1935 Cadillac V-12 Loss of Power

We are having a problem with our ’35 Cadillac V-12 losing power. Here are the symptoms:Car runs well at idle:

• Drove to gas station to fill up.
  
• Drove about 7 miles, performed flawlessly
  
• Let it sit about 20 minutes to begin detailing
  
• Started it, it idled smoothly
  
• Went to drive it, had no power (behaved like vapor lock)
  
• Electric Fuel pump did not solve problem.
  

Cracked fuel lines, got only fuel, no air. Timing is correct. Car is not overheating. Idles well.

Car has (in the past year):

• New (rebuilt) coils
  
• Rebuilt Fuel Pump
  
• Electric supplemental fuel pump
  
• One of the two Detroit Lubricator 51 carbs was rebuilt as it had a sticking needle and seat which caused it to hemorrhage gas.
  

Has anyone else experienced similar problems with the V-12 or V-16 engines? Is there an problem with the DL 51's?

While we are pretty sure it is a fuel problem, we cannot find the source. (I know, 90% of all fuel problems are ignition)

Any help greatly appreciated.

Pat

It wouldn't hurt to change the condenser, as sometimes when they fail they show symptoms like yours. You might pull a wire and check the spark at a plug as you rev up the engine -- it should be bright and bluish.

James:

We put new condensers in recently, but we are going to replace them again anyway. I have actually found new ones right out of the box that were bad! In checking the plugs, it appears that the right side plugs are burning much leaner than the left. (the V-12 has two separate ignition systems). We are going to rebuild the right carb (the left had been done last year).

Pat

I'm not familiar with your car's ignition system but if dual ignition means dual coils, you might consider that one coil is beginning to fail. I just went through this on my 34 Packard with dual coil ignition.

A good thought. Our ignition is very similar to your Packard ignition. I had both coils rebuilt (actually new coils inserted in the gutted Cadillac coils) last year. It was my original thought that the coils were overheating and thus failing.

Thanks, Pat

Pat,

I am no expert but I chased problems on a 32 V-12 for a few years. Good advice to check and recheck coils and condensers, I had a brand new set of coils go out in less than 6 months. Also check your points for both gap and synchronization in case the adjustments loosened up. As far as the Detroit Lubricator carbs, I was told by an expert that they were an obsolete design when they were brand new! The biggest problem today is their pot metal construction which can swell from age and render them inoperable. I replaced mine with Zeniths in order to make it run right. I can tell you from experience that the V-12 will start, run, and even idle pretty smooth when running on only one bank of 6 cylinders but has no power - check to see if the exhaust manifold on one bank stays cool! I wish you luck.

Hi Don:

Thanks for your input. Great idea to check exhaust manifold.

I had seen your post about your carburetors (about two years ago?) and your final shift to the Zeniths. We won't be able to change carburetors, at least not for the near future, as this car has been invited to the Pebble Beach Concours (actually, it will be the third time to go with the same 37 year-old restoration).

We have had pretty good luck with the Detroit Lubricator 51's. We have one on our '29 Packard which we have taken on quite a few long tours with no problems. Having said that, I have learned from the Carburetor Shop that the vane mechanism can wear, causing the vanes to hang up. I do agree that the pot metal sucks, but ours are in pretty good shape.

I normally do all my work, however, it is currently in a shop where they have a lot more room and a crew that are prepping the car for Pebble Beach. I am just assisting in chasing down ideas for him.

After this year, we plan to drive the car more often.

Again, thanks for your input.

Pat

Pat,

I have a 1936 Cadillac V-12 that is having the same power loss that is discussed here.  I have tried new coils, new condensers, electric fuel pump. rebuilt carburetors and points are good.  Engine will run fine for about ten minutes and then lose power.  Rest for a while and then will start fine but later lose power again.  It is the right bank that seems to just stop working.  Curious to know if you discovered what was causing your problem.  Any help would be much appreciated.

