Fuel mileage 32ADF vs. 34ADF

[kmoses]

What kind of mileage should I expect from a carbureted 2L spider? My '79 spider has a single plane intake, 34ADF, 4-2 exhaust manifold, free flow exhaust and it runs fantastic! The car starts easily, idles smoothly, accelerates evenly and is a joy to drive but I'm only getting 17 mpg on the highway (my Avalanche gets 17.5 on avg.). Is this mileage normal? Would dropping back to a 32ADF help with the gas mileage without cutting the performance noticeably or should I be looking at a newer Weber like a 32/36 DFEV?

[silvadw]

i have the same car as you. My 34ADF was new when i put it on about 18 months ago. My distributor has a new cap and rotor, and i have new-ish plugs. The motor was a rebuilt unit and probably has 7,000 miles on it. car gets tuned about every 6 mo.
i get 26-29 mpg suburban and freeway combined. Best fuel economy is 45-50 mph
my driving style is neither aggressive nor conservative, but i do wear heavy shoes
do you have a heavy foot?
maybe you have a leaky carb?
When was the last time the car was serviced/tuned?

[djape1977]

consumption varies A LOT depending on driving style on carbureted cars

[Nanonevol]

I have a 34ADF on an 1800 and got 22 mpg when I checked but haven't run many tankfulls. I think it should be better and wonder if it could be the jetting. Here's what's in it:
Idle: 55/80
Main: 140/125
Air: 180/170
Accel pump 50
emulsion tubes F20/F7
I experimented with what I had on hand and the car starts, idles and runs great. Maybe that 50 accelerator pump is pumping more than really needed or something else is going on. Always curious what other people have for jetting. I may get around to some more experimentation some day.

[aj81spider]

17 on the highway sounds pretty low. I have an 1800 with a DMSA and get 23-24 on the highway and about 20 around town. I don't drive for fuel economy - it pretty much goes to red-line at every stop sign.

[johndemar]

What's fuel mileage?

Honestly I didn't notice a difference when switching from the 32ADFA to the 34ADF, but I don't pay much attention to that.

17 does sound a little on the low side, but you'll never see modern day MPG's out of these cars.

[kmoses]

Everything is new rotor/cap, wires, plugs, Marelli Plex 201, 13° BTDC @ 950 RPM. 34ADF /250 new when installed 5 months ago, with jets as follows: Idle 52/60, Main 125/135, Air Correction 175/190, Idle Screw 1 1/4 turns in, Air Mixture Screw 1 3/4 turns out from seated, Float 7mm & 14mm, new electric fuel pump = Facet Cube 40-104.
No emissions at all not even a catalytic converter. The engine is 2L with 1800 head. I would love to get 20-22 mpg.
I just don't know what else to check.

[Dawgme85]

My '77 1800, 32 ADFA, electronic ignition, 4-2-1 manifold, replacement catalytic converter, typically gets 20mpg. On a recent 200 mile (spirited) drive, it returned 25mpg. YMMV

[kmoses]

Today I installed a rebuilt 32ADFA that was never installed after I bought the the larger 34ADF. After some jetting changes and a 30 min. ride I can say that running on the 32ADFA primary feels "crisper and more responsive" but when you put the pedal to the floor you know something is different, the acceleration that was there with the 34ADF is now gone. I'm starting to think a 32/36 DFEV my be what I need on my spider.

[silvadw]

I have a 34ADF on an 1800 and got 22 mpg when I checked but haven't run many tankfulls. I think it should be better and wonder if it could be the jetting. Here's what's in it:
Idle: 55/80
Main: 140/125
Air: 180/170
Accel pump 50
emulsion tubes F20/F7
I experimented with what I had on hand and the car starts, idles and runs great. Maybe that 50 accelerator pump is pumping more than really needed or something else is going on. Always curious what other people have for jetting. I may get around to some more experimentation some day.

on my 34ADF
idle 50/90
Main 120/135
Air correction 145/180

reasonable mileage and accelerates like a scared cat

[carl]

I think your main jets on the 34 are reversed, on a 32 the mains are 125 on the primary and 140 on the secondary. I would replicate the jetting of the stock 32 on the 34 to start with.

Make sure your tires are properly inflated, nothing with suck down mileage like low tire pressure. Also depends on the condition of the motor, do a compression test.

Most of your steady state cruising is done on the idle jet, Secondary will come into play only when dipping heavily into the throttle.

[Nanonevol]

I think your main jets on the 34 are reversed, on a 32 the mains are 125 on the primary and 140 on the secondary. I would replicate the jetting of the stock 32 on the 34 to start with.

If this is for me...I'm using what works after some experimentation. It seemed "logical" to me that the secondary jets would be larger but that logic is not built on any knowledge or experience. I found Brad Artigue on another forum suggesting the primary main be larger. Anyway, this is what works well for now and replicating my 32 jets on my 34 gave no love. Emulsion tubes are a whole 'nother mystery. Thanks for the input.

[silvadw]

If this is for me..[/quote]

yes.
I did significant research on jetting when i bought my 34ADF as i couldn't get it to run correctly.
The jetting i have came with the carb. I ended up taking the car to a smart fiat gut who tuned it properly, i.e. adjusted idle and mixture screws properly. he still didn't tell me what he did. I haven't pulled the car apart to see if jetting is same.

However, the primary was always smaller than the secondary in my research. I believe that helps fuel economy

[131]

In Oz the 34 ADFA was stock on the 2 litre.

Primary, Secondary.
Main Jet: 122, 130
Air corrector: 170, 180
Emulsion tube: F20, F5
Idle jet: 50, 90
Float level: 6mm

On my 2 litre, with mild cams and a 34 ADM, I consistently got around 27mpg. (10.5l/100km)

[jagonza]

is an Australian gallon like a UK gallon or a USA gallon ??