pri, sec, 160,170 air, 60/50 idle, and F50 emulsion tubes. After that tank, 32.7. I then changed to a 145 main primary and switched the airs to 170,160 and show 33.5 then my all time high 34.53. Then the next tank was 32.1 and then 31 when I quit keeping a fuel log-it is my wifes car and it was just too much to stay on top of the fueling which is key to keeping REAL fuel records! I never touched the floats or jets again for 3 years and the car did settle into a high 20's mpg range. However as I have mentioned that after we returned from a 3 month vacation, the car didn't run well and was using LOTS of fuel-and I just found out that it was from a seized mechanical advance in the distributor that occured evidently while we were on vacation. I just addressed the mixture, clean plugs, check timing, although it started pinging so I thought it was bad gas from the station...The mechanical advance!! Now it works again!! I am now running the 4ac and am tuning the weber but have not started to log mileage yet. Don't have enough money to fill the tank! lol

Good times!
Bruce

[Petros]

running too lean will not yield the best fuel economy, it almost sounds like your mid range is on the lean side.

funny thing about fuel economy, too rich or too lean will yield poor economy, it has to be at its optimum fuel air ratio to deliver the best fuel economy. That is where the mixture burns hottest and delivers the most power for the amount of fuel burned.

Keep up the good work, it is interesting to see the changes. BTW, the larger 4ac engine, with the optimized fuel/air mixture set, should deliver very similar fuel economy as the smaller 3ac IF YOU DRIVE IT GENTLY. For me it is very difficult to drive it gently when I have the extra power available, I have to pull out into hwy traffic and go up and down steep gravel roads daily, and the extra power of the 4ac is much appreciated to make the driving much less harrowing. Though I know it does not deliver the best fuel economy, so an exact comparison between the 3ac and the 4ac is difficult to achieve. Driving style changes when you have the extra power. The Tercel should have come with 90 to 100 hp from the beginning, which is about what all of it's competitors had.

[overs10ded]

I am really happy (read LUCKY) with this worn out 4ac and how good it runs! I didn't weigh before and after but my machinist cut a bunch off the flywheel and it revs noticably quicker than the 3ac and also I removed a easy 50# of A/C items too-everything firewall forward and even cut the A/C compressor and idler bracket off to just include the alternator. The midrange and secondary transition needs some work but the first 1/3 throttle is super snappy and pulls hard-I was really surprised-it's almost fast! I'm extra picky, my wife says it is good-and "peppy"! I do have worn out throttle shaft bushings and ordered the bearing bushings for the 32/36. Next should be to replace the tiny downpipe with a 2"+ downpipe to the cat convertor I think would help on the cheap!

Good times!
Bruce