Thanks Kris,
Your answer points out that I am so far from stock that all I really need is something that works. The Otter switch on this car was bypassed andAED was wired through a switch under the dash (where no one can see it! ) I get 12v when the sw is in one position, nothing in the other so the way this guy works, I just have to permanently ground one pole and power up the other, Part of my thinking is that I lost the wire which is supposed to be ground and I want the terminal on the AED end, It has to still be connected and is probably dangling someplace down there, Thanks for your help Mike
I think several people add a manual switch for the choke. That switch would be best if just made to be a supplemental ground. Sounds like you are on the right track. The aed makes a pretty loud click when it gets energized and a loud hiss when running energized. So you know if it is working or not.
Ha! I wondered why people calll it the “hisser”.
v/r Mike
Kris, as I think about it, it should be a switch to ground, It takes 12v from the coil, but as I think about it, when I was trying to figure out the wiring, when the switch was ON I was getting 12v at the end of the wire which went to the dash, That makes no sense if I already have 12v from the coil primary.
Mike Moore
Yes, this is one of the two ways to bypass the Otter switch, and some argue that it is the safer of the two by shutting off power to the non-grounded wire; the other being to run a wire from the coil SW side to the AED solenoid (AKA starting carb, hisser, choke) and put a manual switch on the wire to the grounding side of the solenoid.
I mentioned this in my Aug 30 response.
Yes, I remember that and have it printed out, At the time I thought “Well, I have THAT!” but I just realized yesterday (?) that I am switching a 12v supply to the AED terminal from the dash switch (I measured it at the end od the wire) which is already attached to the coil 12v supply and simultaneously grounding the AED with a separate wire. What I’m saying makes no sense, but next Friday I will check it out and make sure I am grounding the AED from the secret under dash switch and not supplying 12 v to it,.
v/r Mike Moore
Makes me wish I could be there with you to figure this thing out.
Possibly the PO’s wiring was all wrong.
I looked back through the thread and I don’t think you ever said if the car is still positive ground, or has been converted to negative ground, so I’ll assume still positive ground.
You should have one side of the solenoid negative (my white) from the coil SW or negative, and one side positive (my black) from ground (which was originally from the Otter switch). You can have your manual switch on either one.
Here’s another tip for when you get it running. If you are running and switch off the AED solenoid, and then change your mind and switch it on again, the manifold vacuum will hold the swivel valve closed, and you won’t have the AED, until you hit the gas pedal, then it will open.
BTW there is supposed to be a fiber gasket under the solenoid body, although it will run without it.
Thanks Rob-The gasket sounds like it might l be a problem , The solenoid cap (plastic) was broken inlets o pieces, We bought a new one and it is difficult to get on, I do not know if there is a fibre gasket, but if not, it will add to the high of the star making the car even tougher to get on-just another challenge! I seriously appreciate your help,
v/r, Mike Moore
Oh yes the car is pos ground. The owner Andy Leavitt somehow drove it for years with a loose battery in the starboard battery compartment held in only by the two battery cables and the access panel! I should have bought the entire battery box but instead I bought a single 12 v battery hold down and fastened it to the replacement florae had fabricated and installed of aluminum plate.
interesting on this start carb topic: see Service Bulletin 112, p 2, about troubles with the thermo sw (should cut out approx 35C) there is a modified switch available and recommended: C2474 identified by a green spot on the front cover. SB also.discusses the color of the impact washer at the far end of the central tube. Dark red is what it should be. An improved machined plunger is part no 3205. IF the washer is dark green or cork, with " great care" . (the SB describes the care, and “how” and use of special tool called “pencil” )…remove and replace with a red fibre washer,part 3133/1 and new plunger part 3205.
Nick
Hi Guys, new to the group but have found your forums useful as I’ve been going through a customer’s 1955 xk140. I’ll dive right in to see if anyone can lend some ideas on fine-tuning the starting carb. The engine is healthy, compression is good. timing has been set as per the manual. all new tune-up items, as well as freshly, rebuild carbs by a reputable source here in the USA. (Joe Curto cabs in new jersey).
Upon installation of the carbs, I ran through my typical “lean best” method for adjusting the mixture, plus balanced each carb individually before attaching and adjusting the linkages. Idle sets very nicely at 750ish rpm. The otter switch is new and works well…shuts off at 135f. The car runs great and pulls as it should throughout the RPM range.
My issue is with the tuning of the Starting carb. I have gone through the procedure detailed here on the forum and brought the engine to operating temp, then set the “stop nut” on the starting carb. by shorting the otter at this temp I get a very nice rise in RPM (200) and a good strong hiss, all indicating that the starting carb is working as it should.
Next starting it up cold, the otter engages and the starting carb hisses, but no increase in RPM. I have raised the throttle via the linkage as instructed to get the starting carb to “grab” and it will hold the needle in the down position for a few seconds but slowly lose its “vacuum” and the needle raises…which makes the starting circuit nonfunctional, RPMs drop and the engine will die.
That’s where I’m stuck. I can continue to blip the throttle and limp it along but I’m hopeful this carb should act as a choke on other systems and hold the RPM high until the otter tells it otherwise. I can raise the base idle but that’s a bandaid that then gives me an undesirable high idle once warm.
Any input would be appreciated, let me know what details I’ve missed.
Thanks, John.
Hi John,
Wellcome!
My first bet is that you do not have the AED set rich enough. This website has a graph showing how to ensure it is rich enough: The SU Starting Carburetter.
I would start off by adjusting the mixture nut to see if it cures the problem.
Regards,
Clive
Thanks, Clive this is one of the videos I’ve referenced. I’ll go richer and see. I can always go back 
John
Is there information available to identify the various SU carbs used on the XK140MC?
There is the Spare Parts Catalogue, H6 and H8 types.
H6 has a throat measuring about 1-3/4" and the H8 throat measures about 2".
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Thanks for the information. I have the C head. Maybe the special H8 carbs. I could send a photo if you would verify.