i have 84 xjs. and am running xm2 cams, euro downpipes and 5 speed
with 3.31 gears. seamed sluggish of the line so I advanced a
couple degrees. WOW what a difference. breaks tires loose when you
grab second. and pulls really strong threwout rpm. recently read
post about advancing to far and dont want to do that. where should
it be and how do I verify that its right? I run 93 or 94 octain gas
in usa–
john rinaman
zelienople,pa, United States
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In reply to a message from jrinam sent Wed 3 Jan 2007:
Hi
I have also tried advancing the timing on the XJ-S HE’s V12
distributor, by turning the distributor body (thus setting the
static advance), because mine also SEEMED sluggish to start OFF
with. It did make a big difference - there was power THROUGHOUT the
entire normal rpm range. Even the idle speed went up and had to be
readjusted via the AAV (auxiliary air valve).
I have advanced mine to just before the onset of pinking. Carry a
spanner and screwdriver with you and go for a drive. Adjust the
timing and drive, listening out for pinking. When you get pinking
you have gone TOO far. Back off the advance a degree or two, then
try again. You will hence find the optimum advance by trial and
error. DON’T run the car with persistent pinking as you will wreck
the pistons.
That optimum may only apply for that tankful of whatever OCTANE gas
you bought. You may like to carry that same set of spanner and
screwdriver to re-adjust the timing if the pinking resumes with
different tankfuls of petrol. Fuel in the USA can have different
ratings to those in the UK.
In reply to a message from teddykan sent Wed 3 Jan 2007:
thanks for advice. I had to remove cap to get to 3 allen bolts. is
this the only way? would be nice to adjust when running.–
john rinaman
zelienople,pa, United States
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In reply to a message from teddykan sent Wed 3 Jan 2007:
No matter what I do with the timing, my car still remains the same
color.–
The original message included these comments:
I have advanced mine to just before the onset of pinking. Carry a
spanner and screwdriver with you and go for a drive. Adjust the
timing and drive, listening out for pinking. When you get pinking
you have gone TOO far. Back off the advance a degree or two, then
try again. You will hence find the optimum advance by trial and
error. DON’T run the car with persistent pinking as you will wreck
the pistons.
There is an adjuster at the forward side of the distributor (perhaps
hidden by the cruise bellows). This has a locking nut, screw head to be
turned to advance/retard, and an advance scale. The distributor is made
in such a way that the base is held firmly to the valley cover by the
three allen-head capscrews, but the upper section is attached to the
base by 3 screws with springs beneath their heads, allowing the upper
section to rotate approximately 20 degrees.
If you are going to advance the ignition timing more than the factory
spec (18 degrees BTDC @ 3,000 RPM), I would suggest knowing exactly how
much additional advance you are adding, and increase the fuel octane 1
octane for each 1.5 degree additional advance, and ONLY doing this if
you KNOW that your distributor advance mechanisms are working properly
(which requires removal & disassembly, at which time you will
understand how to set advance without removing the cap ;-). Even then
you are putting your engine at risk of piston damage due to other
variants such as high air temperature, engine coolant temperature,
carbon buildup within the engine, etc.
Roger Bywater made two comprehensive posts on this subject
approximately November 1, 2005, which should be accessed from the
archives.
George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: jrinaman@zoominternet.net
thanks for advice. I had to remove cap to get to 3 allen bolts. is
this the only way? would be nice to adjust when running.
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In reply to a message from jrinam sent Wed 3 Jan 2007:
gbalthropxjs gave the correct advice. What he suggested, in terms
of changing the timing, is what I did to mine.
Do not tamper with the 3 allen bolts on the bottom of the
distributor body shell yet. Even when you can get some 10deg of
advance from them, don’t resort to that until the adjustment via
the eccentric screw on the outside of the dizzy is used up (this is
at the front facing forward, which has a neighbouring scale
markings).
And as gbalthropxjs has also advised, your centrifugal ignition
advance mechanism inside the unit can do with an overhaul. If you
rotate the rotor arm, you should feel some spring pressure trying
to return it back to rest. When you let go it should spring back
with a clunk (ie should be quite loose). If not then it’s time for
an overhaul and clean-up. There’s no point advancing the dizzy
without getting the centrifugal weights moving freely as well.
You can’t do this whilst driving, not like some vintage cars. With
the engine off load even revving it wouldn’t be much use. To test
the advance properly you need to put the engine under load (ie,
driving it, and rev up to 3000rpm).
Try this procedure and let us know how you got on.
Actually George I made those postings on the 18th and 20th
of December, but thanks anyway.
Anyone advancing the igniton timing beyond standard settings
should acquaint themselves of the risks involved.–
The original message included these comments:
Roger Bywater made two comprehensive posts on this subject
approximately November 1, 2005, which should be accessed from the
archives.
In reply to a message from RogerBywater sent Wed 3 Jan 2007:
roger, read those posts and that is why I am so concerned. all my
other vehicles are set with timing light and adjusted slightly for
performance. all are of lower compresion. my xjs had a flat spot
just off idle and was sluggish below 3000 rpm. I moved 2-4 degrees
and the difference is amazing. did not use a light nor know where
to set. I ALWAYS run 93 or 94 octain, calls for 89. so figured I
was safe for a couplr degrees but dont know if it was ever right to
start with. I want the best performance without melting pistons.
would this be 18? did develope new problem since advancing, when
stopped at light, idle will oscilate 3 or 4 times and then return
to smooth idle, whitch is now at 1350rpm, was 900 before timing
change. see no obviuos vacume leaks and wont reset idle til timing
issue is resolved.–
john rinaman
zelienople,pa, United States
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In reply to a message from jrinam sent Thu 4 Jan 2007:
The idle does rise with ignition advance because the combustion is
happening more efficiently. Do listen out for pinking carefully as
Roger Bywater points out this can be very destructive. Feint
pinking is not OBVIOUS but try to listen for it.
How did you set the ignition advance if you didn’t know where to
set??
Once you’re happy with the advance, go to the AAV screw (~13mm
across flats hex screw head on housing below left bank butterfly
throttle linkage on air filter housing). Turn it TILL the idle is
down to about 750rpm. This might cure the idle WHICH doesn’t then
OSCILLATE.
You could try the correct OCTANE fuel (about 95 in the UK?)
In reply to a message from teddykan sent Thu 4 Jan 2007:
us octain ratings different. 94 is best your going to get unless
using racing fuel. I set timing by ear, will set with light now
that I know where factory setting is. and then set idle. thanks.–
john rinaman
zelienople,pa, United States
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