The Daimler was stalling. I pulled of the intake caps off both SUD bowls and checked the valve arms and the pulled the floats. One bowl, the driver's side, was filled with orange gunk the viscosity of petroleum jelly. I clean it all out with carb cleaner and a rag, and also the passenger side bowl. Then I put Berryman's Clean in both bowls, and let it sit over night.

I filled up both bowls with gasoline. The car started and ran fine and strong but eventually stalled. Engine idling at 10 RPMs. (See pics of meter readings... ) But only the passenger side drained into the SUD while the bowl with the now-removed orange gunk didn't drain at all.

I drained and repeated the Berryman's Cleaner. I was working better, but now the previously clogged bowl only drained into the SUD about half as much as the passengerside bowl ( So a 2:1 uneven ratio )

SO short of removing entire SUD unit and disassembling and cleaning, what are your suggestions?

I don't want to stick wire into the hole/port or the bowl for concern of puncturing something further inside the SUD. But the cleaners are getting all the way inside to whatever is causing the clog....

 

EDIT: And for whatever it is worth, I have the car up on floorjacks. I was told this is a beneficial action as it takes weight off the suspension.

I put the car into gear and the right wheel was turning over nicely with new gear oil, the engine ran strong until stalling from lack of gas, and the RPMs idled continually at 10. So overall, it is okay except for the clogged hole in one bowl.

 

"Orange Gunk" _ old gas with Ethanol maybe ? You must live in the US...
Try this.
Remove the vacuum piston chamber covers (3 screws on each carb)
Pull out the piston (be carful not do damage the needle jet)
The hole that you see in the carb after the needle is removed connects directly to the bottom of each float bowl (or the SUD bowls as you call them)

Take something like WD40 or carb cleaner with the long plastic extension from the spray nozzle and inset it into the hole where the needle was.
The cleaning properties and the force of the spray should clean out the gunk in that area.
You should see the spray come out of the bottom of the float bowl once the fuel path is clear.

 

When you say draining, do you mean not filling up, or not emptying ?

If it's not filling, then the inlet is blocked, if you have cut off the fuel and run the engine with the bowls manually filled and when it cuts out one bowl is still full then the jets are blocked. If there is old fuel in the system this need clearing out otherwise you will keep getting the same issue until the lines are all clear.

 

So the SUD carburetor still has issues with the gas flow, though it has gotten a bit better.
Here are pics of the fuel filter leading into both float bowls.
I'm noting bits of what looks like rust in the clear, plastic filter.
Thank you, plastic!
I has shown me what is coimg thru the fuel line!

I look at the orange filter itself and do not see anything, so the filter and the angle of the filter appear to have kept the non-liquid crud out.
But the filter will be changed anyway just to be safe.

 

Great advise. Did exactly that.
I removed all three screws and pulled off the dome.
The dome came off with a long spring
I then slowly and carefully pulled out a hollow cylinder that had the fragile needle I've heard so much of.

Looking inside the now vacant housing, I see a brass "bullseye" centered in the carburetor. ( pic 1)
Berryman's B-12 cleaner with a long, ridged tube was inserted into the port located in back of the float bowl ( Pic 2) and sprayed.
( Somewhat discernible in the picture. Look for the black dot in the back of the float bowl )

A bit of a jet of the B-12 fluid squirted out the bullseye. I saw a fleck of the orange gunk come out. It and another bit of the orange junk was wiped from the interior area.

Before replacing the hollowed cylinder, it was cleaned with B-12 ( Pic 3)
It was gently reinserted back into the housing. The ridge guide was a huge help in assuring proper placement. ( Pic 4)

Before replacing the dome and the long spring, it, too, was sprayed and cleaned before being placed over the rod extension and screwed back into place.
I think I did everything correctly.
Next to test it with gasoline.

 

I filled up both float bowls manually by pouring gas inside ach.
Both were filled to the same levels, and neither had the floats inside nor the caps on.

The engine started and ran nicely.
But once again, one float bowl emptied while the other still held gas.
The engine stopped when one float bowl emptied completely.
This was repeated with the same outcomes two more occasions.

So I'm not sure what's the issue and how to address.
It seems illogical after the B-12 squirted clear from the brass bullseye.

I would be grateful if could explain the process of:

* How the liquid gas goes from the float bowl through the inlet hole in back of the float bowl and how it get through the brass bullseye piece?
( Is the gas still in its liquid state at that point? )

* Does the gasoline become vapor in the dome or elsewhere?

* Exactly what happens once the gas is in this area, and how does it ultimately get into the pistons for combustion?

Many thanks for educating me!
I truly find the SUD unit fascinating!

