[xk-engine] D-Type ReCreation Engine - Webers - Question

Hello All:

Have a D-Type Recreation with a 4.2L XK on it. The car has
triple Webers. Have a couple of problems.

Car has decent torque, idles nicely. I think there is a
transition problem (common Weber problem as I understand
it). Also starves for fuel in higher RPM’s (air
correctors?).

Spec is as follows from the folks who built the car for us:
Engine is from an 85 Series 3 XJ6
Ported, polished, lightened, and balanced
Modified S3 fuel injected big-valve head
275 Rob Beere Cams
3x 45 DCOE Webers on Rob Beere Manifold
Lightened 3.8 flywheel
Competition clutch assembly
9:1 comp ratio
cast pistons

I need a baseline on what these things should be jetted
at…

all help is appreciated. If anyone knows of a mechanic in
Chicagoland who does Webers please let me know.

Best,
Royal Lichter–
'71 XKE S2
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In reply to a message from rlich8 sent Fri 27 Mar 2015:

If it runs as well as you describe you already have your
baseline. Anybody else’s jetting will be a crap shoot for
your specific engine as there are so many variables.
Buying six of everything gets very expensive doing it
trial and error so you need a full rolling road session.

Are the carbs Italian Bologna Webers or Spanish, or Asian
copies or what?

Is your car a Realm Engineering-based D?–
1E75339 66 D, 1R27190 70 FHC, 79 S2 XJ12L
Gaithersburg, Maryland, United States
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In reply to a message from rlich8 sent Fri 27 Mar 2015:

Never mind the transition, do some plug readings if you think
you are leaning out at top end, increasing main jet alone will
not help, if your plugs are white you need a guide on emulsion
tubes and air correctors, if you have 38mm auxiliary
venturies, try dropping to 36 for road work, the difference
will amaze you, instant tractability at low rpm, if you have
spent money with Rob Beere, he should be able to give you an
approximate formula, but the rolling road and a jar of jets is
what will eventually do the trick�also look for different
readings between linked throttle valves, the shafts can be
lightly torques in opposite directions to correct any
significant imbalance…–
The original message included these comments:

Hello All:
Have a D-Type Recreation with a 4.2L XK on it. The car has
triple Webers. Have a couple of problems.
Car has decent torque, idles nicely. I think there is a
transition problem (common Weber problem as I understand
it). Also starves for fuel in higher RPM’s (air
correctors?).
Spec is as follows from the folks who built the car for us:
Engine is from an 85 Series 3 XJ6
Ported, polished, lightened, and balanced
Modified S3 fuel injected big-valve head


Keith.P. Series2 Roadster
exmouth, United Kingdom
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In reply to a message from sozfingers sent Sat 28 Mar 2015:

Consider including electrical measurements in your baseline
information. Ignition advance charts for all engine load and
rpm ranges used are worth measuring when pondering air/fuel
matters. It is pretty common for ignition advance in hobby cars
to be good at static and idle and then vary from desired
advance as the rpm and load moves away from the easily measured
conditions. Total advance from mechanical and vacuum devices
may not be what is assumed. Also, use of modern ‘‘pointless’’
ignition modules can be pointless if the correct advance curve
is not verified. How many people have found switching from
points to electronic ignition led to high rpm stumbling which
may have been interpreted as too lean?

Another thought on the carb side is to use wideband air/fuel
sensor to help guide the carb settings. This modern tool has
value, a sensing technology used on large numbers of new cars.
The old school methods can work gratifyingly, superbly well in
experienced hands, they leave more uncertainty in non-
specialist minds. Multiple ways of measuring gives more
confidence.–
Roger McWilliams
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In reply to a message from rlich8 sent Fri 27 Mar 2015:

Guys,

Thanks for your posts. To answer some questions.

These carburetors are of the Spanish variant. My car was
built by Classic Jaguar Replicas in the UK. They were
unfamiliar with the setup of Webers.

With respect to ignition: I’ve had the distributor set up
with Jeff Schlemmer at Advanced Distributor. It is an old
fashioned Lucas points distributor with a copper lead cap
and a stud-less rotor. I’m personally not a fan of
contactless/electronic systems. I run good old fashioned
points on both of my Jags. Don’t quote me, but I believe
Jeff sets up his dizzies for approximately 36 degrees all
in. Our car isn’t running vac advance; totally pointless
for a car that’s meant to be driven fast.

‘‘How to Power Tune The XK Engine’’ suggests 36mm or 38mm
chokes. I know I am not running 36mm.

If I have to, I can set up a laptop with a wideband O2, but
I have a feeling I’m so close because the car actually makes
good power… like I said the only issues I’m having is
slight transition issue and hesitation in the higher RPM’s.

