without the washer the spring will dig into the small o'ring, that will cause the pilot jet to change it's setting, the small o'ring is easy to miss because it gets bedded in and needs digging out of the blind hole..I have posted a few of these instructions on how I repair my carbs so one of them should be easy to find, unfortunately they were all replies to other questions so maybe not..but for the basics..
Buy the repair kits..
don't split the carbs if you don't want to rebalance them.
make sure the butterfly valves open and close at the same time.
check the diaphragms by gentle stretching for pin holes and splits and replace them if they are damaged.
when you replace the diaphragms use a small amount of silicon gasket gel to seat them properly in the grooves..
take photographs of each step so that you know how they go back together and you don't lose small parts..
use all the parts in the repair kits except the round o'rings that you would have used if you split the carbs.
clean all the jets and nooks and crannies with carb cleaner spray..
and don't forget the air cutoff valve..that's where the oval o'rings go..
Beauty is only skin deep but ugly goes right to the bone.