5 Often-Missed Maintenance Jobs on Vintage Honda Motorcycles: Rear Brake, Gas Cap, Petcock, Handlebars, and Exhaust Crush Gaskets

This guide walks through five maintenance jobs we commonly see overlooked on vintage Honda motorcycles, plus the key things to check for to resolve these problems:

• Rear brake pedal height adjustment

• Rear brake travel adjustment (drum rear brake)

• Gas cap seal replacement

• Petcock inspection, cleaning, and reassembly tips

• Handlebar riser bushing replacement and clamp orientation

• Exhaust gasket replacement and correct collar orientation

Note: The examples shown were demonstrated on a Honda CB350 and a Honda CB360 fuel tank, but the same concepts apply across many vintage Honda motorcycles with similar components.

Tools

• 12 mm wrench/socket (handlebar clamp bolts; exhaust flange nuts on the example shown)

• Basic hand tools (flathead screwdriver, pliers)

• Wire brush (for gas cap corrosion/rust cleanup)

• Small flathead screwdriver or pick (to remove exhaust gaskets)

Parts

• Replacement Gas Cap Seal

• Petcock O-rings, Filter Screens, and Complete Replacement Petcocks

• Handlebar Riser Bushings (for CB175, CB200, CB350K, CB360, and CB450 families of motorcycles)

• Exhaust Header Gaskets

1) Rear brake pedal height adjustment 

Symptoms of incorrect rear brake pedal height

• Too high/tight feeling: you may accidentally apply brake while riding while being very easy to lock up the rear wheel. You may feel your foot is uncomfortable because your toe is pointed up while attempting to not depress the pedal when riding.

• Too low/awkward: slower reaction time and less consistent braking control. A feeling that you have to depress your toe too far down to feel the brake engagement. 

Steps

1. Put the motorcycle on the center stand on stable ground so you can sit on it normally.

2. Find the rear brake pedal height adjustment screw and lock nut.

3. Loosen the lock nut.

4. Turn the adjustment screw clockwise or counterclockwise until your foot rests comfortably on the pedal.

5. Tighten the lock nut to hold the setting.

Tip: The adjustment hardware location can vary by model. On the example shown (CB350), it is near the pedal, but some models place it slightly differently. Some models do not have a pedal adjustment screw. 

2) Rear brake adjustment

Why rear brake travel matters on vintage Hondas

A rear brake that locks up with very little pedal movement is harder to modulate—especially in a panic stop. Increasing travel gives a wider, safer range to apply braking force before lockup.

Steps

1. Move to the rear of the motorcycle and locate the rear brake adjuster nut on the threaded rod.

2. Loosen the adjuster nut to increase pedal travel (looser brake).

3. Tighten the adjuster nut to decrease pedal travel (tighter brake).

4. Re-check pedal feel and confirm you can apply the brake progressively without immediate lockup.

If you run out of threads on the adjuster

If the adjuster is nearly maxed out or you have excessive threads showing, reset the brake arm position:

1. Remove the bolt that clamps the rear brake pivot arm to the spline shaft.

2. Move the arm a spline or two forward or backward.

3. Reinstall and tighten the clamp bolt.

4. Set final travel using the rear adjuster nut.

Reference check:

• With the brake fully released, the threaded rod should sit near the rear edge of the pivot arm on the example shown.

• Target rear brake arm travel: 0.8–1.2 in (20–30 mm).

3) The gas cap seal

When to replace the gas cap seal

Replace the gas cap seal if you see fuel seepage, staining, or if the rubber feels hard/brittle. In our video example, the seal looked “OK” until removal revealed it was brittle.

Steps

1. Remove the gas cap.

2. Remove the old seal from the cap.

3. Clean corrosion or rust from the gas cap sealing area with a wire brush.

4. Carefully stretch the new seal over the cap.

5. Confirm the seal orientation: the thin side faces up toward the inside of the gas cap.

6. Reinstall the gas cap and check for leaks.

Heads up: Installing the new seal can take longer than expected—work it on evenly so it seats fully.

Note about the locking gas caps

The standard locking gas cap used on many vintage Hondas, as is shown in the video is not actually keyed, it just looks that way.  Anything that is key shaped (aka a screwdriver) can open it up.