Thanks guys, I’ll continue to post as this processes.–
'71 XKE S2
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In reply to a message from rlich8 sent Sat 28 Mar 2015:

Good details to know on your distributor. Jeff Schlemmer has done
good work for me also. When a distributor is worked on, the repair
shop must make some estimate of spring rate, and so on. Jeff will
set up for his best estimate, I can tell you that measuring the
distributor advance curve in final installation to compare final
result with specific curve of interest can lead to further changes
even for a good rebuild. And unless the repair shop had the exact
curve to match, their estimate may still deserve some further
twiddling. Sometimes an intended 36 degree advance turns out to be
a bit more at high rpm and the engine does not fully appreciate
its resources then.–
Roger McWilliams
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In reply to a message from rlich8 sent Fri 27 Mar 2015:

Royal,

One trick to work out when the transition is occurring is to
remove the emulsion tubes so that the main circuit doesn’t
work. You can road drive it but realize it will die when you
hit the main circuit. Checking it on the back streets in
first should keep you a bit over the speed limit. That will
give the you the rpm when it is going to the main circuit.
probably in the 2500 to 3000 rpm range.

When you say starving for fuel do you mean it misses? At
steady acceleration but if you boot it so the pump jets kick
in it is OK? I has a similar issue and you could see it
going lean using colortunes.

Check the idle jets - I think I am running 65 F8’s - was
running 65 F9’s I think - went bigger anyway.
Don’t have the spec sheet with me but will check and let you
know.
idle jets 65 F8’s
Main Fuel 140 I think
Main Air 195
Aux chokes 38

If they are 45DCOE 152’s then idle mixture screw should be
about 2 and a bit turns off the base (within the ‘‘usual’’ 2 to
2.25 to 3 turns out… I have a fourth progression hole that
sits over the butterfly. Pretty stock mod to the 152 models.
The pre 152’s have a much coarser idle mixture screw thread
and adjustment is I think around 1 turn of the bottom.

If the carbs were set up on the engine then the jetting
should be close. I made the change to the richer jet after
10% ethanol became the norm.

Regards

Keith–
The original message included these comments:

Car has decent torque, idles nicely. I think there is a
transition problem (common Weber problem as I understand
it). Also starves for fuel in higher RPM’s (air
correctors?).
I need a baseline on what these things should be jetted
at…


Keith Bertenshaw
Rockaway, NJ, United States
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In reply to a message from KeithB sent Sat 28 Mar 2015:

Correction

Main chokes are 38mm and aux chokes are 4.5.
Main fuel is 160 and F2 emulsion tubes.

I have run 36 and 38 chokes and not really noticed the
difference in torque - possible because the engine is very
torquey anyway.

My engine is similar 9.4 compression but with a Rob Beere full
race cam and with the exception of the idle jets was his setup.

WRT timing, I run a Mallory Unilite - swapped out the Lucas.
Interestingly the ‘‘books’’ all recommend advance in the 38
range. I am running 30 all in around 2000 rpm with timing at
idle around 7. As opposed to the stock 10 I think?

But I don’t think your issue is electrical…

Regards

Keith–
The original message included these comments:

Main Fuel 140 I think
Aux chokes 38


Keith Bertenshaw
Rockaway, NJ, United States
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In reply to a message from rlich8 sent Sat 28 Mar 2015:

Are you running it with air filters or otherwise ??–
The original message included these comments:

In reply to a message from rlich8 sent Fri 27 Mar 2015:
Guys,
Thanks for your posts. To answer some questions.
These carburetors are of the Spanish variant. My car was
built by Classic Jaguar Replicas in the UK. They were
unfamiliar with the setup of Webers.


Keith.P. Series2 Roadster
exmouth, United Kingdom
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In reply to a message from rlich8 sent Sat 28 Mar 2015:

I think the Spanish and Asian carbs have three progression
holes compared to five on full Bologna carbs. So
transition is known to be worse but you should still
eventually be able to dial it out.–
1E75339 66 D, 1R27190 70 FHC, 79 S2 XJ12L
Gaithersburg, Maryland, United States
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In reply to a message from PeterCrespin sent Sat 28 Mar 2015:

Hi Pete,

The 152’s have three progression holes, (there is a 152G
with 4) and the problem being that the ‘‘ideal’’ according
to Weber is that the butterfly covers the first
progression hole at idle. To get the butterfly in that
position on my engine that was at about 1900 rpm! So that
meant up to that point the idle jet was the sole source
of fuel. The progression holes are not so much at
transition but off idle with off idle stumble, And yes
you can dial it out by larger idle jets but that ends up
very rich - in the 10 AFR range and fuel economy goes out
the window. (and possibly the oil off the cylinder
walls).As the main circuit isn’t kicking in until around
3000 rpm in my case you were/are mostly always on the
idle circuit. I went from mpg in the low teens in mpg to
the high teens and close to 20 on a good day. Sort of
important to know the range without a fuel gauge…
In short it is where the progression holes are and how
big. The ‘‘spec’’ is 18mm of the carb mount face and offset
1.5mm I think. And the hole is 0.5mm. Old article in E-
Type that I found a few years ago…
I think with 10% EtOH the first hole could be a little
bigger but close enough.
Given that the progression holes - placement and size -
were part of the Weber design for an engine this is an
important part. Again however, not a lot or any
documentation that I know of for the progression hole
specs for each of the different models of Weber carb and
engine. Sure some of the tuners have them from experience
but’‘proprietary’’.

