1960 rough engine Timing question SOLVED

[60eldo]

 Just woke up and was doing some reading on an old post here, he had same problem. Is it possible, that a rotten choke tube could cause a vac leek? Mine is rotten and I forgot to tell the rebuilder about it so its still leeking, so I plugged it at the top. But maybe its leeking at the bottom. Is this possible.

[dn010]

Editing post: If the choke tube is connected to the intake, a rotten tube could cause a vacuum LEAK but from other posts written on this, it would be a very small leak.

[60eldo]

  Im talking about the one thats in the intake manifold. If rotten,wouldnt  the manifold be sucking in air there unless both sides upper and lower were plugged or a new tube be put in.

[Roger Zimmermann]

Editing post: If the choke tube is connected to the intake, a rotten tube could cause a vacuum LEAK but from other posts written on this, it would be a very small leak.

Rotten or not, that has no importance as the tube is open at the other end. If the tube is rotten, the carb will suck exhaust gases into the choke coil which is no good for its function.

[60eldo]

 I went with manual choke now so that wont affect me. I just wanted to no that if a choke tube were rotten, could that cause a vac leek. Im grasping at straws now.

[TJ Hopland]

I have not taken apart a 60 intake but typically the choke heater tubes don't cross into the intake side of things.  They are routed through the exhaust crossover section which does not connect with the intake till 73 with the introduction of EGR unless it was one of the designs were there was an opening under the carb that was sealed by a special base gasket or the carb itself.  Those should be pretty obvious with the carb off because there will be a extra hole other than the main ones you see aligning with the throttle bores and connecting to the main runners. Those require a special gasket to deal with the heat.  If a gasket was used from a different year or model that didn't have that opening it would burn up fairly quickly and basically be an uncontrollable EGR system.

So the choke heater tube is in the intake as in the intake manifold as an assembly but its not in the section that carries the air from the carb to the intake ports on the heads.  If both ends of the damaged choke tube are not plugged its just going to leak a little exhaust an the only damage will likely be from the heat and corrosive nature of the exhaust.  It really should not have any effect on how the engine runs till if and when it damages something else.

[dadscad]

Basically, there are 3 areas that have the most likely potential for a vacuum leak. 1. Intake manifold to head gaskets. 2. Carburetor to intake manifold gaskets. 3. Attached vacuum accessories. The integrity of those 3 areas need to be verified. The next two are less likely but they do appear occasionally. A 4th possibility, is a damaged carburetor body or carbureator base plate which would not seal on the gasket. Look for cracks or a warp in the base of the carburetor. A 5th possibility would be a cracked intake manifold.

[60eldo]

Well iv tryed everything over and over again in a 3 week period, and i cant get more than 15-16 on vac, car still stumbles at stop. Moving the dist either way does nothing, when i set proper timing with gun , vac goes down to 10. Screws on carb do very little. Wed, I have an appointment with a good shop here, hope they will find it. Maybe its a sticky vale, maybe its this, maybe maybe. IM DONE

[Lexi]

I have not taken apart a 60 intake but typically the choke heater tubes don't cross into the intake side of things.  They are routed through the exhaust crossover section which does not connect with the intake till 73 with the introduction of EGR unless it was one of the designs were there was an opening under the carb that was sealed by a special base gasket or the carb itself.  Those should be pretty obvious with the carb off because there will be a extra hole other than the main ones you see aligning with the throttle bores and connecting to the main runners. Those require a special gasket to deal with the heat.  If a gasket was used from a different year or model that didn't have that opening it would burn up fairly quickly and basically be an uncontrollable EGR system.

So the choke heater tube is in the intake as in the intake manifold as an assembly but its not in the section that carries the air from the carb to the intake ports on the heads.  If both ends of the damaged choke tube are not plugged its just going to leak a little exhaust an the only damage will likely be from the heat and corrosive nature of the exhaust.  It really should not have any effect on how the engine runs till if and when it damages something else.

