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sounds to simple but i would also check the spark plugs, if they have any buildup or just plain bad they won't allow enough spark to come through, as well as checking your plug wires.....if this doesn't help, check and make sure that your coil and plug wires are not arcing around on top of your distributor cap. you may have to get it dark enough to see if you have arcing

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OK reading back over the postings I see you have :

1. cleared the fuel line from tank to engine

2. replaced the fuel pump(s)

3. changed the coil and distributor

4. checked ignition timing

I dont see where the plugs or spark leads have been changed ?

And then we are entering the realm of obscure faults :

1.Can you replace the distributor cap to eliminate cross firing?

2.Change the carb?

3.Connect a timing light, make a mark on the front pulley and watch the behaviour of the spark as you take the engine up and down the rev range. You should be seeing an even rhythmic flash of the strobe all through the rev range and the pulley mark should progressively move forward and back as engine speed changes.

In all of this am I right in saying that from a cold start the engine behaves normally and only breaks down after a mile or two on the road at normal traffic speeds ??

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I know I haven't had time to check all of the items that have been generously suggested so far, but here are a few things that have been further down the list because they were done by the previous owner within the year prior to my buying the car last May:

1. New plugs (which were perfect the two times I've since checked them).

2. New ignition wire harness, including the coil to distributor lead.

3. New distributor cap, which I cleaned last week (I have a NOS one I can swap).

4. New points, which I cleaned last week (I have a new set I can swap out).

5. Timing.

6. Had the carb professionally rebuilt.

7. Cleaned and sealed the gas tank and blew out the fuel lines.

8. Had the mechanical fuel pump professionally rebuilt.

9. Air filter cleaned.

Some of those still need double checking, though. I have a 12-volt timing light which I can hitch up to one of my newer cars.

I haven't blown out the fuel lines, but after I put in the electric pump, I ran it with the fuel line in a bottle and it seemed to be putting out more than what the carb could use.

Actually, she runs VERY smoothly when cold, at idle when warming up, and at lower speeds when warmed up and the choke is in. When I warm her up, take her out for a test drive, accelerate briskly through first and second, shift into third at about 30 mph, and continue to push it a little faster, she soon begins stumbling...like it's just not getting enough gas. If I back off, push the clutch in, and coast while feathering the gas...or just pull over for a minute, she'll run smoothly again until I start accelerating again. That's why I get the feeling that somehow the carb isn't delivering enough gas when it's needed. (Faulty accelerator pump? Blocked needle valve? Float issue?) But, so far, that's just a feeling.

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Phil...are you by chance still running the spark plug wires through the usual steel tube type harness? Sometimes these have a tendency to short out the wires. I have run across the problem with my '31s.

Yes, John, the metal tube is in use. If that were shorting, would it affect performance at ALL speeds or just higher loads, faster revs on the engine? Would you be able to observe the shorting in the dark?

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In all of this it seems the problem has recently developed; does the misfire persist when you pull off the road and rev the engine ??

Have you had the top off the carb ? is there some muck floating around under inertia in the carb bowl blocking jets ? can you replace the complete carb to eliminate it ?

And moving to more obscure items; what about ensuring all the intake manifold bolts are tight or any other possibility of intake manifold leak.

Do you have access to a vacuum guage? one of these hooked into the intake manifold should enable you to source a vac. leak as well as valve timing / leak issues, I`m thinking along the lines of stretched timing chain causing valve timing to go off as engine warms up; what age / mileage is the engine ?

Getting back to 12v timing light, if it requires 12v input, you can use it on 6v by connecting it with jumper leads to a 12v battery.

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hchris mentioned a manifold leak...did you ever feel around the inboard side of the manifold to check for that possible hole I mentioned earlier? Won't be easy to find, but I would think that your car would have it as mine does.

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hchris mentioned a manifold leak...did you ever feel around the inboard side of the manifold to check for that possible hole I mentioned earlier? Won't be easy to find, but I would think that your car would have it as mine does.

From what I read, this only occurs when the engine warms up so a permanent hole in the inlet manifold would presumably cause a problem right from start up; I was thinking more along the lines of the manifold moving as engine heats up.

