Vacuum test

[dgmgohl]

I have a 53 Merc 255, and I'm preforming a vacuum test of the intake. I'm reading 19. I can't find the right spec on where it should be. I was told around 25. If that's the case is there a way to increase the vacuum to normal specs?

[BUBBAS IGNITION]

Let google be your friend .........

[Talkwrench]

Normal vacuum on a good engine at sea level will be 21Hg. the "norm" is between 17 - 21Hg.

[19Fordy]

Actually 19 isn't bad, I think.

[Ggmac]

If it's a steady needle, that's not bad .

[tubman]

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This is assuming a stock engine. Aftermarket camshafts can cause lower vacuum readings.

[37 Cab]

As can timing adjustments. Slow timing= lower vacuum

[Ol' Ron]

19 is very good especially if the needle is steady. You might want to 'Tweek" the idle screws on the carb, for more, but?

[scicala]

I would be more than happy with 19" with a stock camshaft.


Sal

[Flathead Fever]

Its good at 19 especially if your at a higher elevation. Another test is to snap the throttle open and closed and see if the reading momentarily goes up even further, then drops back-down to 19. That tells you your rings are seating well.

[Tinker]

19" is solid. 24-25" would be too much at idle in my opinion no matter the elevation (that's if you take the measurement at that elevation).


As mentioned google is your friend. many articles on it.

Oldie but a goodie.