Pic is on a 2007 ZX14. My profile a bit outta date.
Then I would say you have a valve running very hot. Low compression would affect both and not much chance of one going cold. Compression and leakdown test may tell you something.
Valve clearance has 2 functions; the first, everyone knows, which is to assure the valve closes completely to facilitate compression.
The second is to cool the valve. The amount of clearance (duration from contact to contact of the cam lobe) determines the amount of time the valve spends on the seat. Too short a duration, no chance to transfer heat. Too much duration and heat
actually passes back into the valve seat and the valve head.
It may be a pig, but it's a pig with a rocket in it's ass!
Last edited by Hammerhead; 07-18-2019 at 03:58 PM.
Other than clearance, the number one cause of burnt exhaust valves is a sacked out valve spring. There is surprisingly little seat pressure on these bikes, like 28 pounds or so, so, ther isn't much margin for error if one starts to get soft.