In any case if its intake manifold related a vacuum guage will show this up.

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John...see post #39 for my comments on the manifold "hole."

I'll double check whether the stumbling & popping occur reving the engine at the side of the road, but I'm betting not.

I've held off cracking open the carb until I tried some of the easier stuff...particularly the electrical components. I could swap out the carb on my original DL6, although that hasn't been run for several years and might need some de-gumming first. BTW, what are the opinions about using carb cleaners?

I concur that the situation has been coming on for awhile, as it was driving fine when I got it in May.

The engine has only 47K original miles on it...barely broken in!

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The old wax paper condensers had a half life of about 15 years in other words half of them would fail after that time. Practically all of them from the 30s thru the 50s are now junk even ones that have never been installed (NOS). This is common knowledge in the old radio hobby.

The new milar jobs are far superior and will last practically indefinitely. If you can't find the condenser you need, get one from an electronic supply. They call them capacitors.

You will have to add the connector on the end of the wire, use the one off your old condenser.

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On the gas question, modern 87 octane is too high. Your car will run better if you cut the gas with kerosene. Try 1 part kerosene to 6 parts gas. I know some guys go up to 1 to 3.

Your engine was made to run on around 50 to 60 octane. The octane should look like the compression ratio. In other words, a modern hi perf motor with 9.2:1 compression, give it hi test 92 octane. A regular low compression, 8.7:1 motor 87 octane regular. A 6:1 flathead 60 octane etc.

Naturally this is not an exact rule but fairly close.

I doubt this is your problem but what the heck it can't hurt to try. Others report easier starting, cooler running and more power. Cuts the chance of vapor lock too.

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Plug gaps have stayed perfect since before this problem arose, and the two condensers I've installed are both brand new modern types. The gasoline/kerosene mix advice is interesting and worth a try.

But the talk of checking for a vacuum leak switched on a lightbulb in my head, adding something new to investigate. This car has the rather rare optional (on a Dodge anyway...standard on a Chrysler, I believe) Automatic Clutch Control...introduced in 1932, if memory serves me right. My first DL does not have one, so I am totally ignorant of how it works...even IF it's working at all since the Freewheeling isn't! The DB owner's manual has nothing on it, but fortunately, the 13th edition of the Dyke's Encyclopedia has an impressive 3-page entry in the Addenda. The diagrams show a network of vacuum lines off the intake manifold, so that got me thinking that I really need to bone up on that system.

Anybody out there have any experience with those Auto Clutch units?

I'm reposting the photo of the right side of the engine to bring attention to all of the "spaghetti" for the Auto Clutch coming off the intake manifold just above the fuel pump. That large gray "can" just aft of the air intake silencer is also part of the system.

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Edited by Phil 32DL6 (see edit history)
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Well the vacuum clutch mechanism is similar to a power brake booster unit in that it relieves the work load on the pedal as you depress the clutch.

Its power source is the vacuum from the inlet manifold which acts as you close the throttle, which is obviously what you do when changing gears. There is also an internal pendulum mechanism which senses acceleration / deceleration and varies the vacuum accordingly.

You should have a control cable located under the dash which allows you to select it off or on;

most people these days would leave it off. In modern traffic flows its a bit of a trap as every time you lift your foot off the throttle it will push the clutch in for you and you finish up freewheeling, somewhat unnerving when in a line of stop start traffic.

As far as influencing your engine, yes it could be a source of vacuum leak, no more or less than a number of other things. As I said earlier if you can put a vacuum guage on the inlet manifold you can at least establish or eliminate this as a source of problems.

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You should have a control cable located under the dash which allows you to select it off or on...

I believe the Auto Clutch works off the Freewheeling control knob on the dash, but, since the Freewheeling doesn't work right, I've got it disengaged...thus no Auto Clutch. I'm not missing it.

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Edited by Phil 32DL6 (see edit history)
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I would get out the boat tank and eliminate the tank, and lines. If you have a primer bulb it would be another bonus as you could apply additional pressure by hand. It sounds like you could have some junk in the tank that takes a minute to plug the pick up.

