'39 LZ Vacumn Test Results/Next Step Compression Test

Since it is easier to run a vacuum test than a compression test I started with that.

I disconnected the line that goes from the intake manifold to the windshield wipers.

I installed the vacuum pressure gauge and let the engine warm up for about 15 minutes to make sure it go up to operating temperature..

The readings are as follows:

At a steady idle the reading was about 18.90 inches and held fairly steady. When I quickly increased the throttle speed it bounced from about 1-2 inches to over 20" and then settled back to 18.90"

I turn offed the engine for about 10 minutes then started the engine again. This time I got reading of 19.05" plus or minus. With the throttle increase test it bounced form 2-21 and then returned to 19.05.

I have never done a vacuum test in my life so I hoped I followed the correct procedure.

According to qauge the vacuum is within the normal range. My understanding that between 17-21" is considered normal.Can anyone confirm that my readings are within normal for a 'LZ V12.

Note: it takes quite a while to get my engine up to operating temperature. Prior to reaching operating temperature the engine idles roughly and occasionally gives me vacuum reading that will fluctuate between .05 and 1.00".

Your vacuum readings sound normal. The thermostats or lack of may be the cause of the slow warm up? These engines normally warm up very quick. The thermostats are located inside the upper hoses. Several things can cause rough idling but I would check the carburetor. The old power valve had a habit of leaking ( with modern fuel) causing a rough/rich idle. A sure indication would be if adjusting the mixture screws has no effect on the idle quality.

Peecher,

Thanks for the advice. Its nice to know the vacuum reading are "normal"

I will check on the thermostat.

In terms of the caburetor I bought the one I am using from George Trickett about three years ago. I recently noticed that one of the two needle valves used for fuel/air mixing each of tho barrels had its head sheared off so it is stuck in its present position.

The other needle valve only seems to have an affect on the idling when it is turned to the extreme left or right. In other words once you back off the needle valve from the extreme right about 2 turns the idle seems to stabilize but will not allow any further adjustment.

My spark plugs are getting a carbon build up (not wet or oily) and which I think is due to a too rich a mixture.

I am going to try to extract the broken needle valve (any advise on how to extract the needle valve would be helpful for me) and install a new one so I can properly adjust both barrels of the carb.

Since the carburetor was supposedly rebuilt by George Trickett I wonder if the power valve was replaced. I am really not familiar with the inner workings of carburetors so I will have to study a manual to find out more about what the power valve does.

I will let you know what I find. I might also consider buying a new Holly 97 that is being reproduced and sold by vintage Ford parts dealers. Any thoughts on going that route.

Keep the advice coming it really helps.

Best regards,

Sorry I meant to say Stromberg 97 not Holly.

Your Holley Carb ( fixed properly) is actually superior to the Stromberg 97. Unfotunately the throttle arm on the 97's (unless a '38 Lincoln Zephyr)operates in the wrong direction for the Lincoln linkage. Not sure if the aftermarket "new" 97's can be converted to the push-to-open mode?

Removing the broken needle can be tricky. I have had luck by carefully drilling a small in the center about 1/4" deep, and small enough that I can tap/drive in a short piece of square tool stock. Then carefully, using a small cresent wrench unscrew the broken needle with the aid of some good penetrating oil.

When the carb is in good shape you should be able to get a smooth idle with the mixture needle(s) about a 1/2 to 3/4 of a turn out from seated. George T is pretty thorough but you might check the bottom of the carburetor bowl for warpage which will effect the vacuum seal. This condition is often overlooked and if there's enough vacuum leakage between the bowl and the throttle base the power valve will remain open causing a rich mixture. Good luck.

Peecher,

Yesterday I ran a vacuum test on the engine and it held steady at about 19". Will the vacuum test indicate whether there is a leakage between the bowl and the throttle base or there some other test I can perform aside from a visual check of the bottom of the carb.

The steady 19" hg would sure indicate the engine is in good shape. slight vacuum leaks at the power valve chamber would'nt affect it that much. If it's not running rich then maybe you're ok? The broken off mixture screw and questionable power valve operation should be attended to however.