 

It's filling both bowls.
One bowls empty as it should. The other does not.

 

@1964Daimler
One float bowl will always empty first because that is the one feeding the external choke on that carburetor (I'm assuming that your car has the electric choke mounted off the front carb).
Once "that" bowl is emptied of fuel, the car will stall as there will be no more fuel being supplied to the choke.
A cold engine with SU carbs will simply not run with out it being choked _ or enriched if you like.

That "bulls eye" as you call it, is the main venturi of the SU carburetor. The tapered needle controls how much fuel flows out of the venturi jet depending how far the butterfly valves are open.
The more the butterfly valve opens, the higher the piston is raised and more fuel and air flows into the engine.
The butterfly valves are controlled by your foot on the accelerator pedal.

If you look at the throat of the carburetors, you will notice that it's narrowed right where the bulls eye is, there's a ramp leading up to the bulls eye and then down again as it leaves the carb.
When the piston travels down in the engine on intake (the intake valve is open at this point) atmosphere flows into the engine ( the atmosphere weighs around 15.4 lbs. per square inch at sea level _ it's heavy).
For atmosphere to flow into the engine, your foot also has to open the butterfly valve.
As atmosphere flows through the carb, it also picks up fuel through the bulls eye and depending how much the butter fly valve is open, the more or less fuel and air flows into the engine.
It's how a venturi works, the narrowed part of the carb where the ramps are, creates a drop in air pressure (less the 15.4 lbs per square inch) and the fuel flows from the bottom of each float bowl through the bulls eye into the engine upon the "intake" cycle.
This action also introduces air with the fuel so it vaporizes properly and burns on ignition and compression on that cycle with in the engine _ it's know as the compression/combustion cycle.

When I talk about flow of atmosphere, people perceive that as engine vacuum, that vacuum on an SU carb, also raises the pistons that control that fragile tapered needle. Engine vacuum flows through those two small holes at the bottom of the piston, raising the piston. The piston is raised or lowered depending on how far the butterfly valves are open. You will notice that the needle is tapered _ what that is doing is controlling the amount of gas going into the engine.
A larger engine will have a larger bulls eye and/or a thinner taper to allow more fuel into the engine.

Bit of a crash course on how a carb works.
North American carbs work on the same principal, but instead of having one jet that is metered by the piston and tapered needle, an American carburetor has many different "fixed" venturis with in the throat of the carb.
Each venturi comes into play as the butterfly valve is opened further and further.
A North American carb is far more complicated than a simple SU with all it's different venturi sizes with in the throat of the carb.

I always found it funny how a North American mechanics gasp in horror of the site of SU crabs, for if they truly understood how a carb works, they wouldn't be so frightened of them.

Google "venturi" and "and carburetor.

 

Take a look at these

Introduction - SU Carburetters

HD Diaphragm Jet Type Carburetter and Auxiliary Enrichment Carburetter - SU Carburetters

This will help put Jeff's explanation into pictures. You will see that the fuel level in the float chamber is equal to the level of the jet, this is where the fuel level in the float chamber comes into play, if it is too high it will flow into the intake side (although slowly) causing high fuel / air mixture (too rich)

Jeff - The description of atmosphere I find a little misleading personally , everything is subject to atmospheric pressure, so in order for air to flow one way or another, something has to be increased or lowered relative to atmospheric pressure (this is absolute pressure) so either there has to be a pressure lower than atmospheric pressure in the cylinder (vacuum or at least relative to atmosphere) or increased pressure in the carb.
The intake stroke is what pulls the air into the carb not the atmospheric pressure pushing it in. This is where "atmosphere flows through " should IMO read "atmosphere is drawn through" I know it sounds a little pedantic, but I think it's easier to understand personally.

 

Yes, that's one way of looking at it, but my explanation as to how atmosphere and it's relation to the intake stroke, I find easier to understand.
I didn't necessarily say atmospheric pressure was being pushed into the engine, I said it flows into the engine, but if you want me to say "drawn" through _ sure, why not.
Atmosphere fills the void as the piston travels downward on the intake stroke.
Just like if you took a syringe and pulled on it with you finger over the end and then suddenly took your finger off _ air (or atmospheric pressure) rushes in to fill the empty space inside the syringe.

This is why carbureted engines don't work very well at high altitudes, there's less atmospheric pressure (not 15.4 lbs per square inch anymore, we're not at sea level now).
With less air flowing into the void as the engine piston travels downward, less fuel is picked up through the carburetor causing lean conditions and over heating.
The venturi action of the carburetor becomes less efficient at high altitudes.

 

Jeff I fully agree, it's that potato potaato thing, 2 different ways of the describing the same thing.

