Author Topic: 1956 Cadillac 365 engine and carb questions  (Read 3322 times)

Offline carguyblack

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1956 Cadillac 365 engine and carb questions
« on: August 24, 2009, 06:11:57 PM »
Could someone tell me what the normal vacuum reading should be with this engine at idle? I have a carb issue with my Rochester where the idle up air screw makes no difference in RPM when I turn it. After the high idle choke is off,  the engine idles extremely slow and I want to turn it up a bit. Can't effect a change and my carb guy thinks it is a engine vacuum problem. Anybody else ever have this problem? Thanks, Chuck Dykstra
Chuck Dykstra

Offline Walter Youshock

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #1 on: August 24, 2009, 06:17:42 PM »
Normal should be 18-20 HG at 420-450 RPM at sea level with transmission in DR 4 at hot idle.

HG decreases as altitude increases.

Timing also plays a factor.  Normal factory timing for a 4bbl 1956 is 5 degrees Advanced--"A" mark on the Harmonic Balancer.
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Offline John Washburn CLC 1067

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #2 on: August 24, 2009, 07:49:49 PM »
Not exactly sure which screw you are talking about (there are two for air adjusmets and one for idle)? But it sure sounds like a vaccum leak. But remembe 90% of these fuel issues end up being electrical.

Give us some more info...
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Offline carguyblack

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #3 on: August 24, 2009, 08:48:14 PM »
The adjustment screw I'm talking about is on the throttle linkage side of the carb behind the idle up cam for the choke. This is supposed to increase the RPM and then you fine tune the 2 adjustment screws at the base plate of the carb in the front. However, my idle screw makes no difference when I turn it in our out as far as RPM goes. I just hear it gulping more air as I turn it out but it doesn't increase speed at all. I can't find a vacuum leak anywhere, the wipers work fine as does the power assist on the brakes. I think that's it as far as vacuum. There is a large vacuum canister which stores vacuum for the brakes and that seems to be fine as well.
What could possibly be electrical in this mix? I have an igniter igntion (point-less) and that seems to be operating fine. Basically, the car runs well but the idle is so slow it kills.
« Last Edit: August 24, 2009, 08:50:13 PM by carguyblack »
Chuck Dykstra

Offline Roger Zimmermann

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #4 on: August 25, 2009, 09:12:07 AM »
To turn the air screw is one thing, but it's not enough. You have to play also with the 2 other screws for good idle and proper RPMs.
Roger
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Offline John Washburn CLC 1067

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #5 on: August 25, 2009, 12:31:36 PM »
Generally you want to turn the idle mixture screws in till the moter drops rpm, then turn them out (one at a time) till you get the highest rpm. You may have to do this a couple of times, but it will be well worth it.

Good Luck.
John Washburn
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Offline Otto Skorzeny

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #6 on: August 25, 2009, 01:07:39 PM »
Turn them in to seat gently by hand or you'll bung up the needles and seats.
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Offline carguyblack

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #7 on: August 25, 2009, 06:49:38 PM »
I have jumped back and forth between the 2 front screws and the side idle screw and there is absolutley no increase in RPM happening. I turn them in to "failure" and then back them out 1/2 a turn and move to the other. The engine just chugs along nice and steady but at about 100 RPM it seems. Sounds like one of those antique single cylinder tractors you occasionally hear fired up at a fair. Just can't get it to raise idle speed no matter what I tried. Thanks for being patient with me! Chuck
Chuck Dykstra

Offline John Washburn CLC 1067

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #8 on: August 25, 2009, 07:13:28 PM »
If the idle jets due not make a difference, it is time to rebuiild the carburetor. I would guess you have a vacuum leak. The idea that the windsheild wipers work fine has nothing to do with the vacuum at the carburetor.

Good Luck
John Washburn
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Offline carguyblack

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #9 on: August 26, 2009, 04:43:33 AM »
John or anyone else,
Could you tell me how I would begin to first of all, test the vacuum, and then chase the vacuum leak itself? My reasoning for mentioning the wipers was that I only see 2 spots where vacuum is conveyed and both are fitted into the intake manifold. One leads to the wiper cluster and vacuum advance on the distributor and the other is a fitting that goes directly to the power brake and storage cannister. I must be missing something so could you guys tell me what? I really am confident that the carb is fine and something else is the culprit but I am open to anything. I have tough skin so let me have it!
Chuck
Chuck Dykstra

Offline Walter Youshock

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #10 on: August 26, 2009, 07:25:17 AM »
First of all, you should have the following tools:

1. Vacuum gauge
2.  Dwell Tach
3. Timing Light

First, you need to get the TIMING as close to correct as possible.  It should be 5 degrees advanced to start.  Your DWELL on the points should be 30 degrees. 
RPM should be 420 or 450--not positive on a '56.
Hook the Vacuum Gauge to the solid line coming off the intake manifold to the wipers.

