The carbs on my CB500 receive gas via shared fuellines and T-joints, knowing: carb 1+2 share one supply route and carb 3+4 another. The tubes have different lengths, so simply draining the four carbs will not give accurate results for comparison: when drained, two carbs will give extra fuel, knowing all the fuel that is in the shared supply line. Here is a method to have 'clean' results.
Have the bike on the center stand.
A) Open petcock. Give it time to be sure all bowls will be full and the float valves are shut. Close petcock.
B) Drain carb 1 and carb 4. You may as well pour that gas in the tank. Close drainscrews.
C) Now drain carb 2, save that gas in a labeled glass. Idem for carb 3. Close drainscrews.
D) Open petcock again to allow all bowls to refill and the float valves to shut off again. Close petcock.
E) Drain carb 2 and carb 3. You may as well pour that gas in the tank. Close drainscrews.
F) Now drain carb 1 and save that gas in a similar glass as in step C). Idem for carb 4. Close drainscrews.
G) Position all glasses next to one another and compare the levels (see pic below).
I have done this test myself last weekend. All carbs showed the same amount of fuel: 50 ml exactly. Not having tampered with the floats ever and as all four carbs show the same quantity, I trust this result is how it should be. I'm confident my results go for all oldstyle carbs on the CB500 and CB550, as they share a same factory set float level of 22 mm. These carbs are numbered: 627B, 649A, 022A, 087A and 069A.
It is a simple test. No need to disassemble anything, no need to improvise a testtube. You do not even need four glasses. The second pic shows all you need. From left to right: gloves, any old used tin that will fit nicely under a carbbowl to collect the drained fuel and a measuring glass. That's all.