I have to disagree re the altitude issue, the engine becomes richer not leaner, there is less oxygen molecules at high altitude, and also as you say less pressure, but the resultant fuel mixture ends up richer, that is why a leaner mixing needle is recommended for high altitude living cars with an SU carb.
There is also issue in the float bowl with less atm pressure, the float chamber level rises slightly also causing richer mixture, you can even get float distortion at really high altitudes, that may have been a factor in Daimler1964's issue with the fractured float ?

 

Yes, you're right about the altitude thing, had to refresh my memory on that one.
That would also explain the cracked float too.
I wonder how much less outside pressure it would take to crack brass float ?
Maybe it was driven in the Himalayas...
Or maybe at one point water entered and froze in the float bowl.

 

It would have 10psi pressure difference on top of Everest, can't even see that doing it!

The float would also have sunk like a stone on the drive back down too if we apply our physics !!!!


Now we know where the orange gunk came from, well know fact at high altitude

The frozen bowl could be a much better answer Jeff

 

Correct, JeffR1!
I've actually brought the SU carburetor to local carburetor specialists, and they refuse to work on the SU. They shake their heads vigorously and say to go to a Jaguar specialist.
( Actually, I did exactly that and brought the SU to a local Jaguar dealership. The repair technicians never had seen one, and these kids parents weren't born before 1960. )


One mechanic crossed his fingers in a mock vampire crucifix and said Jaguars are the devil.


My next posting is why I am grateful for the forum and all those who contribute their knowledge, insights, and experiences.

 

Here is a great place to go, Z Therapy, they specialize in rebuilding SU carburetors and this is way better than a DIY rebuild kit as they rebuild every nut and bolt and many items not available on any rebuild kit. They are the place to go for all Datsun SU's and they can do your Jag SU's; well worth the money.

 

"One mechanic crossed his fingers in a mock vampire crucifix and said Jaguars are the devil."

Unless you can do it yourself, he trick is finding a mechanic that really knows how to work on the cars, and then taking their advice.


It is great that we have resources like Z therapy. I am hoping that my home carb rebuild will do the trick, but I know if I have problems with how the car is running, you can bet I'm going to yank them out and send them off for some professional attention!

 

Theses guys here have complete rebuild kits.

The Worlds Sole Manufacturer of Genuine SU Parts - SU Carburetters

What goes wrong with SU's is the wear at the bushings and butterfly shaft that occurs there.
Badly worn bushings creates a vacuum leak.

The only other moving part is the main piston that controls air/mixture flow.
The piston gets lubricated when one tops up the damper tubes, so very little wear, if any, occurs here.

 

I have had Datsun SU's rebuilt with kits but they never run like having them completely rebuilt professionally. SU's are great carbs as both Datsun's and Jags can still run on 40 year old + SU's which is impressive but their is a huge difference when they are rebuilt better than new.


At places like Z Therapy they actually make ball-bearing throttle shafts! They take the carbs and everything is fully replated, using the most expensive and durable process available. They don't plastic bead the bodies and sell them. They machine polish them to restore the factory shine. They also make their our own nozzles for closer tolerances and fix sticky pistons. Every part of the carb is treated like it is the most important part. Carbs and parts are covered by a 3 year warranty. If carb cleaner and silicone spray lube don't fix it, they will! Exchange and same day service standard (customer pays shipping). How many SU "rebuilders" engrave serial numbers on the throttle shafts? Z Therapy does...

 

So I did the unthinkable: I disassembled the SU Carburetor!


With more frustration than fear, the SU was removed from the manifold.
The entire unit was put inside a small box.
( I was lectured that a carburetor should always be disassembled in a pizza box as not to lose its small parts. Good advise. )


I first took off the dome and removed the long spring in the interior. Everything was clean.


Next, the bottom half was disassembled, starting with the four long screws.
Now the apparent problem was clear:


The jet area of the plastic diaphragm was clogged with dried gunk!


It was the same yellow stuff that was removed previously. Now it was cakey, and there was even some residual on the float and in the port "tunnel" connection from the float bowl into the jet diaphragm.


A soft toothbrush removed the yellow crud from the diaphragm and the bowl. Everything was cleaned with some gas, and all bits of the yellow gunk removed.


The SU was reassembled, with amazing ease! As this was done, I finally understood what I was told by those in the know -- including Mr. Mop Hawker --- that the SU is a simple yet powerful carburetor.


What I cannot understand is why the cakey yellow gunk formed on this one SU and not the other. ( Granted, this is the first SU that received gasoline from the fuel line before the connection to the second SU on the other side. ) But why just one side?


And I replaced both gaskets that rest atop each float bowl.