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Lisa P

1931 With Stromberg U-3 Runs Too Rich

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The Stromberg U-3 on the Franklin I've been working on runs way too rich. My mechanic mentor and myself are at a loss and thought we should ask for some advice. We can turn the Air/Idle adjusting screw all the way in and all the way out and there is no variation in the way the car idles. We have also checked for vacuum leaks and cannot find any. Could we be missing something on the carburetor? The carb was professionally rebuilt prior to installation on the car. Any ideas would be greatly appreciated. Thanks.

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iS THERE A THREADED WHOLE FOR A VACUUM LINE WHERE A LINE WOULD GO TO A VACUUM ADVANCE? I didn't know about it at first (Cat likes the walk on my keyboard)

Mine was running very rich (Popping out The Carb)and the idle adjustment screw made no difference. I had blocked a hole in the base of the carb with a gasket.I drilled it out and now have idle agjustmenmt.

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Dwight, not that I'm aware of, but I will check that tomorrow! Thanks for your input.

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Lisa -

Does the car run rich all the time?

Black smoke out the tailpipe?

Doesn't develop full power, stumbles and smokes?

Pulling the choke out while driving only makes things worse, never better?

Assuming it is rich all the time; realize that the idle screw is a very fine tune of idle only. It cannot correct any other problems. My suggestion is to open it 1/2-3/4 turn from closed and check other things. Once the car runs great at all other conditions, then fine-tune the idle. And remember it is backward from many other idle mixture screws: turning in =richer idle mixture and turning out = leaner.

Reasons a U-3 carb may run rich:

Float level too high

Fuel pressure to high

Sticky float valve

Leaky float valve

Float heavy or leaking

Main jet too big

Economizer malfunctioning, causing economizer valve to open early or stay open

choke butterfly not fully opening

other?

A professional rebuild does not always mean there might not be a glitch inside, so all should be suspect. Start with the simple things and check all.

let us know -

Tom Rasmussen

Sent from my iPad

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Lisa -

Does the car run rich all the time?

Black smoke out the tailpipe?

Doesn't develop full power, stumbles and smokes?

Pulling the choke out while driving only makes things worse, never better?

In response to your questions, yes to all. It does run rich all the time. There is plenty of black soot, not just smoke, coming from the tailpipe. It is a loping idle, will backfire through the carburetor or the tailpipe when you try to accelerate. Pulling out the choke will make it idle more quickly, but any attempt at acceleration will make it stumble, backfire, and almost always die.

I have checked the valve clearance while the car is very hot, and when it is cold. There aren't any valves hanging open.

We've checked timing.

We've checked for intake or vacuum leaks.

I've replaced the coil, plug wires, and plugs (and filed and set the points).

The fuel pump was rebuilt but I've not checked output pressure yet. Should it be between 3-5?

And, I have fiddled with the float level and there seems to be no difference in how the car runs.

The car did run very, very nice one time when it was running out of gas. My mentor suggested that this was because it was a lean condition and that the carburetor needs to be adjusted to replicate that condition. As it sits, we get no response from the air idle adjustment.

Paul Fitz has recommended that he take a look at the carb to make sure that the rebuilders didn't miss anything. I believe we will go that route rather than chasing our tails. Thanks so much for all the help, I truly appreciate it and hope I can contribute something to the forum someday.

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Have you compression checked the engine? If not I would suggest that to rule out intake valve problems.

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Lisa- good move to dig into the carb. It sounds like it could be a faulty economizer. It is an unusual feature not always understood by carb rebuilders. Paul will certainly let you know if the fault is in the carb.

And please follow up with the group. Sharing results helps us all.

Good luck!

tom

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Lisa,

Did you ever get things resolved? The reason I am asking is I have a 1930 Franklin that runs very rich as well as also does not develop full power. It however has a Carter BB-1 carb.

Thanks,

Bill

Edited by Bill Jewell (see edit history)

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Lisa,

Did you ever get things resolved? The reason I am asking is I have a 1930 Franklin that runs very rich as well as also does not develop full power. It however has a Carter BB-1 carb.

Thanks,

Bill

Hi Bill -

Most Carter BB-1 carbs have an adjustable main jet. Have you attempted a main jet adjustment?

tom

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Hi Tom,

It does indeed have a main jet adjustment. To make the mixture less rich would I screw it inward (clockwise) or outward (counter clockwise)?

Thank you for your help!

Bill Jewell

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Yup. I'll bet you'll get it dialed in!

tom

Sorry - I meant to say in for lean out for rich.

