Fluttering Vacuum Gauge Reading

[66 Sat]

Hi, I bought a vacuum gauge to help tune my new carburetor. Connected it up and it is reading 18inhg which I thought was good, but the needle is fluttering very quickly. Stays on the 18 reading but isn't steady.
From my research this is pointing to worn valve guides. Car has no symptoms of anything wrong, no smoke, no oil usage, engine was rebuilt probably 4 years ago by a reputable shop.
Any other possible causes for this (dodgy gauge?), or other tests I can perform to determine what's going on?
I really don't fancy pulling the heads to get it fixed. Engine is a 318 poly, stroked to 354.
Thanks for any advice.

 

[493 Mike]

Hi, I bought a vacuum gauge to help tune my new carburetor. Connected it up and it is reading 18inhg which I thought was good, but the needle is fluttering very quickly. Stays on the 18 reading but isn't steady.
From my research this is pointing to worn valve guides. Car has no symptoms of anything wrong, no smoke, no oil usage, engine was rebuilt probably 4 years ago by a reputable shop.
Any other possible causes for this (dodgy gauge?), or other tests I can perform to determine what's going on?
I really don't fancy pulling the heads to get it fixed. Engine is a 318 poly, stroked to 354.
Thanks for any advice.

Is the valve lash correct?
Mike

 

[66 Sat]

Yes, checked them a few thousand miles ago when I had an adjuster come loose.

 

[HALIFAXHOPS]

 

[66 Sat]

I've got the rapid needle vibration but the movement is very minimal, maybe 1inhg on the gauge.
What tests should I do to confirm the worn valve guides?

 

[Rebelrouser]

I've got the rapid needle vibration but the movement is very minimal, maybe 1inhg on the gauge.
What tests should I do to confirm the worn valve guides?

using a vacuum gauge to diagnose worn valve guides is pretty hard. A guide has to be loose enough to cause the valve to rock on the seat. So you should be seeing oil smoke when you start it if the guides are loose.
Fluctuations in the needle indicate a valve not sealing, or opening properly. So worn camshaft lobe, weak or broken valvespring, burnt valve etc. with the small movement you describe the problem is just starting so next step is to use a compression gauge and isolate to what cylinder is got a problem.

 

[pnora]

I've got the rapid needle vibration but the movement is very minimal, maybe 1inhg on the gauge.
What tests should I do to confirm the worn valve guides?

If thats all its fluctuating there is nothing to worry about. You are making a big deal out of nothing.

 

[66Newport]

You can use a reducer in the vac line to steady the needle.
Sounds like you're good though.