Early Jaguar Auto Enrichment Device

I have an odd problem on my 1965 Jaguar S type with its auto enrichment
device. It starts (just) but idles/runs poorly until warmed up.

The system is twin SU carbs and a simple third 'carb' that is solenoid
operated and quite simply dumps additional fuel into the manifold. The
solenoid actuates at below 30 deg and is very obvious in its operation
(loud hissing) as a plunger lifts a 1/2" brass disc off a metered orifice
allowing air and fuel to pass through to the manifold.

The solenoid operates and the plunger moves freely on and off the car
with a nice hefty click but fitted with the engine running (I just short
the solenoid to earth, bypassing the temp switch) it can't lift the disc
off the orifice due to the vacuum at idle and the click is decidedly
feeble and no hissing.

There is a 1v voltage drop due to the aged wiring loom but it doesn't
matter if I hook up a direct feed from the battery - it still doesn't
have the strength to lift the disc.

It's the original one, so do solenoids go 'off' with age?

Anyone have an idea of the resistance I should expect across the
terminals?

Or is it something else?

 

How did you get it to make a nice hefty click off the car? And they don't
normally go soft, but you may need to move it slightly closer to get
enough initial pull in.

 

They're very simple devices - see here for diagram:
http://www.sweller.co.uk/docs/jag38saed.pdf

I took the solenoid part off the enrichment assembly and supplied it with
12v - the iron plunger/spring/disc retracted quickly and with a nice
hefty click.

The winding part of the solenoid can only be in one position so there's
no adjustment in relation to the plunger.

 

I've already stripped it - the disc is still firmly attached to the
plunger mechanism.

Looking mojo-ish...

 

What is the solenoid resistance?

 

Don't know - forgot to check it. What should I expect?

 

At a guess, about 4-10 Ohms, but that's a guess. If it makes a loud clunk
when off the car then I'd still bet on either the contacts to the solenoid
being crap or the live feed.

 

Hmm I'm wondering if the whole solenoid mechanism should be airtight -
that way it wouldn't matter how low the pressure was on one side of the
disc, it should have equal pressure on both sides iyswim? Does the coil
etc. have a perished rubber seal perhaps?

 

It makes a loud clunk when it's on the car too - just not when the
engine's running.

I'll stick a meter on it tomorrow.

 

Failure of the insulation between layers of the coil can make the
solenoid much weaker.

 

Indeed, as can failure of the varnish between the layers of a laminated
core, although car stuff isn't always that sophisticated.

Chris

 

Solenoids are generally air cored and have few layers.

 

Yep, certainly in car-type sizes; I've mostly dealt with ones several
orders of magnitude larger in industrial situations, so very different.

I was really just agreeing with your statement that a solenoid can fail
in a way that allows it to operate, but weakly.

Chris

 

Yes, they do. Especially ones of that era.

 

Duncan Wood submitted this idea :

At the back of my memory, I seem to recall they used to fit a manual
switch to power the solenoid, bypassing the thermal switch.

 

steve auvache used his keyboard to write :

I also wonder if something might have become magnetised, which could be
countering the solenoids action?

 

It'd have to be very magnetised I note that Bentley still sell the
original service manual , which probably answers the question of what it's
resistance should be.

 

I have the factory manuals for the XJ6, and early cars appear to have the
same unit. No resistance given.

 

I had bad starting problem and running until warm on a 2 year old XJ6 I
had while working in Southern Germany.

I constantly looked like the third starting carb.
Tried lots of things over some time but could not get 'good starting and
running'. I even put a new unit on.
I ended up taking the third carb off and blanking the hole.

The car would then start no problem in minus 10 deg by fanning the
throttle when starting it. Once it started it needed just a little help
fanning the throttle for the first minute to pull away.
I never bothered to put it back on. It made not difference in normal
temperatures.

 

Bad form following your own posts etc.

I've just thought. I didn't take the starter carb off. The final fix was
the fuel line blanked off. Cab in place with the electrics disconnected.

It was like that when I PXed it for the next car.
(1979?)