Help tuning Weber 40DCOE carbs
gibb...@astro.pc.ab.com
Weber 40DCOE carbs...
I have a 2.5L 6 cylinder engine (on a '74 Triumph TR6) fitted with 3
Weber 40DCOE dual side-draught carbs (yes, 1 carb per cylinder).
The problem: low end performance. Coming off of idle to about 2000 RPM is
touchy at best. No power at all in this range.
Where I am at now:
Using the Colortune kit (basically a sparkplug with a clear insulator so you
can see the color of the flame in the cylinder as the engine is running) I
have gotten the medium to high end performance to be outstanding. Flame color
is a nice bunsen blue with a slight tinge of white (this is where the Colortune
kit suggests you be). But the low end is still a bright yellow color (way too
rich).
I tried the carb jet settings as suggested in the "Haynes Weber Carburetors"
manual and found the settings to be way too rich. Yellow color flame
throughout all engine speeds. That is when I started experimenting and got
the high-end performance to where I like it.
As it stands now, this is where the jetting on the carbs are now:
Main Jet: 120 Air Corrector Jet: 160 Emulsion tube: F11
Choke Tube: 26 Aux Venturi: 45 Idle Jet: 50F11
Accel pump Jet: 40 Accel pump Intak/Dis Jet: 50 Accel Pump Stroke: 10mm
Since the idle jet is responsible for the low end performance (idle thru
the progression stages until the main circuit kicks in), I am planning to try
a 45F11 idle jet. Is this consistent with any of your Weber Guru's experience
out there?
I guess what I am looking for is someone who has successfully tuned a set of
Weber 40DCOE's in a similar application and can give their jet selections
that they found to work, plus any notes about 'flat spots' or other anomalies
of the carbs. Thanks in advance for your help!
signed,
John 'Brass jets coming out the wazoo' Gibbons
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Paul Collins
> I am looking for someone who has had some experience in tuning
> Weber 40DCOE carbs...
>
> I have a 2.5L 6 cylinder engine (on a '74 Triumph TR6) fitted with 3
> Weber 40DCOE dual side-draught carbs (yes, 1 carb per cylinder).
You could try talking to Triumphtune on +44 81 948 6668, or FAXing
them on +44 81 940 9268.
Hope this may help,
Paul Collins
John E. Upham
> From article <300.26...@astro.pc.ab.com>, by gibb...@astro.pc.ab.com:
> > I am looking for someone who has had some experience in tuning
> > Weber 40DCOE carbs...
> >
> > I have a 2.5L 6 cylinder engine (on a '74 Triumph TR6) fitted with 3
> > Weber 40DCOE dual side-draught carbs (yes, 1 carb per cylinder).
> >
Sounds like a nice car ! Unfortunately my experience with
Webers and Dellortos ( I have twin 45DHLA's on a 1690 cc Ford
crossflow) leads me and most others I think to the conclusion
that the only way of satisfactorily setting these things up is
either
1 An engine dynomometer or `dyno' if you have the engine out or
2 On a `rolling-road' if the motor is in the vehicle.
This is because the behaviour of the engine alters when under load
i.e. pushing the car along. The rolling-road simulates this and will
give a full readout of %CO, hydrocarbons, torque, horsepower and
other things continuously i.e. at all engine speeds.
When i set mine up we get everything else right first...
1. valve clearences
2. Distributor setting (including dwell angle and timing)
3. plug type
4. fuel pressure (you'll be surprised perhaps about this)
5. air flow onto carbs. How do you think the air flow resembles the
real thing when the vehicle is static ? This affects a few things.
6. air temperature and moisture content affects power
7. note tyre pressures on rolling road.
ok so there are a few factors.
Make sure your Webers are fitted with some sort of isolation from
vibration system. Either use Coswoth rubber thackeries or steel
ones. The latter break when too tight. They are there to stop
fuel frothin cause by resonace
now having cleaned your air filters (hopefully these are K + N or
Pipercross) as I assume you're not running open ram pipes on the
road but you should keep the ram pipes within the K an N's
We can begin....
