75 Twinspark whistle and no torque when accelerating

[Divano Veloce]

Hi All,

after a cylinder head freshen up my twinspark 75 has a whistle from about 2800 rpm onwards thats proportional to how open the throttle is (with a small delay). Its very much like the sound of the turbo on my wifes TDI however instead of being associated with lots of torque on the TDI there is very little torque/power

I have so-far done the following:
Manifold vacuum when warm at idle, on throttle and off throttle (18,0,22)
Replaced everything upstream of the throttle body including air flow meter, IAV and associated hoses.

Google says it might be a blocked exhaust but the manifold vacuum test doesn't support this.
It starts and idles well, good oil pressure and maintains temperature. Valve clearances and timing are good and head studs re-torqued.

Any ideas on what it could be or what else to test is appreciated

[Divano Veloce]

Problem solved.... it was a fiberglass furball lodged in the rear muffler.