[v12-engine] XJ12 running very rough ideas please

V12-Engine
1

Ok, so I sterted my XJ12, on Strombergs today after being stored
for 6 months. It was running fine when it went away, and now its
proving very difficult to start. Did a 12 mile run in it and
basically, if you keep the revs up it will drive, but if you let
the revs drop it will stop and take a lot of work to get going
again. Its on 12 intermitendly and most of the time its coughing
and backfiring. All the plugs seem to be burning ok, after the run
I checked that. There are no obvious signs of vacumm leaks. Could
it be ignition, it was a brand new amplifier last year. I have a
photo shoot for a magazine tommorrow hence I need to sort it first
thing tomorrow if I can. If the diaprhams were preished could this
be the problem. They were new about 5 years ago. So
frustrating!! please help. Oh, and when it first started up it
seemed fine although the battery had been down it ran pretty well
on fast idle for about 10 minutes, now all these problems. It
will, as is always the case, but something simple, but
WHAT???–
old wrek
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2

Was the gas tank full when you stored the car or did you add some stabilizer
to it? It sounds like old gas that’s picked up some water from the long
storage period.

Daniel
1994 XJ12
1995 XJS 4.0-----Original Message-----
From: owner-v12-engine@jag-lovers.org
[mailto:owner-v12-engine@jag-lovers.org] On Behalf Of old wrek
Sent: Wednesday, March 09, 2011 10:45 AM
To: v12-engine@jag-lovers.org
Subject: [v12-engine] XJ12 running very rough ideas please

Ok, so I sterted my XJ12, on Strombergs today after being stored
for 6 months. It was running fine when it went away, and now its
proving very difficult to start. now all these problems. It
will, as is always the case, but something simple, but
WHAT???

old wrek

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3

In reply to a message from Daniel Arsenault sent Wed 9 Mar 2011:

Maybe, I have added fresh fuel to both tanks, but they were both
low before. I know modern fuels can go off but I would have
thought it may have been diluted by the new fuel?–
old wrek
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4

In reply to a message from old wrek sent Wed 9 Mar 2011:

It may take a while for the new fuel to dissolve the deposits of
goop that have formed. Take the fuel hose off the downstream side
of the pressure regulator to see if you get good flow. Then take it
apart to clean the bore, ball and spring. Might be a good time to
change the fuel filtre in the spare tire compartment as well. While
the tools are out and the hood is up, check the diaphrams, that the
pistons move freely, the choke does in fact shut off completely and
the oil levels are even and correct. I’m assuming (yes) no vacuum
leaks. As a high-tech digital last resort, find a hammer and lightly
tap the things while the fuel pump is running. Nice car. Let us
know how it goes.–
The original message included these comments:

Maybe, I have added fresh fuel to both tanks, but they were both
low before. I know modern fuels can go off but I would have
thought it may have been diluted by the new fuel?

–
Don 74 SII XJ12L
Port Colborne, Ontario, Canada
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5

In reply to a message from Donald Fox sent Thu 10 Mar 2011:

Guys, thank you very much for the considered advice . The great
news is that it is now perfect. The bad news is that I was unable
to isolate exactly what it was, but I am pretty sure it was stale
petrol and carbs/lines/filters clogged up. I tapped the pumps,
which is a trick I learnt years ago, but they seem to be working
ok. When I tool the main carb fuel supply off the fuel that came
out was very dark, almost treacle, but its only been in there since
last October. Anyway, to complete the story. I got her running late
yesterday, and took for what you may call a bit of a thrash, or in
American parlance, took it to the wood shed. Still missing like a
pig, and gave up on it until today. Went down to the car first
thing, started it up…perfect. Took it to the fuel station,
filled both tanks ( took out a mortgage first) and its has not
missed a beat all day. I have to conclude this is yet another
story of rubbish modern fuels killing our beloved cars. Maybe,
just maybe there was some damp in the ignition, and the heat soak
after I drove it hard last night, dried it all out, but I cannot
ppin it down for sure. Anyway, once again, many thanks for helping
with advice, sometimes when you have a problem like this you need
to discuss it with others to make sure you are not missing
something obvious. Happy days, and I am off to buy some fuel
stabliliser for next winter!–
old wrek
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6

In reply to a message from old wrek sent Thu 10 Mar 2011:

Congratulations. You won over frustration.
Daniel Arsenault and Don Fox were surely right: bad ‘‘old’’ fuel.
Especially water in the fuel.

