If you can, fit a boost gauge to the "spare" / blanked port on the back of the inlet manifold.
Assuming you're not burning oil (are you loosing oil) then it's a fuel air ratio issue.
If you're not seeing enough air at the manifold when under...
Hi everyone,
Sorry for the slow update - I was busy getting married (of course, the One-Ten was the wedding car). I’ve since sorted out the thermostat (it was stuck open) which made a bit of difference. However, I’ve now done about 1500 miles...