I would do the services on your R75/5 in this order:
- Change ALL oils.
- Torque cylinder heads (25 foot pounds, loosen each nut 1/2 turn,
then torque, use crisscross pattern)., adjust rocker arm end play (zero
play, no rotational binding), adjust valve clearances (cold engine) to
.006" Intake, .008" Exhaust.
- Service auto advance unit (don't snap the thread off the end of the
cam, tighten GENTLY!), grease point cam felt with a smear of grease.
- Set points gap to 0.016" (0.40 mm) using a good feeler gauge, or
better yet a dwell meter, look for 39 degrees on the four cylinder
scale (gives you 78 degrees on a two cylinder).
- Set ignition timing static setting to S mark on flywheel.Check full advance timing at 3200 RPM, the dot (or hole if the paint
is gone) above the F mark should be steady in the center of the timing
hole, aligned with the machined groove in the side of the hole.
- Service the air filter, i.e., put a new one. DO NOT blow out air
filter with compressed air, do not leave a K&N filter in at all.
- Drop carb float bowls and clean the tiny jet in the little well in
the corner of the bowl using a single strand of wire from a wire brush,
held with needle nose pliers. Make sure contact cleaner will spray
through the jet into the bowl.
- Remove the main jet and jet holder (make a mental note of the depth
of engagement of the jet holder), drop down the needle jet and emulsion
tube, (keep your finger over the hole so they don't fall out and get
lost.) Use some Gumout carb cleaner spray to clean the gunk that has
accumulated above the jet holder. Spray the jets and emulsion tune
clean, then reinstall the emulsion tube, needle jet and jet holder.
Visually align the jets onto the needle carefully. As you screw the jet
holder up in with your FINGERS, if it doesn't seat fully (remember the
mental note?) then back it up about 1/32 of a turn and wiggle it as you
screw it in gently (FINGERS ONLY!) You will feel when the emulsion tube
finds its way up into the carb body hole. If you can;t get it , remove
the air tube from the air cleaner housing and visually see that the
emulsion tube projects up into the venturi about 3-4 mm. You can wiggle
the needle to help align it as you screw it up in with your FINGERS.
- Check the float level setting by lifting the float gently with your
fingers. When the needle seats, BEFORE the spring loaded part begins to
depress, the seam in the float should be parallel to the float bowl
gasket surface. Reinstall the bowl carefully, making sure the gasket is
fully seated in the groove all the way around.
- Check that the throttle cable has a tiny amount (1-2mm) free play
when the throttle grip is all the way back. Get the two sides as close
to the same free play as possible.
- Check that the choke cable fully seats the lever on the post when
the lever is in the horizontal position. At half choke, the lever on
the carb should be halfway between the posts. At FULL choke position of
the hand lever, the choke lever should be all the way up to the top
- LIGHTLY screw the idle mixture screw IN until you feel the screw
seat. Now back the screw OUT by 3/4 turns (this setting varies for
- Turn the idle SPEED screw OUT until it does not contact the
butterfly lever at all. Now screw the screw IN until it JUST touches
the lever, now turn it IN one FULL turn.
These are the baseline settings. Now take the bike for a LONG test
ride, at least five miles, to get it to FULL operating temperature.
Riding around the block or starting and revving on the stand will NOT
At this point you need to synchronize the carburetors. This is
accomplished either by shorting one cylinder at a time (this takes some
practice to get right, usually you need somebody to show you once) or
using a vacuum gauge on the vacuum takeoff ports on the side of the
carb. Set the idle mixture on each carb at the point that gives best
running, usually between 1/2- 1-1/4 turn out. Balance the idle speed
screws, then balance the cable pull off idle. Recheck to be sure that
you still have a tiny bit of free play of the cables. If not, readjust
This should get the bike running pretty well. Idle speed should be
at 1000-1100 RPM. DO NOT set the idle for a super low "tickover", as
this will severely reduce oil circulation in the engine and make the
transmission rattle like a bag of rocks.