Setting timing with vacuum gauge - 49 Olds Motor

[57j2olds]

Ok so I guess this is a dumb question, however where do I hook up my vacuum gauge on my 49 Olds motor straight 6?

 

Do I disconnect the distributer vac line and hook it up there?

 

Thanks

Edited August 19, 2023 by 57j2olds (see edit history)

[Grimy]

Windshield wiper line

[57j2olds]

So I found a small 8th inch pipe plug in the intake manifold. I’m assuming that would be my best bet.

 

The wipers are not hooked up. 

[Grimy]

If the wiper's vacuum *port* is available (i.e., not squeezed shut by pliers), that would be easiest and you don't risk wringing off the pipe plug that probably hasn't had a wrench on it since the car was new.  And the accuracy of the pipe plug depends on location--does it provide access to all cylinders?

[57j2olds]

Yes it does. 
 

this is the first time I’ve ever hooked up a manifold vacuum gauge to this car. When I just started it, I was about 18 inches of vacuum. Advanced the distributor slightly and I got it up to 20 and it’s holding at 20 now.

 

Does that sound about right?

[TerryB]

Twenty sounds good. If your gage is color coded, that should be high up on the green scale of the gauge.

[Grimy]

The old "power-tuning" technique of my long-ago youth:  Warmed up engine, at slow idle: advance to maximum vacuum reading, then retard by half-inch of mercury (i.e., if max is 20.0, retard to 19.5).  test drive.  If you get pinging on hills, retard another 0.5 inch.

 

Another fun test with a vacuum gauge to see if you have exhaust system clogs (critter nests or carbon buildup in muffler):  Warmed-up engine at idle, gauge hooked up.  Have an assistant rev the engine to about 1,500 rpm and hold rpm steady for TWO FULL MINUTES while you monitor the vacuum gauge.  It will take about 15 seconds for the gauge to stabilize when the rpm is first increased.  When the gauge stabilizes, make a note (mental or written) of that value.  Then note the reading at the end of two minutes.  If you get a continually reducing reading over the two minutes, that's an indication of a clogged exhaust system, and you should check it out further.

[Bloo]

I would expect a 49 olds to have a vacuum pump for the wipers. Be sure you are connected directly to the manifold and not to the pump.

 

[rocketraider]

Vacuum gage is a useful yet often overlooked tuning tool. Steady 20"Hg tells me the 257 is in very good condition.

 

Once you get timing sorted out, the vacuum gage can also be used to set idle mixture. Adjust the idle mixture screw(s) to achieve highest vacuum reading at normal idle speed and wa-la! Your Big Six should purr like a kitten that was just fed!

[57j2olds]

Thanks guys!

 

Funny, you should say that I just got done with the idle mixture.

 

The car is all original. It’s been sitting in a barn for 45 years. Original 35,000 miles.

 

If you can tell me a little bit more on that 257 motor, it would be great. I love the history or I’d love to know the history behind it.

 

Got it from the original owner   He vaguely remembers the original 48 motor throwing a rod back in the early 50s. I guess it’s better that they put a 49 motor in it.

 

A Very kind member of this forum currently has my NOS distributor. Even though it was new old stock, the grease in it was hardened and had leaked all over of the points due to it laying on its side for 80 years.

 

I should have the new distributor next week.

 

 

 

[dodge28]

Below the butterfly. (Throttle vacuum)