From what I've been able to find, these likely came off an Alfa Romeo 33 1.3S. Engine size there seems promising given I'll be putting 'em on a GL1100.
The parts that came with it: 28mm Main Venturi, 3.5mm Auxiliary Venturi, #122/#145 Main Jets (idk why there's two different jets here unless these actually came from different cars), #F67 Emulsion Tubes, #190 Air Correctors, #100 Idle Jets, a SEALED Accelerator Pump Exhaust Jet hole, #33 press-in Accelerator Pump Jets. Other oddities are the idle mixture screw is 0.5 thread (according to TheSamba.com forum post), and the Main Venturi's are actually 44 IDF O.D.s (confirmed with David at Pierce Manifolds), there are 5 progression holes, each barrel has it's own vacuum port, and each carb has dual fuel barbs.
I'm tempted to give the existing setup a shot since most of the values besides idle jet are actually pretty close to Randakk's recommendations (fixing the mismatched main's of course). I'm not sure I understand the implications of my pump exhaust circuit being blocked off though, or the notably smaller pump jet.
Researching to figure out if I may in fact need major changes to jetting, I saw repeated references that make me question the recommended jetting, mostly the 28mm main venturi that comes with 40 IDF 70's.
The GL1100 is 271cc/cylinder. Basically any tuning manual for the Weber carbs will point you to larger main venturi's. For 271cc @ ~7000 rpm peak power, you'd land at around 31mm. Mark Harney of Harney's Carb Clinic suggests for high reving engines main vents should be around 2mm to 4mm smaller than intake valves, or 4mm to 6mm for torque. The GL1100 has 38mm intake valves. That would mean 36mm to 34mm for power, and 34mm to 32mm for torque. DVA Power references that ideal barrel size is 1.25xVent Size, so reversing that equation, a 40mm barrel would have an ideal venturi size of 32mm.
So, my oddity-level IDF's aside, why is it the go-to recommendation 28mm? Is it purely because the most common modern IDF is the 70 which has jetting close to Randakk's recommendations and he ran the trial-and-error on jetting, and swapping to say 32mm would be nearly $120 for vents alone and then changes almost every other jetting component as well?
Weber Main Vent Selection Chart:
- Weber Main Vent Chart.png (95.54 KiB) Viewed 1642 times
DVA Power Guide:
http://www.s262612653.websitehome.co.uk ... webers.htm
