My first check would be the fuel lines. The CB500/550 is very sensitive to correct fuel line routing. Fuelline to the T-joint of carbs 1+2 should have a length of 17 cm with an ideal internal ⌀ of 5,5 mm. The line to 3+4 should measure 28cm. However, if you happen to have the old model fuelcock (with the bowl), fuel lines lengths are 18 and 30 cm respectively. Outside ⌀ will be around 10 mm. With the correct dimensions there's no chance of kinking. Abstain from inline fuel filters. They'll cause irregularities in fuelflow on a CB500/550.