My Secaii takes 5 minutes to start unless I pull airbox

Good afternoon everyone! My bike (1992 xj600 Secaii) has been reliable and started first or second crank no matter temp, elevation, and weather. Recently however, when starting, the bike stays at idle no matter where I position the throttle, sometimes I have to increase and decrease the throttle slightly to keep the engine running. Does this usually for about 5 or so minutes before revving up, at higher elevations itl sometimes spit out a little smoke cloud, but then run completely normally. I have not been able to recreate this phenomenon with the airbox pulled off, so I went ahead and replaced that, Carbs rebuilt all jets OEM. New air filter. Petcock is good. Fuel filter is new. I ordered a compression tester and am going to check the valves soon(later tonight after work or tomorrow), but any advise would be helpful as this is my daily vehicle. Thank you for your time!!

 

I have the same bike, don't really have any elevation changes to test that..... I have stock air box.
To fix the cold idle issue, I put in #20 idle jets, stock jets #15, but I really should have gone with #17.5. My screws are 1.5 turns out.
Why I went with #20, is because the manual list two types of carbs and idle jets, and I ordered the incorrect jets (#20).... they will work fine.
Had problems with the fuel hoses.... developed cracks, so sucking air to the fuel pump.
Bought an off the shelf fuel filter that looked like the original.... found it has a check valve in it that won't flow fuel very well, especially if you a have a cracked fuel line, lol. I'd check that all over, replace hoses as necessary, make sure fuel filter flows freely (blow through both ends).

 

I appreciate this. I'll do that tomorrow. Hoses should all be good as they're new but ye never know. I'll check the fuel filter too and make sure, never hurts to check. Jetting *shouldn't* be an issue as it's never had this problem in the entire 70-ish thousand miles I've put on it, but I'll try that and see what happens. If anything changes I'll keep you updated.

 

If your hoses are new, likely not a problem.... mine were 1992 vintage and due for replacement.
As for jetting, they were known to be very cold blooded, took forever to warm up when first started..... mine came with the stock #15 jets, carbs were clean, but the shop that serviced it had the screws backed out to 4 turns... with the #20 jets I'm at 1.5 turns, with the 17.5 jets I'd venture one would be around 2 turns. Mine only takes a minute or so to warm up to a normal idle, no choke.