The rest is down to the rolling road man.
I got just under 150 horsepower on a warm day (doesnt help) from my
engine. I guess the proper TR6 lump will give 150 in standard form
with bags of improvement possible.
You could try fidling with jets yourself but I wouldn't. Very
car preparation people will leave the carb setting to a rolling road
but maybe you could stumble on the right settings yourself. The
problem is expense especially when swopping over choke tubes (you
have six of these !), emulsion tubes and all the other gear. Your
money would be more wisely spent on a couple of hours on a
competant rolling-road where they have all the right bits and
analysis equipment than a week trying yourself.
Believe me. I've been there !
John Upham, (Chemical Physics Ph.D)
University of Sussex, Brighton, UK.
Email: kapn1%cluster.s...@uk.ac
johnu%syma.su...@uk.ac
TVR Car Club member.
Jim Munro x2497
>> I am looking for someone who has had some experience in tuning
>> Weber 40DCOE carbs...
>>
>> I have a 2.5L 6 cylinder engine (on a '74 Triumph TR6) fitted with 3
>> Weber 40DCOE dual side-draught carbs (yes, 1 carb per cylinder).
>
I remember that the 40DCOE has no adjustments other that throttle
and idle mixture.
First, set all idle screws to approcimately the same setting.
Second, by using a carburettor vacuum gauge or by using a
'listening' tube, adjust all three throttles on the common
shaft until they sound identical or have the same vacuum reading.
Then individually tune the idle mixture by making the mixture
richer until the engine starts to stall, and then lean it out
until you get the highest idle speed.
After this, you may have to readjust the throttle setting
to get a correct idle speed. Finally, recheck the throttles with
a listening tube. They should still sound the same.
Ifyou want to go beyond this and start substituting different jets,
venturis etc, you need the assistance of a real expert. There is
a specialist carburretor shop in London called 'xxx carburettor' who
specialise in webbers, but I forget the correct name.
Perhaps someone in England can supply the name.
Jim Munro
Carl William Traber
>>From article <300.26...@astro.pc.ab.com>, by gibb...@astro.pc.ab.com:
>>> I am looking for someone who has had some experience in tuning
>>> Weber 40DCOE carbs...
>>>
>>> I have a 2.5L 6 cylinder engine (on a '74 Triumph TR6) fitted with 3
>>> Weber 40DCOE dual side-draught carbs (yes, 1 carb per cylinder).
>>
> From my dim and distant memories of tuning my old Lotus Cortina
> I remember that the 40DCOE has no adjustments other that throttle
> and idle mixture.
From my even dimmer recollections of tuning the two 40DCOE18 carburetors
on my old Lotus Elan S2, assisted at that time by having the correct
manual, one of the adjustments you haven't mentioned is the carburetor
float level. Unfortunately, I recall that it was a fairly critical
adjustment since it determined how closely the idle and main jets
would be performing vis-a-vis the "proper" mix for the selected set.
If the carbs have been bounced around, or have been transported on
anything other than the vehicle in question (e.g. shipped), or if
the shock isolation mounts were in bad shape, then this adjustment
probably should precede any of the others. On the other hand, if
the carbs are working well and within sync tolerance, then the float
levels are probably OK and the other tuning advice should stand as-is.
-- Carl Traber
Mark Bradakis
[Desription of 3 x 40DCOE setup on Triumph 2.5 liter]
>The problem: low end performance. Coming off of idle to about 2000 RPM is
>touchy at best. No power at all in this range.
What else, if anything, has been done to the engine? Is it an earlier car
with the single exhaust pipe, or a later (about mid 72 on) car with the dual
system? How's the timing, the compression?
