Are there factory spec vacuum levels?

Stevehose

Stevehose

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Having just rebuilt and tuned my carbs (partly by using vacuum gauges) I am curious to know if there is a factory spec amount of vacuum that should be seen at the manifold (non-ported) for a stock 3 liter carbed? I am getting about 14 HG at idle, is this within range, high, or low? Also, is there a number or range for the ported vacuum amount, say at 3000rpm or so. What say the forum experts?
 
IMHO - 14 is a tad low... 17 to 19 " is good to see. I would be looking for reasons if I saw 14.

Check that timing for retard- retard will drop vacuum.
Check those diaphrams in the vacuum box at the distributor for torn condition
Check for lean condition- lean will bring down vacuum readings.
 
Don thanks for your suggestions but:

-My timing is a tad advanced, seems the pertronix likes it that way.
-Since the distr is hooked up to only one carb I would think that since both my carbs have same Hg then that isnt a problem, also it manually holds vacuum until released.
-I tuned my mixtures in part with a vacuum gauge on each carb - if anything they are a 1/8 turn on the rich side per other reccomendations here on the forum for best running.

I am below sea level here so I should have high vacuum!

I am going to check valve specs this weekend, could that cause vacuum issues?

Anyone care to take a manifold reading for each carb and report, or can find an official E9 spec for vacuum?



sfdon said:
IMHO - 14 is a tad low... 17 to 19 " is good to see. I would be looking for reasons if I saw 14.

Check that timing for retard- retard will drop vacuum.
Check those diaphrams in the vacuum box at the distributor for torn condition
Check for lean condition- lean will bring down vacuum readings.
Click to expand...
 
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Engine Vacumn

Steve,

My vacumn at the manifold and not the carbs is 18 in and my engine is running fine but not fresh. There are guages that read several different measurements of vacumn. In checking my timing, I hook up the vacumn guage and the timing light. First using the guage to get the highest reading by rotating the distributer, then backing off a 1/2 in of vacumn. Then check the timing and you should be close. Since every engine is different and some are worn differently than others, there will be differences.

You asked a question about what was standard; besides the general rule that Don talks about, the factory specs on the distributer advance on the ported vacumn are a check. ( RPM, vac, degrees) But you would have to have an advanceable timing light, tach, and guage rigged up and use TDC.

I would also suggest that static timing with a Pertronix be double checked and that it's down all the way on the shaft. Mark on the damper, rotor on the notch, and maybe even see if you can get a read off the reluctor magnet ( wheel)- the same as a set of points with a meter. Yes, they do tend to be advanced in position. That's where the guage reading is the double check against the timing mark. And I'd check my all in advance ( mechanical and vac.) at speed. I'm sure I'm not the only one who fooled himself with looking at the wrong timing ball- I painted one red!

The only other thing is the retard. It was emissions, controlled by a temp sw and a solenoid. I don't have it and maybe others can report as to what to do with it as probably most of those devices gave up the ghost long ago.
 
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So to be clear you do this adjustment technique at idle, then up it to 1700rpm and check per the manual?

61porsche said:
In checking my timing, I hook up the vacumn guage and the timing light. First using the guage to get the highest reading by rotating the distributer, then backing off a 1/2 in of vacumn.
Click to expand...
 
As Porsche 61 says - the timing can be a mess on these cars. Long ago I adopted a practice of setting all the cars that I work on to TDC at the dampner and then turning the flywheel 7 teeth by hand. I apply a dab of paint at the 7th tooth which coincides with a ball or a mark or a line or whatever. [360 degrees / 116 teeth = 3.1 degree per tooth ]
I keep a record of all the cars that were set 22 degrees retarded and the cars that were put back together w/o the positioning dowel on the flywheel. Not pretty...
Things to keep in mind - BMW used a host of different types of marks on their flywheels including some flywheels with THREE marks ie TDC, IDLE, and 2200 rpm. Unless of course it was California version and the timing is set at 3500 rpm on some cars...

Check your crank timing and famiarize yourself with the flywheel marks on your car.
 
So if I manually set the engine to TDC with the pulley/distr rotor method, will there be a mark/pressed ball visible in the timing window also? And is this mark/ball different than the one used to set timing per the book? I'd like to paint the correct one so it's not mistaken when strobe-ing. Thanks for this info - much appreciated.

sfdon said:
Things to keep in mind - BMW used a host of different types of marks on their flywheels including some flywheels with THREE marks ie TDC, IDLE, and 2200 rpm. Unless of course it was California version and the timing is set at 3500 rpm on some cars...

Check your crank timing and famiarize yourself with the flywheel marks on your car.
Click to expand...
 
Timing

Yes, there are two timing balls.

Yes, if you line up TDC on the balancer; there should be a second ball in the timing window. But there is a third check- the rotor position and a mark on the edge of the distributer.

I'd trust the damper over the other two. That's why they sell degreed dampers, tabs, and timing tapes.:)
 
BTW- many times you will see a T/O and a line or you can see a Z and a line... and yes there are the little balls or bb's.
Set the TDC at the front and check for the mark at the bellhousing opening.
Use a big screw driver on the teeth to move the flywheel 7 teeth. Now you will see the timing mark- Paint the bastard!
 
This could be a stupid question but when discussing before and after TDC I want to make sure, should I move flywheel clockwise or counter clockwise when looking at it through the window?

sfdon said:
BTW- many times you will see a T/O and a line or you can see a Z and a line... and yes there are the little balls or bb's.
Set the TDC at the front and check for the mark at the bellhousing opening.
Use a big screw driver on the teeth to move the flywheel 7 teeth. Now you will see the timing mark- Paint the bastard!
Click to expand...
 
Timing

Best clockwise.

The reason being that's the normal rotation. With chains, sprockets, wear, etc. rotating counter will most times add some slack. Sometimes as much as 7 degrees or more from what the reference is.

Make a chaulk mark on the damper about an 1,1/2" BTDC on the damper , slowly rotate and find the first timing ball. Clean it off well, Then slowly continue to turn until you see the second or TDC ball. paint that one a different color. Some guys paint white between them. Or count teeth as Don suggests.
 
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