Giving Up On Vacuum Advance Options

[Ansbacher]

Car = '74 2.0 Liter, Dual Dellorto Carbs

For years I have been 'adequately" running an 009 mechanical only distributor. Finally took the pervasive advice out there to go with a vacuum advance dizzy from a 1.8L 914. Since only one of my Dellorto carbs had an existing vacuum port (ported type), I had to drill a port in my other one (no problem there). I used good quality anti-pulse valves in the lines and measured a maximum vacuum of 12 inches of mercury with partial throttle.

Installed the 1.8 dizzy and set the timing, first without the vacuum lines attached. To satisfy my usual 30-32 degrees at 3500 RPM, the idle timing had to be at about 5-6 degrees (quite low for my setup which is happier at about 10 degrees. When I attached the vacuum lines my timing at 3500 RPM went sky high into the 40s. This seems way too high. Is this normal? Overall, I found the car to run better without the vacuum attached and the carbs plugged off.

Am I doing something wrong here? I don't like the numbers I am getting. Everyone said this was the way to go with carbs, but I am not seeing results. Advice appreciated.

Ansbacher

[72hardtop]

You can garner a lot from that thread with the first 20 pages alone.

Remember....

Get above 14:0 - 15:5 on the progression circuit and below it (14:0 - 15:5) when on the main jets. Ideally when under load/WOT... 12:5-13:2 or so. 14:0 -15:5 is the highest area for EGT's.

Load = Throttle position

No lean tune cruising with mechanical only distributors.

[tmessenger]

72hardtop

Sounds like we have very similar engine builds, mine is:

Fat Performance built 2056 long block, 42x38 ported and polished heads, Fat 442 cam, 8.3 : 1 compression 4k miles on the build.

I just bought this car 6 weeks ago so am just now starting with the carb tune. The current configuration I inherited :

40 IDF Webers, 32mm venturi's, 60 idle jets, 135 mains, F11 emulsion tubes, 175 air's, SVDA distributor with stock 2.0 heat exchanges and Triad muffler.

I've just ordered an A/F gauge to start the process.

Can you tell me how your finalized carbs jetting came out and your A/F readings? Could be useful to both of us to compare notes.

Thanks, Tim

You can garner a lot from that thread with the first 20 pages alone.

Remember....

Get above 14:0 - 15:5 on the progression circuit and below it (14:0 - 15:5) when on the main jets. Ideally when under load/WOT... 12:5-13:2 or so. 14:0 -15:5 is the highest area for EGT's.

Load = Throttle position

No lean tune cruising with mechanical only distributors.

[72hardtop]

72hardtop

Sounds like we have very similar engine builds, mine is:

Fat Performance built 2056 long block, 42x38 ported and polished heads, Fat 442 cam, 8.3 : 1 compression 4k miles on the build.

I just bought this car 6 weeks ago so am just now starting with the carb tune. The current configuration I inherited :

40 IDF Webers, 32mm venturi's, 60 idle jets, 135 mains, F11 emulsion tubes, 175 air's, SVDA distributor with stock 2.0 heat exchanges and Triad muffler.

I've just ordered an A/F gauge to start the process.

Can you tell me how your finalized carbs jetting came out and your A/F readings? Could be useful to both of us to compare notes.

Thanks, Tim

You can garner a lot from that thread with the first 20 pages alone.

Remember....

Get above 14:0 - 15:5 on the progression circuit and below it (14:0 - 15:5) when on the main jets. Ideally when under load/WOT... 12:5-13:2 or so. 14:0 -15:5 is the highest area for EGT's.

Load = Throttle position

No lean tune cruising with mechanical only distributors.

Final jetting on mine....

47.5 idles
125 mains
210 air correctors
F11 Tubes
28mm vents

At light/part throttle the AFR hovers 14.X - low 17.X (light load conditions)

WOT - 12.X - low 13's

Timing is 28 BTDC @ 3200rpm's (hose off/plugged) SVDA

Elevation here is roughly 525 feet above sea level