Tiger 955i Sucking In Air?

'01 Tiger 955i 84k one previous owner but needed plenty of tlc.
When I bought her 6 months ago, rode her home but kept 'popping back'. Fast forward 6 months, all suspension done, cam cover gasket done, inlet manifold gasket replaced with smear of hylomar, new upper & lower injector seals, vacuum pipes seem fine, new plugs & full service.
Still runs great but still pops back, if you spray brake cleaner towards the injector manifold on the left hand side, the revs rise slightly, indicating an air leak? I've changed all the normal culprits but she still pops back, consensus among fellow Tiger nuts is 'this is normal' but MOT guy thought there was a slight hesitation on the throttle, then he sprayed brake cleaner towards the inlet manifold, so it appears there's an air leak.

Those 'in the know' is there anywhere I've forgotten to look?

Appreciate your help.