40mm carb on a '80 cr390

I purchased a brand new 40mm round slide, the c&r500 air box grommet. I fabricated and modified the intake side adapting the 83 cr 500 grommet to the reed housing.
I changed the needle jet tube and carefully jetted the 40mm carb to the cr 390. You want to talk about the "hit" when you wick-it? What a wild ride it was.
Too bad I ended up selling it. The first guy who purchased it got injured on it. The 390cr was a fast bike anyway.

I wonder how the 40mm carb would work on a ported 250?

I built a '85 Honda 125cr I ported it and changed the port timing with the added roost boost increased voltage on the coil. She was beating the 250's but I couldn't keep it together. As I had more experience later on after we sold the bike it needed more fuel. It needed a 38mm carb. I realized this when I seen the 38mm carb on the 125 husky.
Porting, tuning, carburetor cfm/jetting along with the correct tuned pipe all goes together.

Just put a 38mm Lectron on the 390 ..... does it for me :-)