Baffled

My fuel tap has 3 positions, on, prime and reserve and my fuel pump is electric and lcan hear it ticking when l try to start the bike. The bike ran well after l took your advice and re-cleaned the pilot jets. I then took it for an MOT and it cut out on the way but started when l set the fuel to prime. I left it on prime for the test and took it for a run afterwards turning the tap back to run. I did several miles and it ran well then stopped at the shops. After starting again the bike ran for a couple of hundred yards before cutting out again. Back on prime it started and l left on prime to get home. As l understand it, prime let's the fuel flow freely and run requires the vacuum from cylinder one to get the fuel to run although l don't know how this works. The vacuum tube seems in good condition (carb rubbers also look good), petrol pump seems to run but obviously something is not right. My battery is not good and won't start the bike after a limited number of attempts even when freshly charged so needs replacing. I suppose that could be a cause but l think l need to check the pump and vacuum to the fuel tap to fix the problem. Thank you all for your help.

FIXED The pilot jets looked clean but the very fine hole at the top was blocked so your analysis was spot on. Once cleaned the bike would start and accelerate. Knowing what the pilot jets do made all the difference. I still have some problems as it will sometimes cut out and I need to set the fuel to prime to get it to run so I think I have a fuel pump or vacuum issue but at least it will run now.

Thank you for your reply. I will look at the pilot jets again although what puzzled me was was how clean the carbs were, Mikuni by the way. I could see no sign of any dirt or build up of residue in the jets or anywhere else. I tested after cleaning with the airbox off and petrol fed by an extension feed so I could see what was happening. I'll clean again and try with the airbox back on. It was strange that the behaviour was exactly the same as it was before I stripped it down. I will let you know how it is after I put it back together. Thanks again.

My 600 Diversion with low miles will start on full choke and rev at 3000. However if I touch the accelerator it cuts out. I have cleaned carburetor jets (it was very clean anyway), put new fuel in but still the same problem. I have also run it with fuel tank off and can hear the pump run and see it take fuel from temporary feed. While it runs fine on full choke it will cut out when I put the choke in even when warm and does not seem to want to take any load Has anyone any suggestions as to what could be causing this problem? Everything I look at seems healthy so could it be some electronic problem? All help appreciated as I am baffled.