Venturi size is a compromise; to get good torque at low engine revs you need a small diameter to maintain air speed through the venturi. As the revs increase there is a limit on how much air can get through and eventually the motor will run out of puff. To maximise torque at high engine revs (this = power as torque x revs = power) a bigger venturi is required. If you want gains at one end you'll lose it somewhere else.
Yamaha sidestepped this problem on the V Max with V Boost. The carbs gave good torque at low and mid engines speed but were not sufficient to give good top end power. To overcome this they inserted a butterfly between two carbs that opened as the revs rise thus allowing sufficient mixture to satisfy the motors requirements.
As Pete says, size matters (not that I would admit that to my wife
).
The 38's have a 41% larger throat area than the 32's and are 24% larger than the 34's.
Why is that important?
You need to consider how a venturi works.
As the throat narrows the air has to speed up to get through and this reduces the pressure.
It is this lowering of pressure that draws the fuel through the jets.
The faster you draw the fuel through the better the atomisation and the better that is the better the mixture burns and the better the mixture burns the better the bang.
On that basis if you have a bigger venturi there is a smaller pressure drop which results in poorer atomisation = poor running.
Now, to speculate, your issue may not be how much fuel you are getting but how it is being atomised.
If there are big droplets and these are pooling in the inlet they will evaporate and add to what is passing into the cylinder causing the idle to hang.