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Instructions
for
SHOVELHEAD & IRONHEAD XL
42mm Mikuni Carburetor & Manifold Kit
12450 Whittier Blvd., Whittier, CA 90602 Tel:(562) 907-2600 Fax: (562) 907-2606
www.riveraprimoinc.com
REQUIRES 1990-95 OEM BIG-TWIN STYLE THROTTLE CABLES.
THROTTLE CABLE LENGTH IS DEPENDENT UPON HANDLEBAR HEIGHT.
1108-0010 / Revised 3-08
For all Shovelhead applications 1970-1984 and all Ironhead Sportster models 1971-1985.
Pre-1971 model XL cannot be fitted due to the fact that 1958 XLCH used a magneto or distributor located directly
below the carburetor. 1954-to-1970 KH, XL, XLH, XLH-70, and XLCH have a stand-up a distributor located directly
below the carburetor.
* NOT LEGAL FOR SALE OR USE IN CALIFORNIA OR ON ANY POLLUTION CONTROLLED MOTOR VEHICLES.
HOME OF PRIMO® BELT DRIVES
QUALITY & PERFORMANCE SINCE 1973 APPLICATIONS
This installation instruction set applies to the Rivera-MIkuni HSR42
carburetor kits for 1970-1984 Harley-Davidson "Shovelhead" Big-
Twin & 1971-1985 Iron Head XL motorcycles. Intake manifold, all nec-
essary hardware & a high performance Mikuni / K&N air filter are
included. 1990-95 style throttle cable cables are required.
DISASSEMBLY
1) Disconnect the negative (minus) battery terminal.
2) Turn the gas petcock to the off position.
3) Removes the gas tank(s) from the motorcycle or elevate
the rear of the gas tanks for better access to the
cylinder/intake manifold area.
4) Remove the air cleaner assembly including backing
plate.
5) Disconnect the choke cable from the motorcycle.
6) Disconnect the vacuum hoses and gas supply hose from
the carburetor.
7) Remove the carburetor from the motorcycle.
8) Remove existing throttle cables. 1990-1995 OEM style
throttle cables are required.for this installation.
INSTALLATION
1. INTAKE MANIFOLD
A) Attach the enclosed rubber flange to the Rivera intake
manifold with 2 each 5/16" X ¾" bolts & flat washers.
B) Attach the Mikuni intake manifold assembly to the heads
in place of the stock intake manifold. Do not torque the
clamps tight at this time; later, installation of the air cleaner
assembly will bring the manifold into proper alignment.
Please note
Special adapter rings are included to be used on the
intake manifold as illustrated. These rings enable the
use of "rubber-band" style manifold seals and large
diameter clamps. See the following illustration.
2. CARBURETOR INSTALLATION
A) Insert the carburetor spigot into the rubber flange, and
tighten the clamp securely.
3. THROTTLE CABLES
CAUTION
Two throttle cables are REQUIRED for the HSR carb. If
you do not have a dual cable pull-open, pull-closed
throttle cable assembly, you must obtain a dual cable
throttle assembly. Lubricate throttle cables prior to
connecting to carburetor..........
USE 1990-95 OEM throttle cables
A) Route the cables to the carburetor along the right side of
the frame (just like stock). Next, route the cable below the
top motor mount to the carb
B) Connect the cables to the carburetor bracket as shown.
First the pull-to-close cable (idle cable) and then the pull-to-
open cable.
4. THROTTLE CABLE ADJUSTMENT
A) Rotate the throttle grip to the full open position, look into
the throttle bore and see if the throttle valve (slide) opens
completely. If the throttle valve does not open completely
unscrew the adjuster on the opening cable until it does. This
adjustment should be made carefully to assure maximum
carburetor performance. After adjustment tighten the
adjuster jam nut.
B) After adjusting the open cable, adjust throttle freeplay
with the closing (idle) cable to approximately 1/8" an indi-
cated in the following illustration.
note
It is very important to adjust the cables in the preceding
described manner to ensure that the idle cable operates
correctly for safety. It must close the throttle completely
2
PLEASE NOTE
USE CAUTION
PLEASE NOTE
SAFETY WARNING
pull open cable
pull close cable
SHOVELHEAD/IRONHEAD XL
Installation Instructions Check and make sure that the throttle cables are rout-
ed properly by rechecking the throttle play as the han-
dlebars are turned from side-to-side; the amount play
should remain consistent.
C) After the throttle cables have been adjusted, make sure
that all the lock nuts are securely tightened.
5. AIR CLEANER
A) The air filter bracket is attached to the crankcase with 1
long bolt, and a bracket-spacer. Removed the crankcase
nut located between the tappet blocks & replace it with the
enclosed bracket spacer; tighten the spacer securely.
B) Remove the stud protectors from the K&N filter and
place the two backing plates on the studs. Now slip the the
filter onto the carburetor.
