After many years of collecting classic Cadillacs, I sold the old slush buckets and bought a rip-roaring xk120 in BRG that was restored beautifully in the 1990s. It arrived yesterday and ran well–I puttered her up the driveway and put her in the garage for the night.
Today she won’t idle. I can get her to start if I keep my foot on the throttle, but it dies the moment I release the accelerator. I hear the fuel pump clicking when the ignition is on. The carbs don’t seem to be leaking. There is a lot of smoke out the tailpipe
Congratulations on buying the most beautiful car ever, without which there might never have been a Corvette.
And welcome to the group.
My first thought is that you may not know about the starting carburetter, located between the main carbs. This is for cold starting instead of having a choke.
It is electrically operated by a black solenoid on the top, which is switched on automatically when the engine is cold by a thermal switch on the intake manifold, known as the Otter switch.
When this carb is switched on and the engine is idling, there is a distinct hissing noise, thus some people call it the hisser. And it will idle fast, until it warms up and the hisser closes. It should not need any foot on the pedal to start cold or even hot.
Some people including myself bypass the otter switch and run the carb manually by a toggle switch under the dashboard.
Yours may have this modification.
I would look under the dash for a hidden switch, and in any case determine if your starting carb clicks on when you switch on the ignition before starting. Have someone turn the key and you can feel it click once.
Ahah! @Rob_Reilly thank you very much! I will begin with the otter switch (fantastic name) and am grateful for your diagram/labeling. Not only is this forum Jag savvy, but it’s also tech savvy! Wow.
I think the little starting carb might be the culprit. I noticed that one of it’s wiring leads is new plastic and seems to have been replaced. All the other wiring on the car has the stock vintage-wire appearance. I hear no hissing, but of course that’s hard to hear over an engine held at 1,500 rpm to keep the old girl from croaking.
And yes, this is all very new from big old Cadillacs of this era. First of all, I was surprised that this car had an electric fuel pump and 12 volts. Add a starting carb and now I’m really impressed. (and yes, I think it’s the sexiest car ever built–certainly the best-looking car I’ve ever owned)
(and yes, I think it’s the sexiest car ever built-certainly the best-looking
car I’ve ever owned)
Hi Morgan,
I think you’ll fit in just fine with this group!
Because of the smoke from the exhaust, one other thing to investigate is a
sunk or stuck float, which would dump too much fuel into the engine. When
you turn on the key without starting the engine, the fuel pump should click
rapidly for a short while and then slow down to maybe one click per second
or less. If it clicks faster then check for fuel running out of an air
filter. Does one exhaust smoke more than the other, assuming duals? That
would give you a clue as to which carb was giving trouble.
Mike Eck
New Jersey, USA www.jaguarclock.com
'51 XK120 OTS, '62 3.8 MK2 MOD, '72 SIII E-Type 2+2
Coming through the giant haze of smoke, my neighbor kindly informed me through the smog that both tailpipes were smoking. Of course I could not see, having to hold my foot on the gas to keep her going.
The fuel pump is ticking. A few times upon turning the ignition and then once every 5 seconds or so.
The “new” wire from the starting carb leads backwards to under the dash. There is no additional switch that I can find (yet). I’m tempted to remove the lower fascia to investigate.
Hi Morgan,
If your problem is purely cold start up, you shouldn’t need to give it revs for too long.
If you consistently have to increase the throttle setting to keep the engine running there must be a secondary fault.
If the hisser is energized (via an alternate switch since the otter isn’t connected).
If a float is sunk, sinking, or not closing the float chamber needle valve.
If one or both of the float vent lines is plugged.
If one, or both of the carb pistons is sticking.
But it sounds like the hisser is being energized and that it is adjusted too rich.
One way to weaken the hisser when it’s doing it’s thing is to push down on it’s needle while the engine is running. If you can get the engine to idle without holding the throttles open, then the hisser just needs adjustment.
What colour is the smoke? I can’t imagine that an overfilling issue would create a ‘fog’ that your neighbour had to walk through. Over-fuelling would give a black discharge from the exhaust white smoke would be water related, and would be more inclined to be more ‘fog like’
Gents, you have been marvelous. The culprit was indeed the hisser. I disconnected that blue wire and heard a click when I did. Reconnecting it, heard a click once more. Starting the car without the hisser was a breeze and it runs beautifully.
Now I’m hooked though. This is the first I’ve driven a XK120 and I’m wondering why I took so long to buy one. My left knee bangs the door, my right knee cuts off the ignition, the asphalt is alarmingly close, the top of my head is over the windshield while the tops of my shoes hit the bottom of the dash. I LOVE THE WHOLE THING.
