Giving Up On Vacuum Advance Options

[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

[72hardtop]

Ported vacuum with vac port covered by the throttle plate at idle, connect in your vacuum gauge and check that you have no vac at idle.

Jake Raby likes to set up carbs at a/f 13:1 throughout so a bit different than the lean burn under light loads that John at aircooled.net aspires to.

Note: this is a heavy read.
The mother of all carb tuning threads (including timing theory) is on the samba here:

https://www.thesamba.com/vw/forum/viewtopic...c74c2cf44f55a21

Good luck,

Tim

Corrected. Got ahead of myself there. Ported vac always with a distributor vac advance.

Distributor on mine is fairly new (Bosch SVDA). Used an LM-2 for jetting.

Setting IDF's to 13:1 across the board would require reaming of idle jets. Standard Weber jets wont suffice. If I were shooting for power and coolness....13:1 would be where I'd want to be. But you won't see decent MPG's with that during part throttle condition.