Recently my track bike that I use at the Chiang Mai velodrome has developed a problem in that as I rotate the pedals, the chain is very taut at one point and incredibly slack at another. I've checked the chain (1/8th) for wear and that's ok; The chainring is a newish Campagnolo Pista 52-tooth and seems perfectly ok; the frame is inline (check in a decent bike shop) so I am at a loss ..... The main problem it causes is when really winding it up, I get harsh noises and the fear that the chain will jump off. Any help available?

Check bottom bracket it's possibly loose or worn.

_________________
I never took drugs to improve my performance at any time. I will be willing to stick my finger into a polygraph test if anyone with big media pull wants to take issue. If you buy a signed poster now it will not be tarnished later. --Graeme Obree

Your chainring could be out of round. try another chainring and see if you still have that issue..

_________________
Flickr
Tarmac SL3 Project Yellow
Follow on Instagram

Sheldon has advice on centering chainwheels on fixed gears....
http://sheldonbrown.com/fixed.html

In addition to the above, check the cogs at rear and every single link in the chain to see if one has binded.

_________________
"Physiology is all just propaganda and lies... all waiting to be disproven by the next study."
"I'm not a real doctor; But I am a real worm; I am an actual worm." - TMBG

Thanks for your help. I had a new 50-tooth Stronglight chainring and that seems to have been the problem. After flaffing about for an hour I changed the chainring for an old-style Campagnolo 51 -tooth and what do you know? Perfection. Thanks for your help guys.

Your problem is sorted.
Chain wear is usually uneven and is also the culprit. Possibly the worst thing about track bikes is the drivetrain and having it remain correct.