The carb bodies had unfamiliar ID numbers stamped on them so I did a bit of investigation work as to their original fitment. It seems they were originally fitted to a Rotax snowmobile engine and had been converted to run on the customers TZ350. I happened to mention to the customer after we'd done the work that they were ex snowmobile carbs and he should check that the needle valves (float valves) were of the correct flow rate, as the snowmobiles have a fuel pump and are fitted with low flow rate valves. These valves will not provide enough fuel for a gravity fed race bike.
He came back to me and told me the valves were #3.0. The correct Yamaha valves are #3.5 with 6 outlet holes.
This he said, explained why all of last season the bike would run lean and misfire on the straights.
I supplied him with a pair of the correct #3.5 OEM spec valves which should cure the problem.
He declined the offer for me to build the carbs for him, so who knows what other incorrect parts are fitted...
Yamaha OEM needle valve part number 23X-14107-35-00
£24.95 each in stock