C) Attach the 2 long brackets to the air filter studs with the
enclosed nuts & flat washers, and to the bracket spacer with
the enclosed bolt using the lock washers, and flat washers.
When the carburetor and air cleaner are properly aligned,
securely tighten all of the mounting hardware including the
intake manifold clamps.
In some cases it may be necessary to bend the
brackets slightly to arrive at the correct fit.
D) Use the enclosed hose clamps to secure the fuel hose to
the petcock, and the HSR carburetor. The screw clamp
goes on the petcock end and the spring clamp attaches to
the carburetor end.
E) Attach the chrome air filter cover with the enclosed
socket head screw.
7. CHOKE CABLE INSTALLATION
A) Attach the Mikuni choke cable bracket to the original
choke cable bracket on the air cleaner stud with the enclose
hardware as illustrated.
B) Route choke cable to it's mounting bracket and tighten
the jam nut securely. After the cable is securely fastened,
adjust choke cable to have 1mm (.040") of free play with the
adjuster located under the rubber cover at the carb.
8. OVERFLOW HOSE
A) Route the carburetor overflow hose between the push
rod tubes and the rear cylinder, then downward towards the
frame.
9. STARTING
Reconnect the battery and reassemble the remainder of
the motorcycle. Turn on the gas, and start the motorcycles
as you would normally. After the motor has warmed up,
adjust the idle to the desired RPM.
CAUTION
To properly maintain the HSR42's superior high
performance capabilities, it is recommended
that the air cleaner be inspected at 5,000 mile
intervals. Clean/replace the filter as needed.
3
USE CAUTION
use the new case bolt included in the kit!
USE CAUTION
SHOVELHEAD/IRON HEAD XL
Installation Instructions
spacer 4
Parts list for HSR42mm Mikuni
Part #
Description Qty.
990-662-002 Choke Cable Assembly
1
HSR42/012
Air Cleaner
1
HSR42/018-42
Rubber Flange
1
HSR42/021-250
Cover A/C (CHR)
1
HSR42/027
Bracket, Air Filter
2
1043-0004
Carb Assembly
1
N100.604-155
Main Jet#155
1
N100.604-165
Main Jet#165
1
RE-0069
Bracket spacer
1
RE-AD-8183
Manifold Adapter
2
RIV-002
Bolt socket head
for rubber flange
2
RIV-0029
Lock Washer, 5/16"
4
RIV-003
Center Case Bolt
1
RIV-0045
Flat Washer, 5/16"
6
RIV-005
Choke Bracket
1
RIV-0061
Manifold
1
RIV-007
5/16" AN Flat Washer
2
RIV-017
Fuel Line 2 feet
1
RIV-0070
Cable Bracket
1
RIV-020
Clamp, Hose
2
RIV-201
Nut, 5/16"18
2
RIV-202
Bolt, 5/16"18 x 3/4"
1
RS36/47
Plate, Back
2
RS36/54
Screw, Cover
1
TMX/0032
Clamp, Hose
1
SHOVELHEAD/IRON HEAD XL
Installation Instructions 5
MIKUNI HSR42 CARBURETOR
HSR42'S TUNING CIRCUITS & HOW THEY
WORK:
IDLE CIRCUIT (PILOT SYSTEM)
The idle circuit supplies fuel at idle speeds & has a big influ-
ence on fuel flow up to 1/4 throttle. There are three tunable
parts in the idle circuit:
1). PILOT JET-controls maximum fuel flow thru the idle circuit.
2). PILOT AIR JET-controls the maximum amount of fuel that
will flow thru the pilot jet by allowing a higher (smaller air jet) or
lower (larger air jet) vacuum signal at the pilot jet.
3). PILOT SCREW-controls how much fuel is allowed to enter
the carburetor venturi.
The pilot screw is used to control idle mixture. Turn the screw
out to richen the idle mixture. Turn it in to lean the mixture. The
engine should have a smooth, steady idle with the screw
between 1/4 and + 3-1/2 turns out from fully bottomed (gently!).
If the engine requires more than three turns out, the pilot or
pilot air jet may be too lean. If it requires less than 1/4 turn, it
may be too rich.
As the throttle is opened the pilot screw's position becomes
less important than the size of the pilot & pilot air jets. A larger
pilot jet richens the mixture from just off-idle to 1/4 throttle. A
smaller one leans it. A change in pilot air jet has the reverse
effect. A larger pilot air jet leans the mixture and a smaller one
richens it. The pilot jet & pilot air jet have slightly different
effects on mixture strengths. These effects are discussed in the
"General Tuning Procedure.
The idle circuit is adjusted by changing either the pilot or the
pilot air jets. A one-size larger pilot jet will have nearly the same
effect as a one-size smaller pilot air jet. It is generally easier to
change the air jet since