Whistling Griff 500

[AHOUSE]

The engine on my 96N Griff has developed a shrill high pitched whistle. This tends to start after accelerating hard and then comes back whenever foot taken off gas. It seems to be coming from the plenum chamber but not 100% sure. I've been told it might be the stepper motor but this has been checked out and is ok. Has anyone else experienced this/any suggestions as to what might be problem?? (Based in N Yorks).

[joospeed]

are you handy with the spanners? .. I've come across this before and it's usually 1 of 2 things .. either too high an airflow on the idle bypass allen screw or - took a time to isolate the other but it's usually a loose inlet manifold .. the bolts under the plenum come loose and under decel the high vacuum causes a high pitch noise as the air rushes in. If it's been doing it a while it's best to change the valley gasket and sort it properly once and for all although you might get away with just tightening the bolts down.
Joolz

[2 Sheds]

yep agree with Joolz, sounds like an air leak, spray some solvent / cleaning fluid around the suspected areas whilst idling and if the revs rise you've found the leak,
Tim

[AHOUSE]

Thank you for swift response.
As I tend to cause more problems when get spanners out I may be getting in touch (Joolz - it's the Crimson Griff that followed you up A19 on the very wet karting day in Boro last month.)

[simpo one]

I'd guess inlet manifold - exactly what happened to my BMW when the crankcase breather valve stuck. Lumpy idle and white smoke from exhaust on start-up too.

[House]

Just for future reference...it was loose inlet manifold bolts under plenum chamber which had enlarged boltholes in gasket. 10/10 for diagnosis chaps.