How to Bleed and Replace Brake Fluid on a 1990 Yamaha YFM250 MOTO-4
Shop parts for a 1990 YAMAHA YFM250 ATV.
This MotoSport-exclusive service guide walks you through safely flushing and bleeding the brake system on a 1990 Yamaha YFM250 MOTO-4. Follow each step carefully, use proper tools and protective gear, and dispose of old fluid responsibly. This procedure covers both front and rear hydraulic brake circuits used on the stock MOTO-4 models.
What you'll need
- Yamaha-specified brake fluid (see notes below) fresh DOT brake fluid only
- Brake bleeder kit (hose & catch bottle) or clear tubing with a calibrated catch bottle
- Wrenches (open-end or flare nut) sized to the bleeder nipples and master cylinder cover
- Phillips screwdriver and small flat screwdriver
- Clean rags, latex or nitrile gloves, and safety glasses
- Brake cleaner and a plastic scraper or nylon brush
- Jack, lift or blocks to stabilize the ATV if you need to remove wheels
- Torque wrench for reassembly (recommended)
Brake fluid type & compatibility
1990 Yamaha YFM250 MOTO-4 models originally used DOT-spec brake fluid. Use fresh DOT 3 or DOT 4 fluid as specified in the Yamaha service literature for your exact MMY. Never mix glycol-based DOT fluid with silicone-based (DOT 5) fluid. If you are unsure, choose DOT 4 for broader compatibility, but confirm with your service manual or MotoSport parts for exact fitment.
Safety & prep
- Work on a level surface with the engine off and key removed.
- Wear gloves and eye protection. Brake fluid damages paint and plastics — cover painted surfaces and immediately clean any spills with water and a rag.
- Keep new fluid sealed until use. Brake fluid is hygroscopic and absorbs moisture if left open.
Pre-bleed inspection
- Inspect brake lines for cracks, swelling or leaks. Replace any damaged hoses before bleeding.
- Check caliper piston seals and master cylinder for weeping. Replace seals or rebuild components that leak.
- Top up the master cylinder reservoir with new fluid so the reservoir never runs dry during the procedure.
Procedure overview
The system should be bled from the wheel furthest from the master cylinder to the closest: on the YFM250 that typically means rear brake first, then front. If the machine has two separate hydraulic circuits (single front caliper & rear), treat each circuit independently. Use a two-person method for the cleanest result or a one-person vacuum/pressure bleeder.
Step-by-step bleeding (two-person method)
- Remove any covers to access the master cylinder reservoir(s) and bleeder nipples. Clean the area thoroughly to prevent contamination.
- Loosen the master cylinder cover screws, remove the diaphragm and cover, then top the reservoir with fresh fluid. Do not overfill; leave room for fluid movement.
- Attach clear tubing to the bleeder nipple on the wheel you will bleed first and place the other end into a catch bottle partially filled with some fresh fluid to prevent sucking air back in.
- Have your helper slowly depress the brake lever/pedal 3-4 times and then hold pressure on the lever/pedal. With pressure applied, open the bleeder nipple about a 1/4 to 1/2 turn to allow fluid and air to escape. Close the nipple before your helper releases the lever/pedal. Repeat until clear fluid with no bubbles flows out.
- Keep the master cylinder reservoir topped between cycles. Never let it run dry.
- Once the fluid runs clear and bubble-free, tighten the bleeder nipple to spec (hand snug plus a small increment, then torque to the recommended value if known), wipe any spilled fluid, and move to the next wheel.
- Repeat the sequence for the remaining wheel(s) working from furthest to closest to the master cylinder.
One-person vacuum or pressure bleeder method
- Connect the vacuum bleeder to the bleeder nipple or attach a pressure bleeder to the master cylinder reservoir per the tool manufacturer's instructions.
- Apply vacuum or pressure to draw fluid from the caliper bleeder nipple until clear, bubble-free fluid appears. Keep the reservoir topped when using a pressure system.
- Proceed wheel-by-wheel from farthest to nearest as above.
Master cylinder rebuild note
If you notice spongy brakes after bleeding, or the master cylinder pushes fluid but pressure fades, the master cylinder seals or caliper seals may be worn. Rebuilding or replacing these components and repeating the bleed is often necessary for a firm pedal/lever feel. Use OEM or quality aftermarket rebuild kits available from MotoSport.
Final checks & road test
- Top off the reservoir to the proper level and reinstall the diaphragm and cover. Tighten cover screws evenly.
- Clean any spilled fluid from painted surfaces with water immediately.
- Firmness check: With the ATV supported, apply the brake lever/pedal several times. Levers should feel firm without excessive travel. If soft, repeat bleeding or inspect for leaks.
- Lower the ATV, perform low-speed braking tests in a safe area to confirm performance. Re-inspect for leaks and re-torque fittings after the test ride.
Model-specific tips for the 1990 YFM250 MOTO-4
- The MOTO-4 can have a small-capacity master cylinder and compact reservoir — it's easy to run the reservoir dry during bleeding, so top frequently.
- Original brake lines age and harden; if hoses are original, consider replacing them with DOT-compliant braided lines or new rubber hoses to restore consistent lever feel.
- Older caliper pistons can corrode or stick; clean and rebuild calipers when you see uneven pad wear or sticking action during tests.
- Reserve extra time for cleaning under the fenders and around the calipers — mud and grime on trail-used MOTO-4s often contaminate the reservoir area if not cleaned first.
- Keep spare master cylinder diaphragms and cover screws handy — they can be brittle on older machines.
Maintenance interval
MotoSport recommends replacing brake fluid at least every two years or sooner if the machine sees heavy use, rode through deep water, or the fluid shows dark discoloration. Regular replacement prevents moisture buildup that causes corrosion and reduced boiling point.
Disposal
Collect old brake fluid in a sealed container and dispose of it at a hazardous-waste facility or auto-parts store that accepts used brake fluid. Do not pour it down drains or onto the ground.
Parts & support
For replacement hoses, caliper rebuild kits, master cylinder parts and recommended fluids tailored to the 1990 YFM250 MOTO-4, check MotoSport parts and tech support to ensure you get correct, model-specific components.
Related Shopping Categories
Shop Brake Fluid for a 1990 YAMAHA YFM250 ATV.
Shop Brake Bleeders for a 1990 YAMAHA YFM250 ATV.
Shop Brake Pads for a 1990 YAMAHA YFM250 ATV.
Shop Brake Lines for a 1990 YAMAHA YFM250 ATV.
Shop Brake Tools for a 1990 YAMAHA YFM250 ATV.
Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle's official owner's manual. Always refer to your manufacturer's documentation for model-specific instructions, torque specifications, safety procedures, and maintenance requirements. If you are unsure or inexperienced, consider seeking assistance from a qualified mechanic or technician.