Stromberg DD3 on 385ci Chrysler Imperial Straight 8

[Joao46]

Hi.

Ive been trying to set the idle mixture on this 31 Imperial Stromberg DD3.

 

Ive been told it is an odd carb in that the idle mixture screws are air screws so screwing them out leans the mixture, so I start them out about 1/2 turn out from fully closed and proceed to turn them out about 1/4 turn at a time, trying to get the idle speed to peak and the start to fall a bit. 
 

The change is subtle but by listening to the exhaust pipe I can tell the sound is now even without misfiring sounds and the engine is smooth.

 

Only issue is I’m idling at about 1000 Rpm, idle speed screw is barely touching its seat ( if I unscrew it any more it just hangs there so the butterflys are totally closed.)

 

Timing is set to basically 0 degrees and I can’t seem to find any vacuum leaks. 

Any tips? Is there any other adjustments I’m missing?

 

Thanks.

[hchris]

Maybe rotate the distributor a fraction and see if revs drop.

[hchris]

Also, any possibility the choke fast idle mechanism is holding the throttle open  ?

[edinmass]

Your idle should be set at 600-650 with a totaly warm engine. Anything higher and the gears will clash when trying to shift into first or reverse. 

[Oldtech]

You may have to pull the carb and check that the throttle plates are actually closing all the way.  If it was overhauled and someone had the shaft out they may have got the butterflys in upside down or not quite aligned. Of course, that is after all external possibilities have been checked.  The fast idle, as mentioned, also that the pedal linkage or hand throttle is not pulling it up slightly.

[PFitz]

1000 rpm is no longer idle speed.

 

With a Stromberg of that era that's up into the translon zone of idle switching over to feeding all the mix from the main jet system, so adjusting the idle screws won't show much change. Even the main jet system pulls some air through the emulsion holes in the main discharge tube that is fed from the high-speed air bleed. 

 

As Ed pointed out, your true idle speed should be lower. That is where only the idle system is feeding the mix and where adjustments to the idle air screws are the most noticeable....... that is, if the carb has been properly rebuilt. And having "properly rebuilt" carbs that early rarely happens even with many "pro" carb rebuilding shops. 

 

Paul 

[Grimy]

Fast idle can be an indication of a major vacuum leak.  I suggest you disconnect and cap the vacuum line that feeds the wiper motor(s) and see if the idle speed changes--if it does, you have a leak in the wipers themselves or their downstream lines.  Then, remove the cap and attach a vacuum gauge to the wiper feed and tell us what the reading is.  Misalignment of the throttle plates as @Oldtech says is a possibility:  look directly down the throat (engine off) and work the throttle by hand, noting whether they snap fully closed when you let go of the linkage.  How's the throttle return spring? Have you sprayed carb cleaner around the intake manifold runners?

[edinmass]

If all the channel plugs were not removed, there is NO chance that the carb will idle or adjust correctly. Maybe 1 percent of the rebuilders remove them, push through a mechanical device to clean them out, and then flush them, and replace the plugs. It's easy to ruin the carb trying to remove the plugs.......I only know of one rebuilder besides me today who pulls them EVERY time. No, I won't rebuild this unit. See photo below. Ed

 

 

 

Edited December 28, 2023 by edinmass (see edit history)

[Joao46]

Thanks for the responses.

Is there anyone out there who still rebuilds these units?

 

Aside this issue the car runs well, no bogging, engine is responsive 

 

In the meantime I’ll try to remove the wipers from the equation ensure the butterflies are closing as well as checking for vacuum leaks. 
 

On the subject of using carb cleaner to check for leaks, is there a less aggressive liquid I can use? The intakes are beautifully finished in gloss black and I’m afraid of marring the finish with carb cleaner.

 

I’ll send some pics shortly.

 

 

[Joao46]

One more question, how does one synchronize this carb’s butterflies? 
I realize it’s a 2 barrel carb that is synchronous, with each barrel feeding 4 of the 8 cylinders. 
 

Im familiar with synchronizing dual carbs on an Air Cooled VW and Triumph GT6 but these have individual throats allowing me to use a Unisyn tool. The DD3 carb’s barrels share the same opening.

Edited December 29, 2023 by Joao46 (see edit history)

[Grimy]

Just now, Joao46 said:

 

On the subject of using carb cleaner to check for leaks, is there a less aggressive liquid I can use? The intakes are beautifully finished in gloss black and I’m afraid of marring the finish with carb cleaner.

A light oil, either aerosol or squeeze bottle.  I use an enzyme-based cleaner called Oil-Eater to remove grease and oil without damaging painted surfaces.  Follow with a water soaked cloth to remove the film.