SU’s and Strombergs are very sensitive about water, as H20 just
doesn’t like to be pulled through the jets’ metering needles that
control petrol (gasoline) flow. Water doesn’t vaporize easily when
cool.
Once water-logged, the jets are VERY balky until cleared.

You gave the clue when you said after cleaning out old fuel
and ‘‘taking it to the woodshed’’ for a thrashing:
‘‘Still missing like a
pig, and gave up on it until today. Went down to the car first
thing, started it up…perfect.’’

After warming the engine the previous day or two, the excess water
evaporated off the jets. That’s my conclusion.

Of course, other types of carbs don’t like water either, or bad
fuel. I have started many an unused engine for friends by replacing
old fuel and blowing the jets clean. They just can’t believe
fuel ‘‘dies’’ from old age.–
XJS coupe 1986 V-12, California
Santa Cruz, California, United States
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7

Its weird though how storage issues can be finicky, I took the XJS out
today, first time it has been run in months. Let’s put it this way, the last
time I drove this car it was so long ago the clock didnt need to be changed
today, October at least. The car ran perfect on its six or eight month old
gas with no problems on 20 miles of in town driving up to 55mph. It was a
blast reminding myself how fun these cars can be and sad at the same time
that it doesn’t get the use it deserves.

I left the car with 3/4 tank of gas in a dry garage though and the dry Los
Angeles climate is not exactly conducive to putting water in the gas.
Outside storage would no doubt make for more problems as would an emptier
tank I guess.

Daniel
1994 XJ12
1995 XJS 4.0----- Original Message -----
From: “Wudpecker” wallacewood@sbcglobal.net
To: v12-engine@jag-lovers.org
Sent: Saturday, March 12, 2011 5:22 AM
Subject: RE: [v12-engine] XJ12 running very rough ideas please

In reply to a message from old wrek sent Thu 10 Mar 2011:

Congratulations. You won over frustration.
Daniel Arsenault and Don Fox were surely right: bad ‘‘old’’ fuel.
Especially water in the fuel.

Of course, other types of carbs don’t like water either, or bad
fuel. I have started many an unused engine for friends by replacing
old fuel and blowing the jets clean. They just can’t believe
fuel ‘‘dies’’ from old age.

–
XJS coupe 1986 V-12, California
Santa Cruz, California, United States

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8

In reply to a message from Daniel Arsenault sent Sun 13 Mar 2011:

Right, Daniel. A dry L.A. climate and storage with 3/4 tank of fuel
helps a lot.
There’s a reason California cars are preferred to say, Washington
(D.C. or state). Less humidity and no road salt.

When I was washing cars and trucks to pay my way through college at
UCLA, the head mechanic gave me puzzling advice when I bought my
first car (a used '47 Plymouth coupe for $100).
‘‘Always keep your gas tank full.’’
‘‘Why?’’ I asked him.
‘‘Keeps the rust out of your gas tank and water out of your carbs,’’
he told me. ‘‘An empty tank will condense water.’’

When we are talking old fuel, 1 year is not that old on 3/4 tank.
Three or more years is.
Since all my Jaguars were old when I got them, old and rusty fuel
was now and then a problem. One XK-120 roadster sat abandoned in
the woods for God knows how long–at least 20 years. I drained the
tank of brownish fuel, blew out the lines, but did not coat it. It
was fine.
You would be shocked to see the rust pits in the water-filled
cylinders (the head was gone). Even more shocked to see that I
didn’t bore the cylinders. When I saw they were 4-ring pistons, I
had them knurled and put them back after only honing the bores. My
theory was the rust pits would hold oil. They did. Didn’t use any
more oil than other 3.4 engines!
I did coat the tank of another XK-120 (a drophead). I wouldn’t do
it again unless the tank actually leaked, it was so much trouble.

Wish the later model Jags had those glass fuel filters you could
see into and clean out. Always knew if there was a fuel problem.

The little fuel reservoirs on the SU carbs also would act as
accidental filters and fill with crap, too. Worth checking.
But we’re not talking XK-120’s here, so I’ll stop if no
questions. :-)–
The original message included these comments:

I left the car with 3/4 tank of gas in a dry garage though and the dry Los
Angeles climate is not exactly conducive to putting water in the gas.

–
XJS coupe 1986 V-12, California
Santa Cruz, California, United States
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