Thank you for all of your help. I’m going to trace that hisser wire to the switch must be hidden somewhere.
Hi Morgan,
The starting carb solenoid normally has two wires on it. One is the hot, connected to the ignition circuit. The other normally goes to the otter switch which connects it to ground when the switch is cold and powers the solenoid, which opens a valve in the starting carb. When the otter switch gets warm it goes to “open” thus disconnecting the solenoid from ground and the solenoid valve closes.
A toggle switch connecting to ground takes the place of the otter switch so you can shut off the starting carb valve whenever you want to.
Just a tip, if you do reconnect the hisser and it works, once the engine feels sufficiently warm to run without it you can turn it off by quickly turning the ignition off and on.
Your car looks like it has been restored to the highest level. How is it that the owner or dealer didn’t inform you about the starting carb switch? Also, where are you located?
Yes, it is beautifully restored but has been in the care of a trust for some time. As it turns out, an interim mechanic wired the hisser to… the cigar lighter!
I’d like to restore the hisser wiring to the otter. Does anyone know if there’s a solution/upgrade that can be hidden in the otter?
Easy to restore. From the engine bay picture you sent, it looks like your wiring is in great condition or a replacement and probably still there. There should be a white wire tucked away or taped off that comes from the negative terminal of the coil (marked SW) and goes to one side of the starting carb solenoid. You will then need to add a short black wire from the other side of the starting carb solenoid to the spade connector (you will need a female spade connector on the new wire) on the Otter switch. You have a later type otter switch with the spade. Originally they had a threaded terminal for a lug connector and had a nice chromed brass acorn nut on it. You should check to see if the Otter works first by checking continuity across it (spade to ground) with it cold (should have continuity) and hot (no continuity).
Most of us either eliminate the Otter and add a direct acting toggle switch or as in my case, add the switch in series with the Otter. When you are ready, we can help you with this (as Rob alluded to). The Otter keeps the car running too long in the enriched condition for most of our liking, especially if you start the car and leave it idling.
So, as far as you know, there is no switch, and the starting carb is wired to the cigarette lighter and stays on all the time? Would really think there is a switch there in series with this wire. Otherwise, it would run full rich and never cut out which would be un-driveable. Hard to imagine anyone would do that.
I spoke to the former mechanic and he told me the cigar lighter triggers the hisser. I’m not a fan of that setup. Although I’d never do anything so ghastly as to light a Romeo and Julietta Short Churchill with an electric lighter (unless under extreme circumstances), I would like a functioning cigar lighter if only for iPhone purposes.
Interesting. Sorta clever. So does this mean the Otter was NFG?
I like your choice of cigars.
But most likely your car is the original positive ground. Modern cars are negative ground. Some people have switched their cars to negative which is not too hard to do. You would need to do this or wire a separate receptacle from the battery like I have done for the iPhone.
First thing is to determine if your car is still positive ground, or has it been converted to negative ground.
Then is your coil marked SW and CB, or it is marked + and - on the side terminals.
The starting carb normally has a white wire going to the coil on the SW (switch) side or - minus side if it is positive ground. If it is negative ground the white wire would go to + positive on the coil.
The other wire on the starting carb may be white with black stripe or just black like mine.
It goes either to the Otter switch or to a toggle switch with the other terminal on the switch connected to ground.
Here is an original type Otter switch made by Otter Controls Ltd of Buxton Derbyshire.
When the Otter switch is cold it connects internally to ground. When it is hot it disconnects.
Hopefully you have or will soon get the Service Manual, which has the wiring diagram in it. This manual is often on ebay in paper or from parts vendors on CD-ROM.
Depending on how critical originality is to you, Fossway Performance make a replacement for the Otter switch that uses a modern sensor. I have used one on my Series 3 E Type and it works very well. On the E it’s used to switch the fans on and requires a relay but I think it would operate the starting carb. OK without one.
Please remember that the Otter switch for the Cold Starting Device is intended to switch off at 35 C.which is way below the switching temps of the E-type Fan switch. Cannot find the correct version at Fosseway.
Morgan,
I know many people have difficulty with switching off the Cold Starting Device at the right moment, but my (still original) Otter switches off between 30 and 60 seconds depending on the weather! I had to (carefully) open the switch and bend the bi-metal spring just a little bit. See photos below. After a few attempts I obtained the correct time which still works fine after 5 years.So if you’re not afraid…