[edinmass]

Best method for checking vacuum leaks is propane. Use an unlit torch from the hardware store. You can also use it to add HC’s in the event you want to diagnose carburetor lean conditions not caused by vacuum leaks. I have an aftermarket specialty tool that has a two foot brake line on the end of a rubber hose to direct the propane to a specific point instead of the larger saturation nozzle. Hard to believe, I think I paid 12 bucks for mine in the 80’s.

 

 

Edited December 29, 2023 by edinmass (see edit history)

[edinmass]

By the way…..even if the best guy on the planet rebuilds your carb……if you don’t clean the tank, flush the lines, rebuild the fuel pump, add in an electric boost pump, and check the sending unit your just wasting time and money. Also check the tank vent, fuel pick up line, and all the fittings are passing fuel at the correct flow/volume.

[Joao46]

Isn’t it sort of unsafe to use propane near a running engine? Am I risking blowing myself up? I mean my spark plug terminals are uncovered.

[edinmass]

Zero danger…….. the rule of stoichiometry applies. There is too much air mixed with the propane to cause an explosion. It just adds hydro carbons.

[Joao46]

Here are some shots of the engine.

 

 

[Grimy]

1 hour ago, Joao46 said:

One more question, how does one synchronize this carb’s butterflies? 
I realize it’s a 2 barrel carb that is synchronous, with each barrel feeding 4 of the 8 cylinders. 
 

Im familiar with synchronizing dual carbs on an Air Cooled VW and Triumph GT6 but these have individual throats allowing me to use a Unisyn tool. The DD3 carb’s barrels share the same opening.

The butterflies also share the same shaft which keeps them aligned together.  However, you should ensure that both butterflies are oriented in same direction (but may have identical leading and trailing edges--I don't know this carb).  The mounting screws have a wee bit of wiggle room to allow for very small adjustment, but I'd remove carb to deal with them lest we drop a screw into the intake manifold and one of its runners.

[carbking]

One of the issues of synchronizing the throttle plates was the uneven wear of the original zinc alloy gears. Cannot be positive from the picture, but it appears your gears are still the original zinc. When rebuilding a DD-3 or DDR-3, the gears should be replaced with brass. Don't ask, I am sold out. Boston Gear used to have a full 360 degree gear with the exact correct diameter and pitch that could be sectioned to make both the primary and secondary gears. Primary and secondary is a misnomer, as both throttles operate simultaneously, but one is the control and the other is adjusted to the control.

 

If the gears are new, and mesh correctly, one can synchronize the throttles with the carburetor off the car by measuring the clearances of the throttle plates to throttle bores at different openings.

 

And agree with Ed, the access passage plugs must be removed so the passages can be properly cleaned.

 

Not one of the more enjoyable carbs to restore. Just one of many items with old cars that benefit with an apprentice working with a journeyman.

 

Jon

[carbking]

27 minutes ago, Grimy said:

The butterflies also share the same shaft which keeps them aligned together.  However, you should ensure that both butterflies are oriented in same direction (but may have identical leading and trailing edges--I don't know this carb).  The mounting screws have a wee bit of wiggle room to allow for very small adjustment, but I'd remove carb to deal with them lest we drop a screw into the intake manifold and one of its runners.

Actually, they do not share the same shaft. Each throttle plate has its own shaft; the shafts are connected by the use of the gears I mentioned in the post above.

 

Jon

Edited December 29, 2023 by carbking (see edit history)

[carbking]

As a point of interest (or maybe no one is interested  ), there is another downdraft two-barrel other than the Stromberg DD and DDR series made in the USA that has the parallel shafts and gears. Anyone wish to hazard a guess?

 

Jon

Edited December 29, 2023 by carbking (see edit history)

[Joao46]

17 minutes ago, carbking said:

One of the issues of synchronizing the throttle plates was the uneven wear of the original zinc alloy gears. Cannot be positive from the picture, but it appears your gears are still the original zinc. When rebuilding a DD-3 or DDR-3, the gears should be replaced with brass. Don't ask, I am sold out. Boston Gear used to have a full 360 degree gear with the exact correct diameter and pitch that could be sectioned to make both the primary and secondary gears. Primary and secondary is a misnomer, as both throttles operate simultaneously, but one is the control and the other is adjusted to the control.

 

If the gears are new, and mesh correctly, one can synchronize the throttles with the carburetor off the car by measuring the clearances of the throttle plates to throttle bores at different openings.

 

And agree with Ed, the access passage plugs must be removed so the passages can be properly cleaned.

 

Not one of the more enjoyable carbs to restore. Just one of many items with old cars that benefit with an apprentice working with a journeyman.

