No I have not flow tested the OEM Mikuni BS40 carb.
I have included below some information I have gathered over a considerable amount of time on the internet doing research in this area.
Keep in mind that Mikuni does NOT provide airflow numbers for their carbs (Ever wonder why ?)
Calculate Carb CFM needed for a given engine size
Required Intake CFM for an given engine size
Volumetric Efficiancy (VE) is affected by intake type, camshaft grind and type, boost, and many other factors.
Here are some guidelines.
Factory engine: 65%-75%
Mild street performance, flat-tappet cam: 80% - 83%
Mild street performance, roller cam: 90% - 93%
All-out race engine, 95%-105%
Blown engines, typically over 100% or higher, depending on amount of boost.
Instructions
1) Find the displacement of your engine in cubic inches (CID). Determine the maximum RPM for your car. For example you may have 450 CID with a maximum RPM of 5,000.
2) Check the volumetric efficiency (VE) of your engine. If you don't know, you can assume that it's about 80 percent since most street cars are designed to that level of efficiency.
3) Multiply the CID by the maximum RPM and divide that product by the product of 3,456 and the VE. For example you would multiply 450 by 5,000 to get 2,250,000 and then multiply 3,456 by 80 percent to get 2,764.8. Then divide 2,250,00 by 2,764.8 to get the CFM required: 813.8.
4) Select a carburetor that will produce 110 percent to 120 percent of the required CFM. For example with a required CFM of 813.8 you would select a carburetor that can produce between 895 and 975 CFM.
Another formula to use is: CID x RPM Divided by 3456 = CFM
Suzuki Savage Engine:
652cc - 40 ci
VE - 75% - performance cam - 80%
Engine redline - 6500 RPM
Required CFM: Stock engine: 62 to 79 cfm (calculated)
Required CFM: Performance modified engine: 66 to 84 cfm (calculated)
http://www.carburetion.com/calc.aspAprox Approximately 71 CFM Needed for a 40 CID Mildly Built Engine
36 Centimeters (cm) = 14.173228346457 Inches (in)
A Mikuni 36mm carb flows approximately 120 CFM.
Carb CFM calculators
http://www.csgnetwork.com/cfmcalc.htmlhttp://speedmaster79.com/tools/carburetor-size-needed/http://www.bleachburnout.com/blog/2008/10/17/carburetor-cfm-calculator-with-g...http://www.4secondsflat.com/Carb_CFM_Calculator.htmlMikuni Carb size (IN CFM)
34mm MIKUNI Carburetor 109 CFM
35mm MIKUNI Carburetor 114 CFM
36mm MIKUNI Carburetor 119 CFM
38mm MIKUNI Carburetor 129 CFM
40mm Mikuni Carburetor 140 CFM