Cy Strickler
cwstrick@comcast.net

Cy, I do not have any practical experience with your predicament, however you might want to talk with Scott Henningsen in Speckles California. As you may know he currently makes an exact reproduction Detroit Lubricater Carburetor for Cadillac V-12 & V-16 along with late twenties and early thirties Packard.  He sometimes can rebuild your core, but many of those cores are starting to distort.  These new carburetor’s will never do that, plus you will reduce your chances of a fire. Last time I checked he is nearing 200 new Carburetor’s and he puts them on a test engine when done. Full disclosure, I do not receive any financial gain if you buy a carburetor, however I might get a glass of wine 🍷 if you do

I would try a H.F. spark tester light and see if you are losing spark at higher revs.  I had that problem last summer and found the spark was arcing through the roter to ground.  It will also tell you if your ignition is breaking down.

Another possibility is a bad distributor cap that breaks down after it heats up. 

I will send you a PM, as I have Delt with this issue multiple times......there can be several causes.......

Thanks for the responses.  I am aware of Scott Henningsen's carburetors but would like to avoid that financial investment if possible.  I will call Ed tonight and see what hints he might have.

Cy

You should find out what.s wrong by testing your exhaust gas when the problem is present. A 4 gas tester  will tell you what causes your power loss. Fuel or ignition related. From what you describe ignition related has my vote , new condensors are shit, but if  they will stay gone, also not comeback. As two previous responders mentioned , cap or rotor, one or both. Would be interested to know what you will find. Please let us know Johan

I've got $5 on the coils. Even though they're new, they aren't necessarily good. With the location of the coils on the Cadillac V12, they get really hot and that's when they fail. When they cool off, voila! They magically work again.

9 minutes ago, Matt Harwood said:

I've got $5 on the coils. Even though they're new, they aren't necessarily good. With the location of the coils on the Cadillac V12, they get really hot and that's when they fail. When they cool off, voila! They magically work again.

I give that one chance in 20.............certainly on the list, but way down. 

Same exact thing happened to a 1949 Dodge I had. It was the coil.

I see said the blind man picking up his hammer and saw, You do said the deaf mute?; while the man with no legs got up and walked away.............

Just now, keiser31 said:

Same exact thing happened to a 1949 Dodge I had. It was the coil.

Says he has new coils....which means absolutely nothing. Easy way is to swap them and see if the problem moves, which I bet it will not. 

I had one of those problems at one time. 

It turned out to be where the circuit for the distributor wire goes from the outside to the points inside of the distributor.  The circuit is through the distributor housing using a bolt that is surrounded by an insulator sleeve.  Turned out the sleeve was cracked and allowed the circuit to go to ground and the engine would miss or stop.

Just a thought.

Turns out that I had a double problem.  I put in new points, and in the process discovered that the right bank set of points was shorting inside the distributor because the tension spring was to close to a screw head below it.  Made adjustments and engine fired up fine.  Went for a test drive and did great for five minutes and then right bank quit.  Troubleshooting found that fuel flow was minimal even with electric fuel pump.  Checked the fuel tank and found it totally clogged up.  It appears that the engine could get enough gas to start, but once underway would reclog and stop fuel flow.  Since electrical problem on right side was intermittent, it was hard to diagnose.   On the V-12, fuel for the right bank goes up and over the engine from the fuel pump.  Apparently. the fuel flow was enough to just keep the left side running but not enough to push fuel over to the right side.  Have the tank out of the car, and now I have the new problem of making it foolproof going forward.  Anybody a fuel tank specialist?

On 2/12/2024 at 2:08 PM, edinmass said:

I will send you a PM, as I have felt with this issue multiple times......there can be several causes.......

Would you consider sharing your thoughts to the forum. Other members may be experiencing similar problems and search the forum for solutions. I for one are experiencing similar problems with a Cadillac V12. The car is on the back burner for now while I work on the interior. I hope to get back into the running issues later this spring.

The lack of power may be that you are losing one bank.   The V12 has dual exhaust, correct?   Check that there is exhaust exiting both pipes when this happens.

