GSXR-250/GJ72a Starting Issues

[Prosnorkulus]

Going fucking crazy here.
Picked up a 88 GSXR-250 a while back, was running sweet but was a bit sluggish to start ever since I had it, I knew it was a starter/ battery but was too lazy for ages to rectify the issue, eventually got around to swapping over starters with a known good one I had and at the same time put new plugs in while I was there.
Since then just cant get it to start, just turns over without firing, got it to fire and run for a bit but as I ran off to put my gear on it died and havent been able to get it to start again since, put in a new battery, checked that I was getting spark with new plugs, put new fuel through the whole system, checked compression, mechanical timing, timing light off the pick up, even went as far as to put in a new CDI.
Still nothing, Just wondering if anyone knows of some stupid little thing which causes these bikes to not run properly that Im overlooking?
Cheers in advance!

[Blabz]

Are you hearing it rumble when you're cranking it over?
If you haven't already, try spraying an aerosol like carb cleaner or 'start ya bastard' through the air intake whilst cranking, if so, did it sound like it was trying to fire?

If it's definitely got compression, spark and air, it could be that the carburetor is clogged and fuel isn't making it to the engine.
The pilot jets in the carbs on these bikes are as thin a single strand of electrical wire, so they can clog up if there's been stale fuel sitting in the carb.

It could be worth pulling the carbs off, removing the jets and soaking them in carb cleaner, and then clearing the jets out until you can see daylight through them (hold them up to the light and look through them)

Best of luck.