DragBikeMike, I went with the Mikuni VM38 carb, but I don't get something. I thought it's better to ask here than to make a new thread. What do you do with the vacuum line from the petcock? And when running the motorcycle you have to put the petcock on PRI? Because I noticed there is no vacuum line on the VM38 carb

Hey Mike.  Incredible study here!!  I have a question that is in no way urgent or terribly important and I know it's the weekend, but I do want to pick your your big brain and put it out here to share!  If you could kindly respond when you get a moment I would greatly appreciate it.

I think you know I installed a PWK40 carb (knock off) on my bike (stock bike except for Jardine exhaust and air box cover removed).  The bike is running quite well, but I'm getting poor gas mileage (like 40mpg) virtually regardless of how aggressive I ride be it in suburbs or highway.  You may recall that I've rejetted several time and I'm running a #48 primary and #162 Main.  I think you commented those seemed really big and I agree, but I'm really not running too rich (performance-wise is good throughout, spark plug check, exhaust pipe check).

After seeing your test results and especially CFM stats, and learning about the venturi effect, fuel atomization, and more than my novice carb-tuning brain can handle....

My theory/question:  The PWK40 carb is just simply too big without any other engine mods (intake porting, cam, piston, valves, etc).  I think I'm having to "jet up" really big to mix up enough gas with all that air to get the correct air/fuel ratio.  I think I've basically force tuned a fat carb on the bike and gas mileage is showing the gluttonous appetite.

Your results for the Harley SS carb really got me thinking down this path.

Thanks in advance for your thoughts and expertise!!