OK, page 21, that still leaves some 49 threads on page 21 to go through, care to leave a specific link to which thread please ?
The cars enrichment carburetor can still have fuel over-flow problems even though the choke is not energized on a very hot day and the engine is fully warmed up _ it does not have to be on, in fact it is quite common for it to give the problem you're having.

Yes, I thought you meant heater box, but now I'm really confused, no air intake in a 340 is attached to the firewall that requires a bent wrench for removal.
There should be a pancake style air cleaner that is connected to the planum chamber through a large rubber type connection piece _ it looks like a large heavy wide rubber band.
The plenum is easily removed with a 1/2 inch wrench, there is just enough room to get a box end spanner at the back bolt closest to the firewall, there is no need for a bent wrench, the wrench that I have is already angled from the factory.
The box end spanner has to be ground down to get it in there. (like in my photo), but that's it.

I need a link to the thread on page 21, and maybe a photo of what you're talking about.

I had to look up Boffin.

Or maybe you mean at the firewall, which means closest to the firewall ?

The spanner (wrench) will also just clear the float bowl, at least mine does.
Grind it down if need be.
What appears to be inside bolts are not bolts, they are just alignment guides, you mentioned earlier that you have an opened end wrench that will fit, that will work, but I prefer a box end wrench.

 

The air intake is off of the car... Thanks to all for the advice. While the air intake is off, and after the routine servicing is done, is there a way to test if the auxiliary enrichment carburetor is causing the overflow? The only pancake temporary pancake air filter I could find is the K&N 56-1400. It may be all right temporarily. I left a message at Mann-Filter about an HD6 pancake but no response yet. What is the recommended pancake filter for my XK340 and where can I get two?

 

So long as the car is keeping twin SUs, the only criticism I have of the stock design(s) is that the air filter box blocks the view of a fantastic looking engine.

 

My '59 Bugeye had SU carbs as did my '66 Volvo 122-S (My wife's car). Unfortunately, my Lotus S4-SE had Zenith carbs. Anyway, I am a fan of SU carbs. Back to business, the rear carb intake has a wet stain that smells like old fuel about an eighth of an inch deep at the connection to the air intake. My current guess is the rear float needle valve is either sticking or gummed up. I haven't worked on the carbs so far because up until now the engine has been running well. The car has been on the road at least seven times, long enough to get above 70 degrees C before the last episode. Once before in the middle of those runs my wife mentioned smelling gasoline. I could smell it after she mentioned it but I couldn't see any leakage. As usual, I should have listened...

 

The air filters are available, Jaguar part number C19530.

You can start the car with the air filter off an observe the starting carb to see if there is a fuel leak.

 

Thanks for the tip about starting with the air cleaner off. I have a good fire extinguisher in the shop. The C19530 fits a Mark 1... My car is a 1967 Mark 2-340. I am going to search for a pancake air filter that fits the HD-6. I can't find a pair for Jaguar, but they must be available, perhaps for a big Healey, etc.

 

And S Type and Mark X. If you have the air cleaner housing that goes across the engine and is oval shape, that's the right element. If you have a round housing (like most Mark 2) then you need a round element, like most traditional American V8's have. I'm not sure if the 340 has the S Type style, or Mark 2 style housing.

 

Some 340's had ribbed cam covers & an S Type oval type aircleaner but with two trumpets sticking out of the inlet end & no convoluted pipe running to the front. Took same element as the S type.

Like this: (This might be a 240 but same)

 

There is only one way fuel is allowed into the carbs, and that's through the float bowl check valves, and they are the source of the problem.
Burlen sells new ones with the proper Viton tips, aftermarket were sold with some other stuff that swelled up and would not seal, so don't buy new old stock rebuild kits.
Grose Jets are even worse, they stick open and shut, either flooding or starving the engine of fuel, but mostly they stick open.

The factory settings for the jets are 7/16 _ you take a 7/16 round bar and set the "fall" of the float fork to that diameter, but there is a problem with that setting.
It comes very close to where it allows the fuel level to come just short of the jet bridge, also to the maximum level to the starting carburetor, so on a hot day, the fuel expands just enough to flow out of the starting carburetor and consequently past the jet bridge, this situation gets worse from the fumes in the tank pushing the fuel on the float valves.
That's why I opened up my vent in the fuel tank.

