Might be worth checking the plugs-

High revs can cause spark plugs to have there spark blown out if the gap is too wide.

Checked the gap... Is 0.8 too wide for a 5k?

0.8MM is the standard gap size for all the K series motors with points dizzys. The ones with electronic dizzies and dished pistons ran 1.1mm gaps with long reach plugs standard.

 

If your coil isn't up to the task it could be breaking down. A spark tester is an excellent tool (worth about $25 on ebay) to keep in your toolbox, I've got one like this:

 

Edited August 26, 200917 yr by Felix

Well.. What seemed to work was hacking up my exhaust gaskets so they weren't too small (ported head) and also causing an exhaust leak because the gaskets

aren't really doing their job properly anymore (fell apart because of the excess handling while grinding them out). Goes pretty fast now :y:

Edited August 27, 200917 yr by seabiscuit

interesting think u should find a gasket which will suit now to get rid of leaks !