1998 GS carb problem?

[dolmandabean]

Hi all, recently bought a 1998 GS500E And it's been running ok. Had the fairly common cam "knocking noise" and idle has never been overly steady.

I decided to try balancing the carbs after cleaning them (bike ran fine after cleaning, but felt like it was vibrating a little, hence trying to sync them) So i got the bike warm, set the idle to around 1750rpm, turned the bike off and removed the fuel tank. connected the sync tool (don't remember what it's called) and it wasn't overly off so i just turned the adjustment screw a little until the level seemed about perfect. Then 2 seconds later, the revs dropped off and the bike stalled out.

Now it refuses to start entirely. UNLESS i almost completely cover the air filter opening, in which case it will start, rev up to around 7-8k, then die as soon as its uncovered. Would normally mean the bike is running lean, right? but it doesn't explain why the problem was caused by balancing the carbs?

Anyway, just to be sure, i took the carbs apart and re-cleaned them in case the jets were blocked or something but all seemed ok and it's still only working at all with the air filter covered.

Any help/suggestions would be much appreciated!