Your question reminds me of the KDX 220,its a great trail bike but under carburated,so serious riders bore the carb out bigger for more power!What Im getting at is wouldnt a fly wheel weight,and a Moose spacer be a better choice?I run my KX500 on fast wide open fire roads to the tightest single track you can imagine with only a V-Force reed as my only engine mod and it handles the tight stuff well,I will try the fly wheel weight in the future as every one who has in the woods loves it and its cheaper than a new carb.If you arent worried about max power and top end and only ride in tight woods and want to try a smaller carb Id only go to the nekt smaller size,you will get better gas milage,low end will be more tractor like, but top end will suffer.Sorry I dont have any info on the type of carb you want,at one time I think it was Krause Racing made a kit that bored out your stock carb,then they had differant size venturie sleeves you put in to make your carb larger or smaller and was cheaper than a new carb,hope I helped a little.