Basic Maintenance on your R75/5

By Tom Cutter

Page adapted from airheads list email. Included here with explicit permission.

I would do the services on your R75/5 in this order:

  1. Change ALL oils.
  2. 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.
  3. 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.
  4. 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).
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. 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.
  10. 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.
  11. 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 post.
  12. 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 other models).
  13. 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 work.

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 the cables.

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.