The solution to that is to open up the float fork more then 7/16th, it doesn't take much _ a couple of mm, you could probably go even a bit more.
The car will still have plenty of fuel as the atmosphere flows into the engine and easily picks it up when air flows over the jet bridge.
There is negative atmospheric pressure at the jet bridge, it won't matter if the level of fuel is a few mm below the factory setting.

By setting the float fork at a couple of mm more then it has to be , this lowers the level of fuel in the float chambers and lowers the level that reaches the starting carburetor.

That should solve you problem Morgan, the fuel smell is coming from the starting carburetor, and if you have faulty float check valves, then replace those.
There is also a special grooved fibre washer to allow the float chambers to "vent", very often this washer is omitted or installed wrong.
This is found where the long nuts are that hold the float lids in place.

Know that the starting carburetor is not of the greatest design, and this is one of it's problems, percolating hot fuel, so even with this modification, it still may play up on some very hot days and from engine heat sink.

Do you have the Bakelite heat sinks installed on you carburetors, that helps a lot too ?

 

I don't think you are going to find any decent pancake filters. Would be happy to be proven wrong. Most pancakes are rubbish.

 

Great post JeffR1. It contains loads of good information. I have the SU shop manual from Burlen, but the float valves and seats from them are out of stock. The two pages from British SUperior are the instructions from the two carb rebuild kits from right after the car arrived last December. I found the grooved washer in the kit, and the tip of the float valve needle tip is a rubber material. So, if the float fork is set at 1/2 inch the fuel level in the carb and the starting carb will be 2 mm lower than the 7/16 recommended setting. The inside of the carb throats and the inside of the aluminum air intake casting indicate excess fuel from the rear carb. The top of the starting carb appears to be Bakelite, but I do not know about Bakelite heat sinks.

Thank you for taking the time to share your knowledge. Regards, Morgan

 

"Burlen sells new ones with the proper Viton tips"

I have found proper Viton tips to be crucial. You never suffer float chamber flooding with them. The inline strainers are pretty useless & let large particles through. There is also an Aussie company that does proper Viton tips that's name escapes me. They do very good SU kits. If I remember I will post. SU's don't like dirty fuel.

These things don't do a good job.

 

Buy a Uni Syn Model A to balance carbs: Can be picked up on Ebay for peanuts in the fuel injection era.






Buy this book: Available on Amazon & elsewhere. Paperback & not expensive.

 

I have also had good luck with the "rubber hose method" detailed in the manual of listening to the intensity of the hiss. I balanced the carbs by listening and then put the flow meter on and the carbs were sucking equally.

The important thing with the hose to do it exactly the same on each carb, and make sure the hose is positioned identically in relation to the bore on each carb. Repeatability between each carb is more important than the exact technique.

 

Yes ~ Some people get it right & some don't. I balance multiple twin side draught Webers at variable revs through the range by pulling a plug lead on each bank fed & get it spot on by equal rev drop. It's a matter of experience.

Uni Syns are so cheap these days one gets lazy & and least has the assurance that it's right. SU's stay in tune for a very long while once correct unlike Italian engines with Webers or Dellortos.

 

I think the Aussie brand of SU float needle and seat that Glyn refers to may be the

FUELMISER SU-750NS Carburettor Needle & Seat

They definitely have a viton tip on the needle. Typically retail between A$25 and A$40 depending where you buy them.
Cheers

 

That's it Bill. Slipped my mind. There is also another company that sells all the respective complete SU rebuild kits. Main jet diaphragms are blue.

 

I appreciate that there have been starting problems and no signs of liquid fuel, which suggest a problem inside the carbs. However, it's still worth doing the easy things first and checking the banjo connections in the fuel line, one on each float chamber and one on each side of the filter. My car had a leak from one of them. There was no evidence of liquid fuel until I looked very close and the smell was more evident to the sensitive female nose than to mine. I think that there's also a coupling and a tee between the filter and the carbs.

 

Top plumbing from filter to float bowls.





Under carb plumbing. Held together with short rubber hoses & clamps. Not shown here & not mine. Long plastic drain tubes hang down from plenum drain nipples to prevent under-bonnet fires & dump gas onto the road. Same applies to float chamber drains but in metal pipes clamped together on oil filter bolt.

 

I have a set of these, almost to precise for what is needed though, but they do work well.

SU HS4, H6, HD6, HS6, HIF4, Hitachi Carburetor Synchronizing Kit | britishtoolworks