Select a screw the proper length to end up flush with the
inner veriiuri bore. Grind down the center threads on the
screw to allow fuel to pass in the idle circuit. Install the
screw with Loctite sealant.
An air inlet plate can be fabricated from 318 inch
aluminum plate if a smoother inlet horn is desired. This
is machined out to match the carburetor inlet opening
and then radiused to a smooth inlet shape with a die
grinder. If this is used, the main jets must be increased to
1.451nm on both sides.
Duct air from the left side air scoop to the carburetor,
but don't attempt to pressurize the carburetor with this
air as this would adversely affect the
airlfuel ratio.
The original choke valve shaft holes in the carburetor
air horn can be plugged by tapping them with a 1/4-28
tap and screwing bolts into them. Seal the threads with
Loctite.
Intake Manifold
A
number of different intake manifolds have been used
on the X1/9 cars. The best stock manifold is the Fiat
P/N 4425 193. This manifold should be used as the engine
is quite sensitive to the available intake flow area. Match
the manifold to the enlarged intake
polts in the modified
cylinder head.
built in or
28" measured at the crankshaft. If the PBS
modified production racing head and pistons are being
used, the total advance required will be between 30°and
33Oat the crank. Thus, a static advance of 2"to 5"should
be about right. The actual advance curve is not critical for
racing since the useable power curve is all above the rpm
where full advance is reached. However, starting may be
enhanced somewhat by restricting the total amount of
advance in the distributor so that an initial static advance
of
10" to 12 can be used while not exceeding the 30' to
33" at full speed.
Another approach which can be taken is to build a
special distributo~ with no advance mechanisrri. This dis-
tributor can be fitted with two sets of ignition points
which are timed 10°to 12' (crank) apart. Then the re-
tarded set of points can be selected by a relay which is
triggered from the starter switch. This way retarded timing
is used to start and as soon as the starter button is released
the ignition switches to full advance. The fixed mechan-
ical advance distributor has a more stable timing pattern
than the stock distributor, but this advantage is somewhat
offset by the added electrical complexity plus the extra
set of points required.
Thc stock radio suppression secondary (plug) wires
should be replaced with high quality wire core leads.
IGNITION SYSTEM
Several options are possible for the ignition system. The
1300 XI 19 engines have a conventional type ignition sys-
tem with points and a standard coil. This system can be
modified in several ways to improve its racing perform-
ance. The 1500 XI 19 has a Bosch electronic ignition sys-
tem which works well up to about 7000 rpm. For higher
rpm use, the electl.onics must be changed.
1300
Ignition System
The stock point-type 1)ucellier distributor is basically a
good unit if it is in good condition. But a few changes are
necessary for racing.
The vacuum retard unit should be disconnected for
racing. However, if the vacuum retard diaphragm assembly
is physically removed, the stationary point holder must
be tack welded in place.
The stock coil should be replaced with a higher energy
coil. If the replacement coil
I-equiles a series, primary re-
sistor, this must be added since the Fiat system doesn't
have one.
If desired. a high quality electronic ignition and a
matched coil can be added to the system. Don't attempt
to use a stock point-type Fiat coil with an electronic ig-
nition. If an electric tachometer is used, check the com-
patibility of the electronic ignition and the tachometer.
The stock distributor has
14" of mechanical advance
1500
Ignition System
The stock Bosch magnetic-pick-up-type distributor has
an excellent timing pattern but the electronics box with
it is not suited for racing.
The stock Bosch distributor can be used without
modification other than disconnecting the vacuum ad-
vance unit and restricting the total advance to enhance
starting. This should be restricted to
1O0total advance at
thc distributor by welding
up
the inboard advance weight
stop. This allows a static timing setting of about 14Oad-
vance (crankshaft) for a total advance of 34"maximum
at the crank.
The Bosch electronics limit the spark voltage at high
rpm (above 7000 rpm). This is adequate for the stock
engine but not for racing. PBS offers a replacement elec-
tronics unit which has been specifically matched to the
Bosch distributor and coil. This unit works flawlessly to
10,000 rpm. The electronics package can be located in
the spare tire well which will protect it from engine heat
and be close to the distributor.
EXHAUST SYSTEM
Four branch tuned exhaust headers are necessary for
either size
X1/9 engine for racing. Exact dimensions don't
seem to be extremely critical, but they should be large e-
noughin diameter to minimize restriction and long enough
to make the effective tuned length occur at a useable rpm.
Primary pipes of 1-318 inches O.D. by about
26
inches
long seem to work well. The collector size should be about
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