520H Vacuum Gauge readings

[BaySide1 138]

New to the 520h. What should I be seeing for a vacuum reading on the gauge.

 

Standing Reading at idle?

What causes it to rise and or fall?

Is this engine vacuum or  a hydraulic vacuum?

 

Thanks

[gwest_ca-(File Mod) 11,039]

It is engine vacuum but the operator's manuals seem to differ in their description and appear to contradict each other unless they are calibrated opposite to each other.

#5 is 1988 and #4 is 1993-96. Hopefully an owner can tell us which is correct. 

Engine vacuum is taken from a port after the throttle plate. Higher is better.

Sometimes a vacuum gauge gets it's signal from the air cleaner ahead on the throttle plate to indicate the condition of the air filter. Lower is better.

 

Garry

 

 

[Pollack Pete 2,273]

Vacuum will be highest at idle.Vacuum will fall of as engine rpm increases.I could never understand why ,except fot tune-up reasons,anybody ever installed a vacuum gauge on an engine..Just another gauge to look at,I guess. .Good for adjusting a carburetor though.

[WVHillbilly520H 10,373]

They both are correct, #5 standard vacuum gauge when you open the throttle the vacuum drops as rpms rise then on the newer models #4 it's obviously calibrated different to show amount of hp being used ,as for me normal WOT while mowing normally reading steady at 75% +/- but heavy tall grass and deep snow blowing near 100% when the governor opens up and at idle needle fluctuates around 25% +/-, just my experiences with my 520s and tuning carbs with a standard vacuum gauge also the stand alone vacuum gauge can give you an idea on ring/valve seal/condition throughout the rpm range, Jeff.

[squonk 41,050]

For years I used a vacuum gauge to diagnose engine troubles and do tune ups. Low vac-retarded timing, rapid swing-sticky valve, drifting back and forth- lean mixture. ect. I still have a couple kicking around. I wish there was a port to install one on a K301.  

[AlexH 2]

Mines stuck between 100 and like 85 what does that mean?

[lynnmor 7,303]

3 hours ago, AlexH said:

Mines stuck between 100 and like 85 what does that mean?

 

First, make sure that you have a good hose with clamps connected to the intake manifold and the gauge.  If that doesn't fix it, then a new gauge is in order.  100% means that there is little vacuum and the engine is working as hard as it can, of course with the engine stopped it also is reading 100% because it is working as hard as it can.