Photo request XK 140

I need to see the underside of an XK 140 intake manifold showing the connections between the Thermo carb and the intake manifold and especially where the anti-backfire valve is located,
If anyone can either refer me to such an image or ideally if you have that assy out of the vehicle could shoot a pic, it would be appreciated immensely.


Mike Moore

This is an XK140 manifold and carbs.
The anti-backfire valve should be in the flange that attaches under the manifold.

It looks like you have HD6 carbs rather than the original H6, and a horizontal starting carb inlet, so I don’t think yours will fit to this pipe.


Not sure about the 140, but on the 120 the tube (Starting Pipe) curves from the base of the starting carb. under the inlet manifold and goes to a flange secured by 4 bolts to the manifold. The starting tube goes into that flange and is secured by a large banjo-type union. That is where the anti-backfire valve is located. If you have access to a 120 workshop manual there is a photo of an early 120 carb. set up in which you can see the tube, Section C page C.9. Hope this helps.


Ron, thanks so much.I have been told several things about the carbs , including from Joe Curto, and they all seem to differ as to what they are. This car seems to be a real hybrid, The original engine is sittingoin the garage, the cam cover on the car says its a C (unlikely), the car has been converted from hydramatic-so the underside arrangement of clutch etc is different also.
I’m just thankful that I know the carbs USED to work, and they have been cleaned, properly kitted and I think with the help of you and others on this forum, I’m on the road to resolving the whole choke problem. It looks like if I remove those two nuts, I can remove the entire tun assembly. Is the anti0back fire valve inside the end piece? Thanks so much, Mike,

Chris,my arrangement is different to this one.The tube to the intake manifold exits horizontally and out the back the therm0 carb, Also, ion my carbs, I think my idle speed is adjusted by an air bypass screw as opposed to an adjustment of the throttle plates directly,

Thanks so much! Mike

Michael, I think you have the intake manifold and carbs from an XK150. Here’s a photo of the XK150 intake manifold and starting pipe arrangement. Unlike the XK120 and XK140 where a single starting pipe connects to the intake manifold, your thermo carb branches horizontally into two starting pipes. Then each starting pipe connects to the intake manifold in three places. I don’t believe an anti-blowback valve was used with the XK150 starting pipe arrangement. So there shouldn’t be a need to disassemble the starting pipes in order to clean a sticky anti-blow back valve.

(photo from Original Jaguar XK, Philip Porter, 2012)

Michael, I think you have the intake manifold and carbs from an XK150. Here’s a photo of the XK150 intake manifold and starting pipe arrangement.

Mike, I agree and appreciate this photo. Last last night I learned more about the variations of intake manifolds on the 150. I had felt the smaller tubes with my hands and could not imagine what it was. I am wondering if those tubes get plugged up with gunk? Is it worth trying to remove and clean it? How tough is it in-situ? I also read an extended discussion about the necessity of having anti-backfire valves in the 140, I understand this set up does not have the ABV, probably because of the several smaller tubes presenting less of a hazard, BUT I have had two fires already starting with a backfire of this engine. That makes me think the tubes may be plugged up and allowing gasoline to pile p n the tube-yet a backfire is pressure coming FROM the engine and if the tubes were plugged, it couldn’t start a fire. On theother hand, the owner says that all the years they had the car, it was hard to start and had to warm up for several minutes before it could move. I would appreciate your thoughts on the necessity to clean those smaller tubes.
Thanks, Mike Moore

Mike, here’s another photo of the starting pipes used on the XK150. I measured the inside diameter of the individual pipes as follows:

  1. The six pipes leading to the intake manifold - .18" diameter.
  2. The two pipes leading to the three-way coupler - .30".
  3. The single pipe leading to the thermo carb - .41".

My guess is the starting pipes are not plugged, but that the thermo carb is somehow at fault. There’s a brass disc that opens and closes the thermo carb to the starting pipes. I’ve seen cases where the brass disc doesn’t completely seal when the thermo carb shuts off. The brass disc is on a plunger rod that slips into the solenoid. Try taking the solenoid apart and polish the brass disc on some very fine sandpaper such as 1500 grit. Also make sure the plunger rod moves freely. This will help assure the thermo carb is not feeding the intake manifold after the engine warms up. Otherwise, there are a few adjustments to the thermo carb outlined in the Service Manual. Good luck!

This setup with the individual tubing is what I have seen on 3.8 liter engines. The 3.4 liter engines have a single tube to bottom of intake manifold. No anti backfire valve on my 3.4 liter xk150.

Thanks Kris!
Mike Moore