Why does my Yamaha XL800 rev loudly but not accelerate?
I have a 2000 Yamaha XL800 2-stroke. When I open the throttle, the engine revs up really loudly, but there is absolutely no acceleration or drive. It feels exactly like a slipping clutch on a manual car. What should I check first?
Answer
If your Yamaha XL800 engine revs freely but the hull does not accelerate, you have a loss of thrust in the jet pump system known as cavitation. Debris blocking the intake grate, a damaged impeller or excessive clearance between the impeller and the wear ring causes this failure.
Intake Grate Blockages
Rule out a physical blockage before dismantling the pump. Disconnect the battery negative lead before putting hands near the intake grate or impeller. A plastic bag, seaweed or stray tow rope sucked against the intake grate starves the pump of water. The impeller spins in an air pocket. The engine over-revs instantly while producing zero forward thrust.
Put the ski on a trailer or lift. Get underneath with a torch and look up through the intake grate. Check the entire intake tract back to the leading edges of the impeller. A small piece of debris caught on the impeller blades or stator vanes disrupts water flow enough to cause severe cavitation. If debris wraps tightly around the driveshaft, remove the intake grate (held by four 12mm or 14mm bolts) and cut the obstruction away with a utility knife.
Measuring Wear Ring Clearance
If the intake is clear, check the wear ring. The XL800 uses a 155mm jet pump with a stainless steel liner surrounding the impeller. Sand and small stones grind away the impeller edges and this liner. When the gap becomes too large, high-pressure water escapes past the blade tips instead of exiting the steering nozzle. The pump slips.
Check this without removing the pump. Look up through the intake grate. Use long feeler gauges to measure the gap between the edge of the impeller blades and the wear ring.
- Standard clearance: 0.35mm to 0.45mm.
- Service limit: 0.60mm.
If the gap exceeds 0.60mm anywhere around the circumference, remove the pump. Replace the wear ring housing (aftermarket options from WSM or SBT cost £40 to £60). Replace the impeller if the blades show heavy wear.
Impeller and Stripped Splines
Inspect the leading edges of the impeller blades. If rock strikes leave them chipped or bent, the impeller cannot bite the water efficiently. A damaged impeller requires refurbishment or replacement. A Solas Concord impeller (such as the YF-CD series) serves as the standard aftermarket upgrade for the XL800 and costs roughly £250.