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Tue May 17, 2011 8:16 am

I've hooked up an original judson boost gauge to my 36 hp Judson engine. The Vac / Pressure needle appears to move through its range of motion correctly and is reading accurately.

When the engine is at an idle the white needle doesn't hold steady. It flutters back and forth approx 1/8 of an inch in the 3-4 rage on the vac side.

I checked my vacuum line from the back of the gauge to the inlet at the bottom of the blower. No leaks found in this line.

Is this movement of the needle at an idle normal?

Tue May 17, 2011 10:05 am

52brezelfenster wrote: When the engine is at an idle the white needle doesn't hold steady. It flutters back and forth approx 1/8 of an inch in the 3-4 rage on the vac side.

Hmmm...at idle your gauge should be reading between 17 - 23" mercury:

Quote: At idle the supercharger gauge should indicate 17" to 23" of vacuum depending on the engine. A drop in vacuum indicates improper valve clearance, rings need replacement or there is a leak in the induction system (a blown gasket or a cracked manifold).

Tue May 17, 2011 10:10 am

Hmm :?:

Engine is a strong runner. Time to re-check connections and fittings.

Tue May 17, 2011 10:14 am

John, is this what it should do at idle as during a rev? Dan posted this on youtube.

Tue May 17, 2011 10:19 am

52brezelfenster wrote: John, is this what it should do at idle as during a rev? Dan posted this on youtube.

Yes...that's how mine worked.

Sat May 21, 2011 8:04 pm

Got this handled, idling vacuum is now reading about 17-18. Very small vacuum leak was thowing things off. Installed some new hose clamps, some new flex line for preventative measure, all set to go!