Long story--. Got the bike a year ago (Australia). In the first couple of rides it felt like it was running out of gas,stopped for a while (I didnt think it was near empty). Put it on reserve, it started and went away just fine. Pulled into the servo and filled it . Only took about 9 litres so not really near needing reserve. Problem seemed to go away. Since then I usually get 220 ks from tank before reserve. ( Only thing I did was change oil and plugs). For a year it went perfectly. Revved out well, never felt like it was faltering. Then the other day (it was raining ?) it again felt flat, like it was in limp home mode, wouldnt rev above about 6000, just like a year ago. Then it felt like it was going to conk out. So I turned to reserve and it picked up to normal revs and away I went as normal. Got to a servo and filled it. Only took 9 liters-- plenty of gas left. What's going on. Its not low on gas ,despite picking up after switching to reserve. Does kind of feel like limp home mode, I think, but its been running beautifully for a year before this incident. Tank breather seems clear. Vacuum line from fuel tap seems fine. Tank itself and petcock mesh towers were clean as a whistle when I checked a while ago. Dont know if its been de-restricted or not but its been running fine for ages before this. Speedo hasnt been mucked around with recently. Any ideas, boys??

Sounds like a fuel flow problem. As you say going to reserve cures the problem, some type of fuel tap fault and changing from main to reserve clears it. Can only suggest you check the fuel tap may be some sort of diaphragm problem.

A speed sensor fault that activated the 5500 rpm limiter would not cause the engine to conk out, it would continue to run as normal up to 5500 rpm.

Try giving the carbs a good clean out, mine was doing similar and had s look the air filter looked like it had never been changed and when I got the carbs they was a bit mankey aswell but after a good clean I never had the problem again

Excuse the punctuation this smart phone is trying to make me look dumb

It does sound like an issue with your fuel tap, they're known to cause the occasional running problem on some bikes.

If you open up the tap you might not be able to see the cause, particularly if the problem is intermittent.

Rick Oliver sells a tap rebuild kit which might be good insurance.