Weber fuel mix/mpg

guards73/2.0 · guards73/2.0's Garage

I have 40 IDF's, stock 1973 2.0 in good shape. The webers were
installed by the PO, and recently pro rebuilt by a reputable shop.
The weber kit was ordered for this car, and came with Weber's ecommended jets for a 73 2.0 914. The car runs rich. What kind of MPG should I see with properly jetted Weber 40's in a stock motor? My odo doesn't work ( gee..imagine that.. on a 914?) but it feels like 10-15 MPG, (and a black tailpipe)which is tough to take @ $1.50 plus, and probably bad for the motor.

Kevin Powers · 10-13-2002, 06:32 AM

here's what you need to do first. pull one of the idle jets (i know, just use a tiny screw driver). then pull one of the stacks and note the numbers on all of the components. air correction, main jet,emulsion tube. post these #'s, that way you and the rest will know what the starting point is. unless you foot is in the throttle hard you are on the idle jets most of the time. this is a weird time consuming proceedure. an engine builder that posts here and other places says he gets 30+ with his foot in it (i can only wish). what type of fuel pressure reg are you running? 19 to 20 was the best i ever achieved. funny though, that was the epa rating for the cars stock. hell, my international pu w/ a v8 and truck 4 spd gets 16 on the freeway,go figure. run the fi go crazy and broke, switch to carbs put on a staight jacket and fail emissions testing. see piece of paper on wall w/ circle and "bang head here".

kevin

guards73/2.0 · guards73/2.0's Garage

Does anyone out there have the book "Weber Carbueretors"?
It lists the recomended guts for 40 IDF's with a 73 2.0 914.
I need to find those values, because that's what I have. I probably need bigger ( less fuel, right?) idle jets.

Kevin Powers · 07:42 AM

that's why you would be running rich. the larger the # the more fuel delivered. a #55 jet flows more fuel than #50. you can get a pretty good book from cb "BOB TOMLINSONS ORIGINAL WEBER TECH MANUAL". it explains how these carbs work in a language you can understand, and has a very good problem/trouble shooting section. what is really in your carbs can only be known by removing the items i mentioned. it's like buying an engine,you only know whats truly in it by taking it apart. trying to determine the jetting items by a spec sheet is pointless,you have know idea what the po did or did'nt do.

here are the "basic guide lines" from their (cb) book. for a 1835-2000 cc motor. venturi 28mm, main gas 145, main a/c 220, e/tube f11, idle 55. the jetting issues is adressed very well at the aircooled.net site in one off the tech articles.hope this helps.

kevin

guards73/2.0 · guards73/2.0's Garage

I have 50's now.

Kevin Powers · 10-13-2002, 07:49 AM

what type of fuel pump and pressure reglator are you presently running?

guards73/2.0 · guards73/2.0's Garage

I have the usual round chrome dial type reg with a 4-6 psi rotary
pump ( new).

Kevin Powers · 08:34 AM

f.p. set at 3.5 to 4 max. it is my understanding that over these figures can over drive the float valves, resulting in a continual "rich" condition. at one point in time i ran a facet type and unwhittingly did not have a fp reg. i put on one of those chrome/adjustable ones but never trusted it. i guess a inline fp guage is probably a good idea.

kevin

scg · 10-13-2002, 10:29 AM

According to the book (Weber Carburetors):

For a 914 2.0 conversion, they have three (3!) conversion suggestions:

(1) -------------- 40 IDFs:
Main Venturi: 32
Aux Venturi: 4.5
Main Jet: 125
Emulsion Tube: F16
Air Correction Jet: 180
Idle Jet: 50
Pump Jet: 50
Pump Ex.: 55

(2) -------------- 44 IDFs:
Main Venturi: 36
Aux Venturi: 4.5
Main Jet: 135
Emulsion Tube: F11
Air Correction Jet: 175
Idle Jet: 50
Pump Jet: 50
Pump Ex.: 55

(3) -------------- 48 IDFs: (!!)
Main Venturi: 40
Aux Venturi: 4.5
Main Jet: 150
Emulsion Tube: F2
Air Correction Jet: 180
Idle Jet: 55
Pump Jet: 50
Pump Ex.: closed

Comparing these with the settings Kevin Powers found shows the amount of experimentation you're in for. Fortunately, the parts are fairly inexpensive!

30mpg?!? I, too, could only wish. I suppose...if I diconnected the accel pump...

My problem is I can't get over using the right pedal as an on/off switch -- it's just too much fun

I'm only on my second tank since my conversion, but I managed 18mpg with the first one.

Hope this helps.

HarveyH · 10-13-2002, 12:25 PM

1974, 2056, Weber 40's, carb cam, pertronix Ignitor, Crane HI-6 with PS91 coil, stock 74 distributor with the advance plumbed to the carbs.
28 mm Venturies
.45 idle jets
120 mains
F11 emulsion tubes
200 air correction jets.
Harvey

Kevin Powers · 10-13-2002, 01:50 PM

this is when the whole carb "theory/reality" starts. harvey is down across the board including the ac and the mains. not just the idle jets. while the changes scream go lean, they are pretty subtle. harvey have you ever had your engine on a exhaust analyzer (sp)? if so what air/fuel ratio did you wind up with?

kevin

scg · 06:21 PM

...and yet another set of numbers (28/4.5/120/F11/200/50/50/55)

It's an art.

A weber voodoo doll helps too (tuning webers).

campbellcj · 10-13-2002, 07:25 PM

I have no idea what's in my 44IDF's. About the only thing the PO didn't provide with the car was the carb jetting (his wrench rebuilt & set up the carbs and didn't write down the jetting details). All I know is the idle jets are 50's.

Having nothing to compare it to, it seems to run quite well. I guess I'm lucky. I get some popping/spitting once in a while, like in cold running when I shut the throttles suddenly, but it's very minor.