Calculating carb size and main jet sizeing for new carbs

[davybondo]

I just found this Video I thought it has good info and makes sense to me

youtu.be/uZMgEcnnRGE

also found this from a guy on Moped Army

I hope it's ok to quote this guy

Bill Mazzacane /
wmazz
Nov 16, 2016 01:15AM

Your problem is the carb is just too large in diameter. Why do people keep making the mistake of thinking that bigger diameter carbs, must make higher top speed.

If you want mediocre performance in trade for possibly small gains, keep working.

You need to start by learning the basics of jetting. A 100 main + a 32 low = 132 fuel units. almost any arrangement that equals 132 will work.

Always start with the low jet. Start jetting it richer 35 to 40. then open the air screw, and drop the needle. If you settled on a 37 low, start with a 95 high.

Jetting always, always starts on the bottom and works up. Adjust the carb to work well at low rpm ~3000, then drop the needle ~4500 rpm and move to the mains

The lows are always flowing fuel, so changes to mains include the low jet. That is why you start at the bottom.

You will have better luck using this technique with your 17mm carb, it will get gains in low end acceleration and peak HP.

[Lucass2T]

Dellorto has a graph to pick the right carb size. It's actually quite accurate.
www.ducatimeccanica.com/dellorto_guide/fig8.jpg

It links venturi diameter to power output and doesn't bother with engine size. That sounds weird at first but makes sense when you think about it.

It's the ammount of fuel a motor needs that determines the carb size. A small and super efficient race prepped motor can process/consume as much fuel as a streetbike with double the engine size but similar power.