RD400F Main Jets

[Milan]

Thanks for the service data.
Have the floats at 21.5mm & thought i was good based on the 23mm.
So i will lower once carbs come off again

[SoCal250]

If it's running fine then there's not really a need to reinstall a intake crossover. It does help smooth out the the mid-range stumble if it's present. However, if you're looking to go 100% correct stock then go for it. It will have a very minor affect jetting.
Economy Cycle - Yamaha OEM Manifold Kit with Cross Over

If the 1A1 carb is set up the same (jets including air jet, slides, etc.) you should be good to go. I believe the bodies are identical, aside from the ID mark on them.

[Milan]

Ran bike a little yesterday.
Started up second kick.
Rode a little but not long .

Tried to start today , & could not get started.
Finally put the air screws in all the way.
Started & idled fine.

So looks like need to go up (2) pilot sizes to 30.
Would have never thought this.
Will try tomorrow.

Funny how it ran good the past 2 days & now not.
I will recheck cleanliness of carbs as well.
But new gas & new petcock installed.

M