Do you have the Shop Manual for this car?
« Last Edit: August 26, 2009, 07:29:50 AM by Walter Youshock »
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Offline walt chomosh #23510

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #11 on: August 26, 2009, 08:13:17 AM »
carguy,
  The rochester carb idle speed(1955) is adjusted without touching the mechinical linkage stop.....there is a "idle air bypass"screw  on the throttle body that regulates idle speed.(located on the driver's side of the carb in the throttle body) I suspect that your throttle body gasket is leaking. After replacement on my 55CDV,my vacumn jumped to 22" unloaded,and 19 7/8" loaded(in gear).....walt...tulsa,ok 

Offline John Washburn CLC 1067

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #12 on: August 26, 2009, 08:46:08 PM »
Here is what I would suggest:

The question I hear often is how do I set the timing on my LaSalle or Cadillac for the altitude in Colorado?

One answer is to advance the timing of the distributor so that it just begins to ping under hard acceleration, then back it off until the ping stops. Works, to a degree, but takes a few tries.

My answer for adjusting timing for our high altitude in Colorado, for the gas we use here, and specifically for your engine (whether it is newly rebuilt or has lots of miles on it), is use a vacuum gauge. You canít go wrong with this method.

How does one go about adjusting the timing using a vacuum gauge? First you need a few tools 1) a good vacuum gauge 2) a good wrench to loosen the distributor nut and 3) something to plug the vacuum advance line which comes from the carburetor to the vacuum advance on the distributor.

Note: It is fairly easy to loosen the nut that holds the distributor in place on flat head engines using regular tools. But when Cadillac went to the overhead engine the distributor was still at the rear of the engines (1949 to 1962). This configuration makes it difficult to get a wrench on the distributor hold down nut. An aftermarket tool is available that makes loosening this ĹĒ nut much easier. Iíve attached a picture of two of these tools. The vacuum advance was first introduced on LaSalle and Cadillac in 1940, so prior to 1940 you donít need to worry about it. If the advance line is rubber plugging it is easy. A golf tee or a loose screw should plug the line. If the vacuum line is metal then use tape or a rubber cap to plug the line.

Now the first thing to do is find a good source of vacuum on the intake manifold where the vacuum gauge can be connected. Make sure that if you pull off a line to accomplish this task, you plug it, just to ensure that there are no vacuum leaks. Most flat head engines have a good source of vacuum in the intake manifold that connects to the double action fuel pump. To adjust the timing correctly you must disconnect the vacuum line to the double action fuel pump anyway, or you will get a false reading. Just remember to plug the line to the fuel pump.

The second task is to loosen the nut on the distributor before the engine gets hot. Trust me it is easier loosening this nut on a cold engine. Just loosen it enough so that the distributor will turn, but still with resistance. You donít want it to move easily or it will cause you problems.

The third task is to start the engine and let it  run until it reaches operating temperature.

The fourth task is to adjust the idle so it runs smoothly and you get a constant vacuum reading. Then disconnect the vacuum line to the vacuum advance on the distributor. Remember to plug the vacuum line.

Hold on, the exciting part is coming.

The fifth task is to advance the timing by turning the distributor. If the idle increases (i.e. the engine speeds up) you are going in the right direction. Now watch the vacuum gauge and adjust the distributor to obtain the highest vacuum reading on the gauge. A Cadillac or LaSalle engine in good shape will draw 18 to 22 inches of vacuum at sea level. Vacuum decreases by approximately one inch per 1,000 feet of altitude (see attached chart). So at 6,500 feet, where I live you would expect the vacuum to be in range between 13 to 17 inches. The other variation is in atmospheric conditions; any change will cause a change in the readings on the chart, just as a barometer will rise and fall with weather conditions. This is why we are looking for the highest reading of the gauge, not a listed set limit.  So what we want to do is find the distributor setting that will draw the highest vacuum, within limits. (Note: if your engine idles below the vacuum limits listed on the chart it could indicate late ignition timing, if it is higher it could indicate early ignition timing). Now once you have determined the highest setting of vacuum, drop it back into the range you think it should run. Living in Elizabeth, I would try to get it close to 17 inches of vacuum. Setting the vacuum correctly should be enough to prevent pinging, but if your car pings on the first try, not to worry (oh at this point a test drive will be in order, so just disconnect the gauge and plug the line). The gas we use makes this setting a variable. So if you do get pinging at hard acceleration, drop the vacuum back about a half inch. If that fails to get rid of the pinging try one half inch increments till you stop the pinging (make sure the gas is fairly new or  your car will run worse once you put new gas in the car). Once you get it correctly timed, verify the timing using a timing light. Write it down for future reference, with the octane of the gas, and the altitude. You now have a reference point for your car to verify that the timing has not changed.

The sixth task is to tighten the distributor down without moving it. You might want to turn the engine off to do this task. After it is tightened down start the engine and check the vacuum reading to make sure it did not change.

The seventh task is optional but strongly recommended. Adjust the idle adjusting screws (there are two of these for both two and 4 barrel carburetors). What you want to do is adjust one screw at a time. The goal is to improve the vacuum reading, but maintain a steady reading. If the vacuum gauge needle begins to bounce you went too far. To adjust turn the screw clockwise till the vacuum starts to drop, then turn the screw counterclockwise until you get maximum vacuum or as an alternative if you have a RPM gauge adjust until you reach the maximum RPM reading or highest vacuum, but no further. You may have to play with this to get it correct. Do both screws, then do it a second time to see if you might improve the vacuum reading just a little more.