Tom

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Update from Paul regarding the Stromberg. He has found no less than 17 things wrong with the carb. As Tom suspected, the economizer was totally wrong. The original had been removed and replaced with an oversized tube. Also, the main discharge jet was never removed and cleaned. These are only some of the items found by Paul. His knowledge of these carburetors far surpasses that of the past rebuilders!

Here is Paul's list, and he cautions that we cannot be certain who is responsible for the items that were wrong:

1. Throttle return spring was too short and fastened in the wrong position. It should be a longer spring (long-tailed NAPA throttle return spring close to original) that goes from the motor side throttle lever arm, back and hooks into a 1/8 inch hole in the top edge of the sheet metal holder of the felt dust seal that the brake pedal rod goes through on the fire wall. See picture attached.

2. Economizer syringe not original and way too over-sized to seal around the econo piston.

3. Spring cup missing from top of econo piston.

4. Sealing washers missing from top of econo syringe - inside and out - and bottom of econo piston.

Replaced entire economizer syringe with a rebuilt one.

5. Economizer valve and seat faces eroded and couldn’t seal fuel leakage. Lapped faces to get proper seal.

6. Econo sleeve nut loose with screw slot chewed up.

7. Bowl gasket made out of exhaust manifold material. Made new one with correct Velmoid gasket material.

8. Three bowl screws missing lock washers. Installed new lock washers.

9. Original pot metal venturi still in place, showing usual cracking/chipping of upper edge. Replaced with aluminum reproduction.

10. Float level low and float pin bent. Float tested good for no leaks. Replaced pin.

11. Float needle tip eroded and couldn’t seal. Reground tip to seal properly.

12. Main discharge jet never removed and cleaned. Did so and installed new gasket.

13. Float level low. Re-set to approximate 9/16 inch.

14. Accelerator bell squashed out of round. Re-shaped.

15. Accelerator valve screw slot chewed up. Valve was removed and damaged by using pliers. Filed off burrs and lapped valve faces to seal properly.

16. High speed air bleed in wrong hole (lower). Was soldered shut. Being that it was below float level, to prevent fuel leakage ? Removed and installed in upper hole after drilling out incorrect screw plug in upper hole. Made new screw plug for lower hole.

17. Copper spark plug washer used for fuel inlet fitting seat gasket – over pieces of stuck-on original gasket. Cleaned off old gasket pieces and taped a new gasket to seat.

18. On Strombergs of this era the cast iron parts were paint gloss black, with cadmium plated steel parts – like second picture attached. Not all black oxide finish.

Bill, did you sort out your Franklin/Carter carb?

Lisa

Edited by Lisa P
Additional information added (see edit history)

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Lisa, thanks for the update. Lots of us Franklin owners learn a lot of valuable information from reading these threads. Especially when solutions are posted.

And thanks to all the Franklin owners willing to share their knowledge.

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I would also like to add my thanks to all who participated in this discussion. I am sure many of us U-3 users learned something from this. I encourage everyone to participate and ask questions. You can be sure others have the same questions you have and we all learn from each others experience.

I used to tell my Engineers during their training" We were not born knowing the answer, we have to acquire knowledge by asking, reading ,watching, and trial end error.

Never be afraid to ask"

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HI Lisa,

I did adjust my Carter BB-1 carburetor to be more lean, however, it is still not running as well as it should. I am going to look for an original Stromberg U-3 carburetor. Is your 31 Franklin running well now?

Thanks!

Bill Jewell

Arlington, Texas

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HI Lisa,

I did adjust my Carter BB-1 carburetor to be more lean, however, it is still not running as well as it should. I am going to look for an original Stromberg U-3 carburetor. Is your 31 Franklin running well now?

Thanks!

Bill Jewell

Arlington, Texas

Bill, I just installed the carburetor on the Franklin and am happy to say that the difference is amazing. Where there had been stumbling, loping and black smoke I now have a smooth and responsive engine. I still have to check the float level, but thanks to Paul, the car now runs as it should.

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Hi Lisa,

Have you heard from Paul Fitzpatrick recently? He is rebuilding a Stromberg U-3 carburetor for me and I have not heard from him for over 2 months. I have tried to email him and call him and get no response.

Thanks!

Bill Jewell

817-739-8565

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Lisa,

Were you able to attach a picture of the throttle return spring attachment on your car?

I do not see the picture referred to in your post.

Thank you,

Jim

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