Cold start issues after carb rebuild

Hello All, I have recently picked up on a project that has been sitting for over a year - '90 FJ/XJ 600. I have cleaned the carbs in ultrasonic bath, checked fuel valves, set the float level according to the manual. The bike is running stock air box, and right now the only way to start it when it is cold is by using starting fluid. The bike starts, revs up, sometimes dies after 5-10 seconds. After 3-4 attempts it starts up and runs a bit rough ( carbs haven't been synced yet). After 10-15 min when it warms up, I can stop the engine and it will start without a problem. On the next morning however, I need to play with the starter fluid again.

Thing to consider - I have replaced the OEM 4in1 exhaust to a custom 2in1 manifold and muflers.

I am not a mechanic, more like a hobbyst, I can do most of the maintenance myself , perform some repairs but carbs and fuel related issues are my cryptonite I would be really greatful for any tips and suggestions how to proceed.

 

I think you need to revisit the carbs. Sounds to me like the enrichment circuit (choke) needs attention and probably the pilot circuit. I also suggest that after removing all the jets, emulsion tubes and pilot screws you boil the carbs for about 10 minutes and immediately blow then out with carb cleaner followed by air. The boiling water dissolves all the gum and the carb cleaner blows it out, and the air clears all the passages.

 

The holes in the jets for the pilot circuit are VERY small, its likely putting them in the ultrasonic cleaner for as long as you did wasnt enough to unclear them. I would take the carbs back apart, take everything apart, jets, emulsion tube, idle mix screws, ect, out of the carb and blow it all through manually with carb cleaner. On my 700 maxim x, even with the small pilot jet hole, I could see a pin hole of light through it once it was clear. With that in mind, check all of the small holes to make sure they arn't plugged.