XR650 cutting in & out under full load full throttle

Hey Tech Buddies,
The XR pulls like mad through the gears but every now and again, like in the middle or late stage of over taking a car, in top gear the engine coughs for an instant before taking off again. It's not when you first crack the throttle on but at some point as it gathers revs toward the high range. Seems mainly to happen in top gear, like as it passes 100KM/h or more and is most noticeable under full throttle up hill. I ride mainly around Sea level and their is nothing on Bruny Island Higher than about 1,500ft. I am using Premium Unleaded either 95 or 98 RON, have drained the carby, checked the airbox/filter nothing obvious. I have owned the bike since new in 2000 and have only done 5,000KM on it and it has had no modifications. Any suggestions most welcome.
Thanks Heaps
Marc 

What does your spark plug look like?

 

Have you just drained the carbie or have you cleaned it really well ?
As that is not the same .

 

Let us know how it goes   

"I have owned the bike since new in 2000 and have only done 5,000KM on it and it has had no modifications"

There you go matey, that's your problem - ride it a bit more frequently?
5000km / 14 years = ...... umm, oh wait, eh (sweat), well, it is WAY less than what Mauser rides per weekend!
You see, using it is not abusing it - ride it!!!!   

Yep, drain the entire tank, not just the carb & replace with good fuel (can you get 98?).
New spark plug

Geez BigOne, that's not a very clever question to ask an Ozzi from London   
Let me do it for you: "Can you get 86?"


You see, he is on the opposite hemisphere, so you have to write the numbers upside down!
Bleddie Inglis, they lived too long on an island   







 

lol quite right!
Actually he's a Tazzy not an Ocker, so they may have to brew their own   

Did you check the float and float height?