what causes this knock?

[Dxc545]

So I made a good long 3rd gear pull through the rpm's and right at 5 grand I get a spike of knock which stays there. My timing is pretty low around 8-9 degrees and boost is around 18 psi. Could it be fuel related? I haven't bought a afpr for my walbro 190. Any thoughts?

 

[gofer]

It's your timing advance, that's actually pretty aggressive for 91oct. Your AFR's look good, just pull 2* of timing at 4.5k and 1* at 5k, then bring it back and see if the knock disappears...