If the vacuum gauge needle will not stay steady and you have verified your work then you may have other engine problems. The older Motors Auto Repair Manuals have an excellent section on determining problems via the vacuum gauge, as do others.

Finally, check the idle. Verify that it is set to specifications or as close as you can get it. Connect the vacuum line back into the vacuum advance. Disconnect the vacuum gauge and connect up any hoses or lines that go to the vacuum fitting you used.

John Washburn
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Offline carguyblack

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #13 on: August 26, 2009, 09:11:01 PM »
Thank you all for the detailed "how to" of all this! I'll be getting to this perhaps tomorrow evening with a real mechanic with proper tools and guages and I will report back my findings. After speaking with the fellow who restored my carb, I need to check the base gasket because, being human, he may have sent the wrong one which could explain my lack of vacuum. Lots to check! Now for the exciting part!....
Best to all of you,
Chuck
Chuck Dykstra

Offline Christopher Petti

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #14 on: August 27, 2009, 02:17:41 PM »
I wonder if I have the same problem with my 56,
  I have a Carter instead of a Rochester but I can hear a vacuum sound when the car is running and it goes away once I get the car into second gear. The car will also die while I'm driving at around 30-35 mph. It's never consistant. somtiems it will die on me when I'm going 5 mph. I am starting to wonder what it could be. I never checked the vacuum. I should probably retime the car. that might be a good idea. I just put on a new exhaust and replaced all the vacum hoses. Hmmmm. I'm putting a new stainless fuel line on and checking the gas tank for crud this week. I did see dirt in my carb last time I took it apart last week.
And uses too much gas
Some folks say it's too old
And that it goes too fast
But my love is bigger than a Honda
It's bigger than a Subaru
Hey man there's only one thing
And one car that will do
Anyway we don't have to drive it
Honey we can park it out in back
And have a party in your pink Cadillac

Offline Walter Youshock

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #15 on: August 27, 2009, 05:52:25 PM »
The other thing to check is the bakelite plate that goes under the carb.  They can develop small cracks from age and heat.
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Offline John Washburn CLC 1067

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #16 on: August 27, 2009, 07:11:21 PM »
Walter,

No heat sink, bakelit, was used on the 56.

The Carter carb, due to folks modifying them would stall when one made a left turn. If this is the case I can provide the fix, per Cadillac Serviceman.
John Washburn
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1956 Coupe DeVille

Offline carguyblack

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #17 on: August 27, 2009, 07:33:25 PM »
Here's the update after extensive analysis by an expert with some very expensive test equipment. Timing was set, ignition was checked and cylinder firing, valve seating and compression was all checked and indicative of a brand new engine. Vacuum, however, was at 14-15 at 430 RPM and we couldn't get the RPM to change no matter what we adjusted on the carb. It was ultimately left at an adjustment mix where the engine ran smooth and steady with the optimum vacuum between all 3 set screws. The mechanic's opinion was that the engine was so new and only been run about 50 miles that there was so much cross hatching on the cylinders that it hadn't broken in yet. He thought the vacuum would steadily increase as the engine got worked in. It ran very well at idle. We did find one issue which was under load (flooring the accelerator) it would not take the fuel and would backfire and shudder and blow smoke out  the rear. We found that the coil was only putting out very little and was defective. I will be replacing the coil as soon as I locate one that is matched to my igniter. I didn't mention that we switched out carbs during our work tonight, too. We wanted to rule out a defective carb issue. I have 2 rebuilt and restored Rochesters so we changed them over to see if the gasket was leaking or if one of the carbs was faulty. They both operated identically and both ran beautifully. The vacuum remained steady at 15 at 430 RPM. This is our conclusion and I will need to run the engine quite some time now to see if his prediction is correct. As it is, the car runs great and the very low idle I thought I was having is actually at the set point it should be at. I'm just used to modern cars having an idle around 800. As long as it doesn't kill, which it isn't, I'm going to be satisfied. Hopefully, the vacuum will rise to about 18-20 when the engine is fully broken in and seated well. The fact that I can't raise the idle at all still puzzles me, but I'm hoping that is a function of the vacuum rise as the engine gets broken in.
Anything wrong with this logic? Thanks for reading my "essay" and for your advice.
Chuck
Chuck Dykstra

Offline kelly

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #18 on: August 27, 2009, 09:05:21 PM »
Chuck,
  What you hear is the sound of me scratching my head. I am looking forward to hearing how this works out. You know, I remember an oldtime master mechanic telling me to go old-school on vintage engine break-in. He suggested non-detergent motor oil for faster break-in.  Anyone else out there heard that before?
Kelly Martin
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Offline Otto Skorzeny

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Re: 1956 Cadillac 365 engine and carb questions
« Reply #19 on: August 27, 2009, 09:40:11 PM »
I hear all kinds of things from take it easy, don't go over 60 for the first 500 miles to floorboard it in the garage for 30 minutes the first time it's fired up.
fward

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