>As it stands now, this is where the jetting on the carbs are now:
>Main Jet: 120 Air Corrector Jet: 160 Emulsion tube: F11
>Choke Tube: 26 Aux Venturi: 45 Idle Jet: 50F11
>Accel pump Jet: 40 Accel pump Intak/Dis Jet: 50 Accel Pump Stroke: 10mm
At one time I had set up a TR6 motor (in a TVR) with slightly larger jets,
perhaps 125 main, 175 air, 27 mm chokes, and 140 idle jets. I can't seem to
find the notes just at the moment, so I can't say for sure. But then, all
my Weber experience is for motors usually run in Salt Lake, at 4600 feet
above sea level. A bit different than the < 1,000 foot elevation of Ohio.
Still, I'll try to find the notes and see the exact settings for the 2.5
motor.
At any rate, assuming that the idle mixture screw is adjusted properly there
may be an improvement in coming off idle with smaller idle jets. But one
really needs to do some accurate testing, using a chassis dyno (rolling road),
a G-Analyst or Vericom, at the very least a lot of runs with a stopwatch.
Do you have any F16 emulsion tubes, or have you also tried changing those? Do
you have another small flat spot at just around 3,000 rpm?
mjb.
"The tank is full, the switch is on.
The night is warm, the cops are gone."
John E. Upham
>From article <300.26...@astro.pc.ab.com>, by gibb...@astro.pc.ab.com:
>I am looking for someone who has had some experience in tuning
>Weber 40DCOE carbs...
>I have a 2.5L 6 cylinder engine (on a '74 Triumph TR6) fitted with 3
>Weber 40DCOE dual side-draught carbs (yes, 1 carb per cylinder).
Dear John,
Sounds like a nice car ! Unfortunately my experience with
Webers and Dellortos ( I have twin 45DHLA's on a 1690 cc Ford
crossflow) leads me and most others I think to the conclusion
that the only way of satisfactorily setting these things up is
either
1 An engine dynomometer or `dyno' if you have the engine out or
2 On a `rolling-road' if the motor is in the vehicle.
This is because the behaviour of the engine alters when under load
i.e. pushing the car along. The rolling-road simulates this and will
give a full readout of %CO, hydrocarbons, torque, horsepower and
other things continuously i.e. at all engine speeds.
When i set mine up we get everything else right first...
1. valve clearences
2. Distributor setting (including dwell angle and timing)
3. plug type
4. fuel pressure (you'll be surprised perhaps about this)
5. air flow onto carbs. How do you think the air flow resembles the
real thing when the vehicle is static ? This affects a few things.
6. air temperature and moisture content affects power
7. note tyre pressures on rolling road.
ok so there are a few factors for you to consider.
Now, having cleaned your air filters (hopefully these are K + N or
Pipercross not crummy old pancakes), as I assume you're not running
open ram pipes on the road we can begin....
The rest is down to the rolling road man !
I got just under 150 horsepower on a warm day (doesnt help) from my
engine. I guess the proper TR6 lump will give 150 in standard form
with bags of improvement possible.
You could try fidling with jets yourself but I wouldn't. Very
car preparation people will leave the carb setting to a rolling road
but maybe you could stumble on the right settings yourself. The
problem is expense especially when swopping over choke tubes (you
have six of these !), emulsion tubes and all the other gear. Your
money would be more wisely spent on a couple of hours on a
competant rolling-road where they have all the right bits and
analysis equipment than a week trying yourself. If you think you
have the right bits but some adjustment is neccessary (i.e. float
levels, mixture settings) than you might stand a reasonable chance
but if you are going to err than err on the rich side rather than
lean. Running too rich will just wash the bores, wreck rings and
lower compression, too lean will waste a valve and/or a piston or
two.
ly...@wums2.wustl.edu
which has suggested jet/emulsion tube sizes which are far closer
than the Haynes Weber manual's reccomendations. The Haynes manual
is extremely good as a technical reference, but for some reason
their jetting reccomendations are way off for every car that I
know about.
Cheers,
John