Since having my cambelt replaced last week I've had a weird problem. At pretty much exactly 5000 rpm and WOT I get a stumble. As soon as it passes 5k it's fine all the way up to the redline. It doesn't seem to do it at part throttle either although I can't say this for certain.

The weird thing is it only seems to do this the first couple of times I pass 5000rpm. Once it's had its stumble it's fine for the rest of the drive.

Timing is at 14btdc, Bipes is pulling 8 degrees (from memory, it hasn't changed since before I had the belt replaced anyway). Turbo is at 6psi. Fuelling is via Vortech (again this hasn't changed since the cambelt) and stock pump, 1.6 injectors. My BOV is Turbosmart type 1 VTA, which seems fine.

I've checked for vacuum leaks but it all seems OK. It feels like a fuelling issue, almost like you hit a soft rev limiter although given that the only thing that has changed since the cambelt was replaced is the timing I suspect it may be that, even though I checked it and reset it to 14. It's possible the garage fiddled with the Bipes I suppose, I'll have to check that.

Any ideas?