Weber 46 + 3L + RSR style cams

[H-viken]

Hi

Any thoughts on how the Weber 46 carbs should be set up for a 3L engine with RSR style cams?

We have run in to an issue where it runs rich below 4,000 rpm but nicely above.

Johan

Short video from first dyno day: https://m.youtube.com/watch?v=tT18K1XqvkY

[1QuickS]

Idle air correction jets are 0.80 mm for 46mm Webers. Changing them to be larger will lean out transition richness without decreasing idle fuel jet size. A smaller idle fuel jet will lean out mixture from idle through transition.

Actually, idle circuit is active through 5000+ RPM but weaker as RPMs rise.

Venturis can be 38mm through 42mm so main jets will change accordingly.

My customers that tuned using both dyno time and street driving time to optimize transition tended to use 60 idle fuel jets and 90 or 100 idle air correction jets. There is an easy modification that will allow changing idle air correction jet size.

Idle air correction jet adjusts fuel emulsification in a fashion very similar to how the main air correction jet affects fuel emulsification as RPM increases.

Emulsion tubes can be F3, F7 (same as F3 except has richer top end) or F24. Jetting is dependent upon venturi size and emulsion tube selection plus what type of exhaust is used. F3 and F7 emulsion tubes activate the main circuit more quickly than the F24 emulsion tubes which could create a transition richness issue.

WOT from low RPM for dyno run is what I assume you are trying to resolve, partial throttle for cruise will be a somewhat different issue.

What are the particulars of your current setup? Such as: venturis, auxiliary venturis (tall or short), emulsion tubes, exhaust type (muffler for street use is what video shows).

With a twin pipe exhaust you can expect 300 HP with the following setup:

• 38mm main venturis
• 155 main fuel jets
• F3 emulsion tubes
• 155 main air correction jets
• 60 idle fuel jets
• 100 idle air correction jets

I can provide alternate jetting configurations using different emulsion tubes and main venturis but the above is representative of the alternates.

[H-viken]

Thanks for responding Paul, really appreciate it!

I’ll find out exactly what we have at the moment, but I believe we are using F3 emulsion tubes and 195 main Jets. We started with 175 and it was too lean up top.

We built the exhaust ourselves. Headers are equal length with 1 3/4” primaries, going in to 2 1/2”, finally merging in to a one-out at 3”. Collectors are from Burns and we use two shorter mufflers in sequence, which are straight through (perforated tubes).

The dyno we use is conservative and we are seeing 305hp at 7,170 rpm and 320nm of torque, with a very flat curve.