 

Jon

Thanks so much for the advice. As far as I can tell the gears are in good shape so i won’t mess with them. As I mentioned, the car runs well except for the high idle. 
I just went to the car and visually set the idle speed set screw to just touch so it should be at the lowest possible throttle angle. I also tweaked the screw that adjusts the backlash between the 2 gears so the slightest movement of the first barrel’s throttle shaft moves the second barrel’s shaft.

 

Again I will use propane to check for vacuum leaks and will ensure the wiper circuit is offline. 
 

Again, anyone else you can recommend that could rebuild this carb should I need it done?

[Joao46]

Well, I seem to have been successful, got it to idle at 500 rpm and got the mixture right, remembering ‘in’ is richer on the screws.

 

Thanks for all the advice.

 

next is bleeding the brakes, we just replaced all brake hoses. 
 

Are there any recommendations on front end alignment? I assume with the solid front axle we just set toe. 

[edinmass]

1 hour ago, Joao46 said:

Well, I seem to have been successful, got it to idle at 500 rpm and got the mixture right, remembering ‘in’ is richer on the screws.

 

Thanks for all the advice.

 

next is bleeding the brakes, we just replaced all brake hoses. 
 

Are there any recommendations on front end alignment? I assume with the solid front axle we just set toe. 

 

 

Nope, you need to do a proper alignment. Just about everyone who knows how to do them is 95 years old or dead. And you CAN NOT TRUST ANY SHOP TO DO IT CORRECTLY! Also, don't align it until you end up with the new tires on it.......you need to check steering box, king pins, drag link, pitman arm, and all the tie rods. Trust me....they need attention! Also springs and shackles are almost always forgotten. A proper alignment on that car today will take between 10 and 40 hours depending on your experience and set up in the shop. And do NOT use a modern alignment machine.........here is my set up on a Duesenberg.

[Joao46]

Aside from toe, what else is adjustable? 
 

How can you adjust camber on a solid axle?

And how about caster?   
 

[edinmass]

FYI

 

 

Seeing that modern fuel fitting on the carburetor already tells me whoever worked on the car last didn't know what they were doing............

[edinmass]

 

Camber shims..........

[Joao46]

Please explain to me what fitting you are referring to, and how it functions differently from the stock original part.

[edinmass]

 

Castor.......well that's another story. You need to have your new tires on it and take reading BEFORE you decide where you are headed. It's not a 2020 F150..........you need to figure out where you are before you make adjustments for modern road conditions. I set cars up using my own specifications. 

[edinmass]

 

Here is the fitting, modern. Incorrect shape and flow rate about half the original. Been there, done that. Also has a much higher friction coefficient for fuel passing through causing vapor lock under many conditions.

 

The plug or nut in the second photo is available new, and the rebuilder should have replaced it due to damage.......that tells me he doesn't work on Strombergs on a regular basis or he would have them in inventory. 

 

I would also bet the flow rate of a modern needle and seat are about 40 percent less than the original, but I have not had my hands on DD3 or a kit in over 5 years. So that's just conjecture.  

 

 

FYI- whenever I see modern fittings it's a 100 percent guarantee when I open things up, it's not gonna have been done right. 

 

 

 

 

Edited December 29, 2023 by edinmass (see edit history)

[Joao46]

10 minutes ago, edinmass said:

 

Here is the fitting, modern. Incorrect shape and flow rate about half the original. Been there, done that. Also has a much higher friction coefficient for fuel passing through causing vapor lock under many conditions.

 

The plug or nut in the second photo is available new, and the rebuilder should have replaced it due to damage.......that tells me he doesn't work on Strombergs on a regular basis or he would have them in inventory. 

 

I would also bet the flow rate of a modern needle and seat are about 40 percent less than the original, but I have not had my hands on DD3 or a kit in over 5 years. So that's just conjecture.  

 

 

FYI- whenever I see modern fittings it's a 100 percent guarantee when I open things up, it's not gonna have been done right. 

 

 

 

 

Well, apparently I can do nothing about it. No one I’ve contacted seems to have any interest in working on it nor are there any parts available for it aside a simple rebuild kit from one source.

 

The car now works well, and is responsive.

 

What choice do I have but to drive it and enjoy it?

[maok]

After a good run, check your spark plugs for a consistent latte colour, adjust mixture of required, about 15 minutes of labor time.

[Joao46]

I

3 hours ago, maok said:

After a good run, check your spark plugs for a consistent latte colour, adjust mixture of required, about 15 minutes of labor time.

Hi. I don’t think I’ve ever seen a latte color on a spark plug. Including my modern cars . 

[maok]

31 minutes ago, Joao46 said:

I

Hi. I don’t think I’ve ever seen a latte color on a spark plug. Including my modern cars . 

