Hey guys, I have just joined after perusing your forum for many answers over the last couple of months. Love the forum and the great advice going on here!

I have recently inherited a 'recently running' 1983 XS250 special, to add to my collection of not yet running XS's. It's the DOHC YICS model.

I started with the usual stuff, ultrasonic cleaned the carbs, inline filter, new plugs, new oil. It WILL NOT START. unless I spray it with 'start ya bastard' an ether spray, then it fires instantly, I have to keep the idle speed at 2000+ RPM and it will run all day, as soon as I let go of the throttle, she dies. Even when warm, it won't start again until I spray it again and then it starts straight away. Any ideas?

Go back to the carbs, if 'start ya bastard' gets it going you got/there is something wrong in the choke/idle circuit.

Yep Cynic is right if "start yer bastard" makes it run then you definitely have a blockage.

 Strip them carbs ,and get the pilots out ,

I used to own an xs250 with the very same symptoms. I eventually sorted it, well my sanity, by using "Burn ya bastard"

the carb orifices are very small on these bikes and gum up too easily. thorough cleaning with ultrasonics and air should get them serviceable. you might even need to do it twice!!

Thanks for the replies guys! So I had another look at the idle circuit and some silly monkey (probably me) had the air pilots screwed all the way down. It still doesn't start immediately. Sporadically it does, but then it revvs to high heaven (5-7k rpm) and hangs there. I'm absolutely scratching my head on this one.

sounds like an Air leak,  

 

Check float levels