Regards

Keith–
The original message included these comments:

I think the Spanish and Asian carbs have three progression
holes compared to five on full Bologna carbs. So
transition is known to be worse but you should still
eventually be able to dial it out.


Keith Bertenshaw
Rockaway, NJ, United States
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In reply to a message from rlich8 sent Fri 27 Mar 2015:

Keith:

She doesn’t miss/misfire, just hesitates in the following
instance: when I am on the motorway above 4500ish (she still
should have another 1500 to go after that… my series 2 e-
type with strombergs even goes to 5500 with no problem).

Can nail it from naught and get great power even despite the
gearing I’ve got in the rear end… that’s another subject
for another day though.

Other questions:

No air filters, running short v-stacks (probably 2.5’’ long).–
'71 XKE S2
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In reply to a message from rlich8 sent Sun 29 Mar 2015:

I didn’t understand your comment about the maker not being
familiar with Webers as Classic Jaguar Replicas build
practically no other type of car. I would have thought
it’s their job to give you a properly-running car.

Rob Beere should have some ideas too.

However, when it comes down to it I think a fully-
instrumented work-up is in your future and you’re not
going to get anything other than guesswork here. I assume
your ignition has been strobed for full advance.

Pete–
1E75339 66 D, 1R27190 70 FHC, 79 S2 XJ12L
Gaithersburg, Maryland, United States
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I thought I would add to this thread instead of starting another since there are many similarities.

I have a new set of Triple Webers and manifold purchased from Pierce Manifold. They are on an XK 4.2 from a 1975 XJ6 series 2. The engine will eventually go into a D-Type reproduction / replica. For now, it is on a home built run stand in my garage. Specs for engine and carbs…

XK 4.2. —— Recently rebuilt by me back to stock specs. 8:1 compression, stock valves, cams, exhaust headers, etc etc. 20/50 oil

Ignition upgraded to pointless Pertronix mechanical advance with 3 Amp coil.

Ignition Advance is currently set to 15 degrees.

Electric fuel pump with pressure regulator set at 3 and using 93 octane gas.

No transmission attached. Only flex plate and starter. Transmission will be an automatic since I am a double amputee and can’t ‘legally’ drive a standard.

Carbs are new 45DCOE 152s… current settings are…

Idle. 60F9

Main. 135

Emulsion Tube. F2

Aux Venturi. 45. (I took one out, and this was the only number anywhere on it).

Air corrector. Unknown.

So with all of that being said, the engine starts and runs, which was my primary goal in case I screwed something up in the rebuild. I’ve fiddled with it a bit and got it to stop spitting and popping. Average idle mix screws are between 2.5 and 4 turns out, which I’m sure is too much. I can’t seem to get the idle below 1400 rpm without it running rough and wanting to stall.

And all of this leads to my main question…

Is there any point in trying to tune these carbs when the engine is not in a car and won’t be for a while? I’d like to start since I have some time, but if it’s a mostly pointless endeavor, I’d rather not waste my time (or yours) and revisit this thread later on when the car is built and the engine in it.

No real point of doing anything out of the car: it needs to be on an engine dyno, or a rolling road, to fo any really meaningful tuning.

Without the torque converter it might not idle right because there is no flywheel inertia to keep it turning. I think that it is better for the engine if you run and tune it in the car so it won‘t idle too long as a fresh rebuild, sees some load (rings) and I also think you can’t tune it right without some mass.

Thanks. Yeah, that all makes sense. At least I know it runs, and I can fire it up once a week to keep the oil circulated. Much appreciated. I’m sure I’ll have questions when the car is built and ready to drive.

For long term storage, you are better off just cranking it over for oil pressure, and lightly oiling the bores, maybe monthly.

Short running is not necessarily a good thing to do, unless you get it good and hot. Even then, if you live in a humid climate, that can create more condensate issues than it helps.

What about bedding in the rings, and cams/tappets; isn’t it so that we‘re supposed to give it some load and varying rpm to run it in?
I would let it sit as is and crank up the oil pressure without plugs in as soon as it is ready to be installed or together properly so you can run it until it is warmed up.

What was taught to me, about rings: do them SLOWLY. About cams/tappets (new ones) do them FAST.

Eliminating the cam/tappets, as most of the rebuilds of engines I did did not require new stuff, I began the runs SLOWLY, building up to hot.

As for cranking over for pressure, and assuming a new cam/tappet is treated with MoS2 grease, rings nor cam/tappets are affected by it.

What CAN be an issue, and why I recommended periodic cranking over (even if just by hand) is to minimize rusting of the rings to the bores.

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