For the past year and a half i've been trying to figure out why my NC30 runs like trash...

The revs hang this can be very temperamental sometimes it takes minutes or seconds to return to idle (problem seems to worsen when the bike heats up). Also when I give a quick blip of the throttle the bike gasps for air and can sometimes cut out.

I have replaced the rubber boots / clamps, carbs have been ultrasonically cleaned and synced, new spark plugs, adjusted valves.

Any ideas? Really is driving me crazy, I've hit a brick wall.

Still sound to me theres a blockage in the idle circuit somewere. have you tried squirting wd40 or something through all the passages? Or maybe theres a tear in the carb diaphragms or something?

Does it settle a steady idle if left alone for a time.

Could the slide/slide rubber have cracks or tears in then? Or the slide hope is to big?

Another set of carbs from a known working bike would be handy in a situation like this.

Hanging revs is almost always the classic lean idle symptom.

Usuaully caused by poorly fitted carbs / bad sealing rubbers.

Problem with idle circuit

Mixture / pilot screws out.

Valve clearnaces / carb balance way off.

Does it change as the engine heats up?

Carbs are pain to fit, are they fully seated in their rubbers... i once went to have a look at an nc30 and the owner had put the carbs on and off like 20 times but wasn't sitting them in right.

Antoher one with similar issues was the balance was way off.

spraying carb clearn liberaller aroudn the rubbers when its hanging will help diagnose an air leak.

you also have carb balance screws / vaccum fuel tap take off hose... they can also leak air and cause above symptoms

Thanks guys for your advice.

Yes it seems to get worse once the bike heats up. Indeed could really do with some working carbs, just been offered 'meh' condition carbs for £110 which supposedly run well, debating weather to purchase.

Had the bike running with the tank off, noticed one diaphragm doesn't seem to be moving when revved?.. Shall check for tears etc next.