4) Clean and rebuild the petcock

Common petcock problems we see

• Clogged petcock: not enough fuel flow

• Missing/damaged filter screen: too much debris getting through and clogging small passages in the carburetors

Steps

1. Drain the gas tank safely.

2. Remove the petcock from the tank.

3. Open the petcock and inspect internal parts and screens.

4. Clean all parts thoroughly.

5. Replace worn O-rings or damaged filters/screens as needed.

6. Reassemble carefully using the tips below.

7. Reinstall the petcock on the tank and check for leaks and proper flow.

Petcock parts

• Main mounting nut

• Petcock body

• Sediment bowl

• Lever

• Wavy washer

• Faceplate

• Mounting screws

• Main filter

• Lever 4 hole seal

• Tank-to-petcock seal gasket

• Sediment bowl O-ring

• Small mesh filter on the reserve line (often missing on original petcocks)

Reassembly tips

• Do not pinch the wavy washer between the petcock body and the faceplate. 

• Install the mounting nut back onto the petcock with the smooth side up.

• Thread the mounting nut onto the petcock counterclockwise (it has reverse threads) only about a half-turn before installing to the tank. When installing to the tank: hold the petcock in position and turn only the mounting nut. It is designed to draw both sides in evenly and seal on the rubber gasket. Tighten snugly but do not over tighten.

If the brass fuel nipples pull out

A few taps with a copper or plastic mallet can seat the brass fuel line nipples back into the petcock body.

5) Handlebar riser bushings

Why handlebar bushings matter

Handlebar bushings dampen vibration. When they’re worn out, they can create a vague or unstable handling feel and a potentially unsafe condition.

Steps

1. Loosen the four 12 mm bolts that hold the handlebars in place.

2. Push the handlebars out of the way.

3. Remove the nut on the bottom of each handlebar riser and slide the risers out to access the bushings.

4. Replace the top and bottom bushings on both risers (four bushings total).

5. Reinstall risers and handlebars.

Two critical reminders

1. If your motorcycle has a grounding wire attached to the handlebars, reattach it during reassembly.

2. Handlebar clamps are asymmetrical on the setup shown:

   • Install with the small dot facing forward

   • Tighten the front riser bolts before the rear bolts

   • You should end up with a small gap at the rear of the clamp when installed correctly

6) Exhaust gaskets

Why exhaust gaskets matter

Old, leaky copper and composite exhaust gaskets can cause exhaust leaks that negatively affect running conditions.

Steps

1. Unbolt the nuts on each exhaust flange.

2. Remove the mounting fasteners that connect the muffler bracket to the frame.

3. Remove the exhaust pipes.

4. Locate the exhaust gaskets in the cylinder head. Gaskets may be hidden by carbon buildup. Clean or scrape carefully as needed to expose them.

5. Pry out the old copper or composite exhaust gaskets with a small flathead screwdriver.

6. Install new exhaust gaskets.

7. Reinstall the exhaust with correct collar flange orientation. 

   1. The exhaust collar’s curved side faces the exhaust flange.

   2. The collar’s thin side faces toward the engine, helping push the pipe into the gasket.

8. Tighten fasteners snug, but not excessively tight. Copper and composite gaskets crush to conform and seal. If you crush them too far, you can cause leaks again.If installed correctly and not over-crushed, these gaskets can often be reused 3–4 times.

Troubleshooting

Fuel still leaks from the gas cap after replacing the seal

• Re-check seal orientation (thin side toward inside of cap).

• Verify the cap sealing surface is clean and free of corrosion.

Petcock leaks after rebuild

• Confirm the wavy washer is not pinched between the body and faceplate.

• Inspect O-rings for nicks or improper seating.

• Confirm the large nut was tightened snugly and seal was properly sandwiched in between the tank and petcock body using the technique shown in the video.

Exhaust leak after gasket replacement

• Confirm the old gasket was fully removed (they can stick in place under carbon).

• Confirm collar orientation (curved side to flange, thin side to engine).

• Loosen and re-seat the pipes evenly before snugging the flange nuts.

FAQ

What rear brake travel should I aim for?

On the example shown, Honda’s expected rear brake arm travel is 0.8–1.2 in (20–30 mm).

Should I add inline fuel filters instead of rebuilding the petcock?

In our testing, we have found inline filters to limit fuel flow to the carburetors and cause running issues over 5,000 RPMs. Because of this, our recommendation is to clean and rebuild the petcock and gas tank so fuel flow and filtration are correct at the source, instead of using inline filters as a patch.

Do I need to replace exhaust gaskets every time I remove the exhaust?

Not always. Copper/composite exhaust gaskets can often be reused 3–4 times if they weren’t over-crushed and are still sealing properly.

My Horn and Starter are not working after replacing the handlebar bushings?

The small ground wire on the bottom of the handlebar riser transfers ground signal from the handlebar switch boxes to the motorcycle body. This must be in place for the horn and starter button to properly function on the OEM Honda switches.