Racor vacuum gauge

[William983]

I had the time to exercise my engines today after three months away. One of my racor gauges was fluctuating wildly.
Any thoughts as to why.? I have never noticed this happening before.

 

[FF]

Air Leak in fuel supply ?

 

[O C Diver]

When you write "fluctuating wildly", is there a dramatic increase in vacuum or decrease?

An increase in vacuum would most likely be a blockage either in the filter or somewhere from the tank to the check valve ball in the filter.

A decrease as previously mentioned, would likely occur from an air leak between the check valve ball (if it's sealing correctly) and the lift pump on the engine.


Increase or decrease?

Ted

 

[William983]

It was going from none to pegging out rapidly. Then back to none. Less than a second time interval. I’ll try to video it if it does it again tomorrow

 

[O C Diver]

What is the normal reading on the gauge? When was the last time the filter element was changed? Please post a picture looking into the bowl.

Ted

 

[William983]

This is what it started doing

 

[William983]

Well that didn’t work, I’ll try and figure out how to send a video

 

[smitty477]

It was going from none to pegging out rapidly. Then back to none. Less than a second time interval. I’ll try to video it if it does it again tomorrow

The vac gages have 'snubbers' on the inlets to smooth out the fuel pulses/spikes that normally occur as injectors are fired. Perhaps one of these came loose or otherwise failed allowing these pulses to reach the gage.
If you swap the filter caps/gages port to stb and the pulse follows the gage you will likely have found your problem.
Glycerin filling the gages, where possible, is another way to smooth out the pulses.

 

[O C Diver]

The vac gages have 'snubbers' on the inlets to smooth out the fuel pulses/spikes that normally occur as injectors are fired. Perhaps one of these came loose or otherwise failed allowing these pulses to reach the gage.
If you swap the filter caps/gages port to stb and the pulse follows the gage you will likely have found your problem.
Glycerin filling the gages, where possible, is another way to smooth out the pulses.

I'm having a hard time visualizing those pulses going backwards through the 2 valves (acting as check valves) in the lift pump. Also, there's always an air space in the top of the Racor that would absorb most of a backwards pulse.

Ted

 

[smitty477]

I'm having a hard time visualizing those pulses going backwards through the 2 valves (acting as check valves) in the lift pump. Also, there's always an air space in the top of the Racor that would absorb most of a backwards pulse.

Ted

I have run vac gages (not racor) without snubbers and have seen this affect at low idle rpm.
Added snubbers and it was not present after that.
Whether or not the OP's description is about this affect is less clear - but it remains a possibility.

 

[jungpeter]

Hi William983

I can't tell from your fuzzy picture-is there fluid in the gauge? It should be full, almost to the top of the gauge, with a clear liquid that assists with the damping. If the fluid's gone, suspect the gauge is gone too.

Pete