Make friends with the guy at that place that it quits. Then you might be able to do your trouble shooting in both directions.

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I know I've got a bunch of you avid problem solvers champing at the bit for every ort of info, but I have to prolong the agony just a little longer. My business workload picked up (yea!), Fall yard work picked up (boo!), and my wife brought a new, high-maintenance kitten into our life (isn't that the lamest excuse you've ever heard?!). Oh, and you know, it's World Series time, guys!

My next step is to take that Auto Clutch vacuum line out of play by sealing off the intake manifold port. Since my first DL is lacking that optional contraption, it has a factory-made metal plate creating the seal. I just squirted some parts-ease fluid on its mounting bolts so it'll come off no sweat in a few days.

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Well...it wasn't a vacuum leak in the Auto Clutch gizmo. (Rats!)

I unbolted Auto Clutch line from the flange on the intake manifold, slipped in a solid plate from the other DL to seal the hole, and reassembled.

Warmed her up, drove down the street and, sure enough, soon after putting her in third gear, she began to sputter next to "that certain house."

The hunt goes on...

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What cures it so you can drive home? Let it sit? How long? Bump here or there? Do you drive it home stumbling? Des it ever shut off while stumbling? IS this house on a grade differant from the rest of the drive? We are going to fix this thing or break it, one or the other!! My '24 had problems with spark, but it was occational. It was the headlight/ignition switch. Inside there are contacts that connect to differant posts for differant purposes, lights, dash light, etc. The contacts are brass and the insulator is a hard paper type stuff. There were tracks from the brass connecting sevral posts JUST enough that under the right situation { like when the wife was along} I would lose ignition. I used an ink erasor to clean the tracks off, haven't had a problem since. Look in STUPID places for the problem!!

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The road when I'm test driving is perfectly flat. Actually all I have to do is slow down...back off on the acceleration. It never actually quits, it just acts like it's about to...like the tank is empty. Pushing in the clutch and coasting 50 feet while lightly feathering the gas pedal helps keep the engine running, and I can then drive slowly, say 25 mph without stumbling. But, if I try to accelerate back up to 35 mph or so, it will start hesitating again.

That's why I get the sensation that either not enough gas is getting into or out of the carb (for any of many reason), or the mixture is too lean (for whatever reason, such as an air leak before or after the carb).

While I've blocked off the Auto Clutch vacuum line, I'm going to check (or disconnect) the somewhat complicated linkages between the Auto Clutch and the carb to see if something funny is going on there. After that, I should probably switch carbs and see what happens.

Edited by Phil 32DL6 (see edit history)
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Sounds just like a car I had. 1949 Dodge. Would run great for a few miles and then crap out. I found out after I sold the car that it was the coil heating up. It would cool off after stopping for a few minutes and then crap out again. I know that you have replaced the coil, but you might try another, just in case.

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  • 2 weeks later...

So...today I removed the carb, and replaced it with the one from my other DL. (Which, by the way has been sitting unused for seven years!) Being identical Carter BB1s, you'd think that ANY difference in performance would be attributable to such variable conditions as something sticking or blocked up, etc. Right?

Well, she fired right up and after a good warm up, off we went accelerating down the street. Opposite the fateful house...cough, cough, choke. No change in the stumbling whatsoever.

I have to stay positive and keep telling myself that "eliminating possible causes IS progress..."

Next up, search for vacuum leaks, check compression, fuel pump pressure, recheck timing...

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Agreed...but I've already installed an electric fuel pump which seems to be functioning properly (I've got a pressure gauge on order to confirm that), plus I was running it in-line with the mechanical pump for a while. The mechanical pump has since been by-passed without any effect. The only fuel filter is the metal one in the bottom of the electric pump and I flushed that really well in kerosine when I installed it. The flexible fuel line is brand new and has gentle curves.

Has anyone tried checking for intake manifold leaks by spraying the seams with a volatile fluid like DW-40 while the engine is idling and listening for an increase in RPM? I read that somewhere.

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