Vacuum reading opinion

[Tinker]

Originally Posted by flatjack9

Isn't there an adjustment screw on the throttle linkage? Also, what is the initial advance?

Yep, That is how you can increase vacuum. 19-21.

Fluttering could just be sticky valves. I know this is old hat, but try some mmo down the carb till it smokes, then run the crap out of it. Might just steady more from running.

Older engines had lead in the gas to lube valves. Not really needed now days to run. But the idea was lubrication, valve guides are inverted on L-blocks and see very little oil.

Try a mmo, run it, see if it helps.

Turn in or "mess" with the carb screws till vacuum goes up to around 19. I run a vacuum gauge on my 36 full time, just for fun.


Look at ignition if the motor won't accelerate well or over heats.

[Merc Cruzer]

Originally Posted by Merc Cruzer

How much would high altitude effect the overall reading?

I notice that most of the responses with the reading of around 20 are form lower altitudes (FL, NY, MI). Let me answer my own question: "How much would high altitude effect the overall reading?" . If am interpreting the chart correctly, it would be about 25% less, for a reading of around 15 at 8,000 ft. FYI: I am at 8300 ft.

https://anver.com/vacuum-lifters/atmospheric-pressure/

[JSeery]

From one source: "For example, an engine idling at 22 Hg at sea level will show approximately 17 Hg at 5,000 feet of altitude. At 10,000 feet altitude, the mercury will read about 12 Hg."

[3twinridges]

I played with carb adjustment a little yesterday and have the vacuum up to about 19 and it’s pretty steady but still has a little vibration in the needle. Thanks for the opinions. As the builder of the engine I guess I just continue to question my assembly work. I am running the 1CM cam with rotators (all new) and set the intake to 014 and exhaust to 018. I also didn’t lap the valves as the machinist and most posts I researched said that was unnecessary on newly grinded seats. Engine runs like a top and starts on the first pop but I will keep an eye on it! My vacuum gauge is a harbor freight special so that may be contributing factor also.

JB

[Merc Cruzer]

Checked mine yesterday on the 53' Merc. I rebuilt the engine around 10,000 miles ago and it reads a rock steady 14. It is 60 over and remember I am at 8300 ft. I have never had a concern, but just wanted to know. I runs up the 3,000 feet, coming back from Denver, with absolutely no issues what so ever. It has a 1CM cam.