Latte = light brown or tan.

 

What colour do your plugs look like?

[Oldtech]

On 12/28/2023 at 7:01 PM, Joao46 said:

One more question, how does one synchronize this carb’s butterflies? 
I realize it’s a 2 barrel carb that is synchronous, with each barrel feeding 4 of the 8 cylinders. 
 

Im familiar with synchronizing dual carbs on an Air Cooled VW and Triumph GT6 but these have individual throats allowing me to use a Unisyn tool. The DD3 carb’s barrels share the same opening.

You loosen the screws holding the butterflies, make sure all idle screws are backed off and wiggle the shaft until both are firmly seated closed, then tighten the screws. 

[PFitz]

Carbking posted a copy of the sheet of info for synchronizing the carb's two barrels to get one set of four cylinders running with the same as the other four. It's done using the screw that is mounted on one of the gears. 

 

As to re-fitting the throttle plates to get a proper idle, Stromberg has a very specific position that the throttle plates have to been in in relation to the idle fuel hole in the throttle bore when the plates are fully closed. On some models the edge of the throttle plate just barely covers the idle fuel hole. On others like the U series that I work on, it has to leave a gap that needs go-no go gauges to properly measure the amount of overlap of the idle fuel hole. It is critical within a couple of thousandths of an inch.  That is why Stromberg installs one of the large brass plugs in line with those idle fuel holes so you can clearly see the overlap and check the fit. It's the brass plug, down near the carb's base and in between the two mounting flange bolt heads on that DD3. 

 

As Carbking says, "Close enough is not good enough."

 

Paul 

Edited December 30, 2023 by PFitz (see edit history)

[Joao46]

2 hours ago, PFitz said:

Carbking posted a copy of the sheet of info for synchronizing the carb's two barrels to get one set of four cylinders running with the same as the other four. It's done using the screw that is mounted on one of the gears. 

 

As to re-fitting the throttle plates to get a proper idle, Stromberg has a very specific position that the throttle plates have to been in in relation to the idle fuel hole in the throttle bore when the plates are fully closed. On some models the edge of the throttle plate just barely covers the idle fuel hole. On others like the U series that I work on, it has to leave a gap that needs go-no go gauges to properly measure the amount of overlap of the idle fuel hole. It is critical within a couple of thousandths of an inch.  That is why Stromberg installs one of the large brass plugs in line with those idle fuel holes so you can clearly see the overlap and check the fit. It's the brass plug, down near the carb's base and in between the two mounting flange bolt heads on that DD3. 

 

As Carbking says, "Close enough is not good enough."

 

Paul 

Where is this post you mention?

 

Also. Would it be advisable to remove the carb top cover to measure the float level? Which screws should  I remove? 
 

Im just afraid of breaking anything 

[PFitz]

2 hours ago, Joao46 said:

Where is this post you mention?

 

Also. Would it be advisable to remove the carb top cover to measure the float level? Which screws should  I remove? 
 

Im just afraid of breaking anything 

Scroll back up 18 posts. It's that big yellow spot with two cutaway pictures of the carb and lots of printed instructions on it. Right click, download to your computer and read. It will tell you how to do all the adjustments and where - including the float level.

 

Paul

[edinmass]

Joao46…….your afraid of breaking something……..good for you. Extra caution is a MUST on ANY pre war carb. Removing the incorrect fitting could cause disaster………..it takes a craftsman’s hands to know what will or will not crack a casting or strip out threads. In one of your comments you said it’s running good now. With all due respect, if you haven’t driven a half dozen similar Chryslers…….thats a statement that is hard to grasp from either side. I have driven about a dozen of them. The are exceptionally fine automobiles and I would own one if the right deal came across the desk. I don’t hunt them, and thus far haven’t tripped over an offering that would make me pull the trigger. They are as every bit as good as a Packard Super Eight, big Pierce Arrow, and other similar cars. Where are you located? I get around quite a bit. It would be fun to stop by and visit with you and your car. Ed 

[Joao46]

Hi. The car is my dad’s and he lives in the Philadelphia area.

 

Im helping him work on it.

 

One thing I’d like to do is to check the float level. But dad tried to remove the top 5 screws. There are 2 large ones and 3 small ones to lift the cover but it seemed to still be held down. Not wanting to force anything, he gave up and retightened them.

 

The main concern in doing anything with this carb is the age. 
 

As far as ability dad is quite familiar with carburetors, having rebuilt the pair of Holleys in his 57 TBird and tuned them so the car runs pretty close to perfect.

 

 

[Oldtech]

My advice on setting the throttle butterflies is wrong for this carb.  Ignore!. As usual Carb King knows!!