I just installed an air/fuel gauge on my new 2110 engine.
It has Weber 42 DCNF carbs with 34 venturis, 60 idle, 140 main and 180 air jets.
At a steady 3300 to 3500 rpm the air fuel ratio is about 11.3.
I first thought this is because the idle jets are too big but probably the main jets are functioning at this rpm.
Do you think I should try bigger air jets to lean things out?
Thanks.
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I think I would try some 130 mains first. Suggestion.....only change one thing at a time and then road test. How rich is it under 2500 ?.......Bruce
A few assumptions I've been laboring under - maybe folklore, maybe not, but this should help get the discussion rolling:
- Whether you're on the main circuit or not is more a function of throttle position than revs. So, if you're in a situation where you don't have to give it much boot to hold 3000-3500, you may very well still be on the idle circuit or maybe just starting into transition. It depends on factors such as grade, gearing, headwind, etc. On a level road, I can usually hold 3000 rpm with just a little throttle, so I'm mainly on the idle circuits.
- I think most people with carb size and displacement around yours start with 135 mains and 200 air jets, and then season to taste. That's where I ended up staying with my 2024cc (same 90.5 jugs as you, but 78.8 stroke instead of your 82). I have IDF 40's with 32 chokes.
Mitch, I have been thinking my idle jets are too big at 60. Aircooled.net website suggests 52-55 idle, 140 main and 180 air. These suggestion are based on venturi size.
Since I have 42's with 34 venturis maybe my mains should be a little bigger than yours.
Thanks Mitch and Bruce for your replies.
Michael, if you haven't already read this, it's a great place to start before monkeying.
Mark Harney may not have written THE book about tuning Weber carbs, but then again, he may have.
