What I have got here is by no means the laws of webber tuning. The state of tune of an engine has a huge
impact on your carby settings. Please use this as a guide only.
My Car:
I origionally bought my L20 1600 with a set of twin 48ml carbies on it. It also
origionally has a set of 4-1 extractors. This caused the car to bog down heavily
when trying to start quickly at low rev's, pretty scary when pulling out intotraffic.
I spoke to my local workshop and he had a guy with a 2.4L 1600 with twin 45's
looking for a set of 48's. We did the swap and At the same time the 4-1 extractors
were swapped for a set of pacemaker 4-2-1s. This caused much improved
midrange power and absolutly no sign of bogging.
I thought I would check out my webbers and see what kind of settings they had, this is what I found:
Carby: 2x 45 DCOE 13
chokes: 36
Aux vent: couldn't get out.
Main jet: 150
Air corrector: 160
emulsion tube: F15
idle jet: 50 F9
acc pump jet: 50
I spoke to the ozdat list and was given a few ideas.
Your setup sounds like a decent starting point, if a little on the rich
side.
Does it blow black smoke at full throttle and high revs?
To lean it out a bit, you can drop down one or two main jet sizes. This
leans out throughout the whole rev range from about 2k+ RPM (i.e. when
the main circuit becomes active). You can also/instead go a few sizes
larger in the air correctors. This leans out the top end (say 5000+) and
has little effect on the low end. The main jets are more sensitive than
the air jets, so you generally need to go at least 10 bigger on the airs
to notice a clear difference. I would probably drop down to a 145 or 140
main and go up to a 170-180 air corrector to start with. Also, your
accelerator pump jet is unnecessarily large and is just pumping fuel out
the exhaust each time you floor it, drop down to a 40 if you can.
Tuning blind is no fun, and can be risky... So I strongly recommend you
get hold of an air/fuel ratio meter first and at least check what your
existing mixtures are like, or even better get it on a dyno.
Here's my setup for reference:
L20B, 76 deg cam, .595" valve lift, big valves, big exhaust, 10.5:1 comp
45 DCOE 13's
Chokes: 36
Aux vent: 4.5
Main Jet: 140
Air Corrector: 185
Emulsion: F2
Idle Jet: 50F9
Pump Jet: 40
Plugs: NGK BPR7EIX
B/B electronic dizzy
15 BTDC
I arrived at these settings after spending a day driving around with an
Autronic wide band A/F meter shoved up the pipe and a full set of Weber
jets, chokes, vents etc. to try things out. It is set up safely rich at
the moment. The hardest area to get right is the progression from idle
to main circuits. The major factors influencing this area are
progression holes, emulsion tubes and idle jets.
I tried 38mm chokes which were marginally better up top but lost out a
bit down low. 34mm choked the top end too much.
A major factor is which actual Weber bodies you have. The progression
holes which are uncovered on slight throttle are drilled into the body
and differ between different 45's. The carb has a number after the DCOE
(i.e. 45 DCOE 13) which indicates which progression holes the carb has
as well as some other minor differences throughout the DCOE series (i.e.
some carbs have idle air bypass passages whereas others don't, some
carbs have progression holes accessible via a removable screw whereas
others have a pressed in brass welch plug covering them instead) For
this reason it is advisable to use a matching set. I have found that the
stock progression holes in a 13 body are a bit weak and you need to
compensate by running one size larger idle jet (50) than really
necessary in order to cover the lean spot in the transition.
IGNITION TIMING:
As for the static ignition timing, this really depends on your dizzy and
what it's advance curve is like. What dizzy do you have? More important
than the static figure is how much total advance there will be once the
centrifugal advance in the distributor has come in (i.e. at high rpm). I
always check the total advance with a snap on timing light that you can
delay the flash by a certain no of degrees. You hold it at about 4500
revs and delay the flash (with a button on the timing light) until it
lines up with the TDC mark. You can then read the amount of advance off
the timing light LED display. I found around 35 degrees of total advance
is good for a hot L series with twin carbs. With a S2 bluebird dizzy,
this usually ends up at about 15 BTDC static timing. Running this much
advance is pretty hard on the starter motor and can make it pretty hard
to turn over. L6 starters work great though, no need for an expensive
reduction starter. (Thanks Tom :) Also I would remove the vacuum advance
if it has one, these only work properly with webers if you get a vacuum
port from each runner and join them all up.
Chris Howard
Mick Ralph's setup
My L20 has big valves 76 cam and fairly open exhaust system
My settings were
Venturi 36
Main Jet 150
Air correction jet 150
Emulsion Tube F2
Idle Jet 45 F9
Pump Jet 40
Plugs BP6EY
Std B/B electronic dissy - no vac advance
15 BTDC
This set up is very similar to yours but recently because of discussions
with terry and the list and some help from a guy called MOTACARB here in
nerang, I now run slightly smaller mains #145 and much larger airs #190
with really good results. I'm also considering going up again with the air
jets just to try it out. The engine revs much sharper now and doesn't bog
down so much below 3500rpm, like it used to a bit. Trouble is it still
doesn't want to rev right out to 7000 like it used to. I'm gonna build a
better bottom end before i go any further here.
For anyone interested in weber parts this guy at Motacarb sells airs and
mains @ $5.00 +gst.
Mick Ralph
Mick, your setup seems to be pretty rich, I bet if you put some bigger
air correctors in it would pull hard to 7000. Might be worth borrowing a
dyno and/or A/F meter. I had 150 airs in and it was running 10:1 A/F in
the top end... Going up step by step made it better all the way... Now
it's running a conservative 12:1 up top, and doesn't want to stop at
7000 :)
Chris Howard