I swear 90% of the time this ends up being either the Coil or Condenser.

Another possible cause is clogged exhaust on one or both sides due to baffle collapse or mouse nests.  Here's how to test, running one bank (only) at a time on dual exhaust vehicles:

With a warmed up engine, add a vacuum gauge (disconnect the vacuum wiper feed).  Have an assistant run the engine at about *steady* 1,500 rpm for two full minutes while you monitor the vacuum gauge.  It will take 15-20 seconds for the gauge to stabilize as the engine is initially revved up.  Note the vacuum gauge reading when it first stabilizes.  At the end of two full minutes, again note the vacuum gauge reading.  If there has been a substantial drop during the two-minute period, particularly if the gauge continues to fall, you have some form of exhaust system blockage *on that bank.* 

This is a minimally intrusive diagnosis, meaning that you don't need to drop any exhaust components unless suggested by the results of this test.  And it's even easier on a single exhaust vehicle.

Years ago at the Franklin Trek  the New England Boys arrived with Frank Netetoms car backfiring , loos of power ect . I reached down and touched the coil .it was on fire.... I poured some cold Budweiser on it and magically the coil worked again. Off the the NAPA  he went and got a cheap universal 6 colt coil and problem was fixed.

On 3/9/2024 at 1:26 PM, mikewest said:

I poured some cold Budweiser on it

A universal tool.

I watched  one of Dale Jrs Shows and he told a story about go kart racing on his back 40.

He was sponsored by Budweiser at the time and had a bunch of it.

They used beer to add moisture to the back yard track. Lots of beer.

He showed some videos showing fun times with several famous racers in the mix.

Fuel lines that are over or near hot surfaces can easily vapor lock. If you have a line running over the engine, make sure there is plenty of room between the two. or reroute the line. I assume that the gas line slits to service two carbs. If one branch is too hot and boils the gas in that branch, but the other branch is located in a cooler spot, the hot line can vapor lock while the other does not. The crap gas we get now boils at a lower temperature than the good old stuff. Be aware that just because it's new no longer means it's good. My first check would be the coil(s). I've had plenty of experience with that problem. Try temporarily hooking up a known good coil and see what the results are, if any. Electric fuel pumps --- They need to be installed as close to the tank as possible. They're great at making pressure but not very good at sucking. Never mount one in the engine compartment or put a filter on the inlet side of the pump.. Inadequate pressure promotes vapor lock.

I certainly agree with Glenn.  Running the fuel line up over the hot engine is not a good idea. The original factory configuration has the mechanical fuel pump on the front left side of the engine. There is a T on the output of the pump. One side feeds the left carb with about 1 ft long line, straight to the left carb. The factory feeds the right carb with about 4ft of line that goes down around the front of the engine (around the timing chain cover) and back up the other side.to the right carb.  The bottom of the U in the factory line however, creates a trap that can accumulate dirt and crud in the fuel system and restrict flow to the right carb.  Both ends of this line should be routinely disconnected and blown out.  I suspect that someone discovered the clogged right side fuel line problem and thought that rerouting the line upwards would eliminate that problem but as Glen suggests, may have created a new vapor lock issue.  Normally the Cadillac V12 runs fine on alcohol laced fuel because the carbs, pump and fuel lines are on the outside of the block and below exhaust manifold heat.  I suggest installing a new line like the factory line. Consider cutting the line at the bottom of the U, add a T with a removable stub pointing down, so debris will collect in the stub and keep the line clear.

There can be another problem with the fuel pump operation. the pump is operated by a push rod actuated by a lobe on the valve cam.  There is only about 1/4" of movement. The rod and the pump armature that the rod wears against can be worn down to the point that there is not sufficient movement of the pump's diaphragm to provide sufficient volume of fuel to supply both carbs at speed. It is likely that the right side will be starved for fuel due to the longer and perhaps restricted run.  I question whether the electric pump in this case would increase the volume of fuel past the mechanical pump with a worn pushrod.