I agree with TJ. In that era it is just a tube that by way of convection carries heated air to the bi-metallic spring in the choke housing. Its decay should not be a factor in your case. On my car this tube runs from a sealed chamber on the exhaust manifold, but it does not even carry exhaust gases. The exhaust runs underneath this "hot box" which is a separate cast area which gets heated from the exhaust gases below. A little like a pot on a hot stove. The element heats the contents of the pot but the two are not connected, (at least in my case). Clay/Lexi

[dn010]

The choke tube is designed to carry heated air to the spring, the manual states for both 4GC and AFB that vacuum is applied to the choke housing via the choke piston in order to bring the hot air up and past the coil spring to heat it up. So there is vacuum in there, but it should not be enough to cause problems should the tube be rotten. I wouldn't worry about this as a cause of the engine problems described and would look elsewhere.

[Big Fins]

There are more issues with this engine other than vacuum. A 390 is a stand alone perfectly running engine when it's built right and tuned. Just like any Cadillac engine from the 425 on back.

I don't know the person, the set up, or the degree of knowledge of the car, so hard to be able to diagnose this over the Internet.

Best of luck getting it corrected.

[60eldo]

  Took the car in today to see if they could find my vacumn problem and Im at a bit of a loss. He rebuilt my dist. and put in electronic ign. He will put dist. back in tomorrow. Im wondering why he started there. Hows rebuilding the dist. gonna give me more vac?

[TJ Hopland]

The vacuum reading is related to having a happy engine.  Timing and mixture effect the vacuum reading.   If the timing advance wasn't working right or sticking that would not be helping things.  If the bushing was worn the shaft which has the points cam on it could be wobbling around randomly changing the dwell and timing which won't help things.  Going electronic may be more tolerant of a worn bushing but hopefully they replaced that bushing as part of the rebuild if it needed it. 

[James Landi]

"The vacuum reading is related to having a happy engine.  Timing and mixture effect the vacuum reading.   If the timing advance wasn't working right or sticking that would not be helping things.  If the bushing was worn the shaft which has the points cam on it could be wobbling around randomly changing the dwell and timing which won't help things.  Going electronic may be more tolerant of a worn bushing but hopefully they replaced that bushing as part of the rebuild if it needed it."

Had that happen, and it can drive a sane person NUTS!!.  The plate where the points are mounted is pressed on to a stationary hollow shaft  (with no lubrication at the bushing) on the distributor.  Over time, the vacuum advance had pushed and pulled that mounting plate so many thousands of times, that the plate had developed an oval at the center, thus, after setting the dwell up...(accomplished at idle speed), any acceleration of rpm that would trigger the vacuum advance to move, caused the dwell to radically change.  Since this occurred on a marine engine, I could hear an odd popping out of the exhaust at speed... then, I'd go back to set the dwell, and, of course, it was way off once I tested the engine. I finally used a slotted screw driver : pushing the point's mounting plate against the distributor shell-- mystery solved... the "play" was obvious-- the mounting plate was very worn. 

[60eldo]

 So we found the plugs being very light color, so its running very lean. I called the guy who rebuilt the carter 3352S carb and he told me to take it off and he will put in bigger jets. Does anyone here no the number for correct jets,,,,thanks

[TJ Hopland]

'Correct' jets is going to depend on the rest of the build and can be difficult to calculate so the only option may be to just guess and go a size or two bigger and see what happens.   I assume the shop can't find any vacuum leaks and the distributor work didn't really change anything?

[cadman59]

The jets do nothing at idle, so I'm afraid that won't correct your idle issues.

[PHIL WHYTE CLC 14192]

So we found the plugs being very light color, so its running very lean. I called the guy who rebuilt the carter 3352S carb and he told me to take it off and he will put in bigger jets. Does anyone here no the number for correct jets,,,,thanks

It could run lean because of a vacuum leak or an air leak ( cracked intake manifold for instance), or just the timing being out.

[60eldo]

Taking the carb back to the rebuilder, the plugs are running white, very lean. Hes gonna change the jets, bigger, and the mechanic said I need new step up springs. Also now have  a hard brake pedal, must be booster. When it rains it pours. I wish I had another carb so I could through on just to see if thats my problem.

[James Landi]

Jon,

Your old, worn out engine did not stress other old, "end of service life" parts.  I suspect the massive leak in the brake booster was the final straw regarding your lack of vacuum.  While the carburetor is returned,do urge the rebuilder to check to ensure that the throttle plate is entirely closed and that there are no possible vacuum leaks around moving parts and gaskets.  The fact that your idle adjustment screws were meaningless points you in the direction of a fault in the carburetor..... white spark plug residue certainly amplifies that mysterious vacuum leak diagnosis  James