Ski Doo MXZ 2000 Carbonator Repair and Wiring Diagram Guide
Begin troubleshooting by securing the official service manual for the 1999–2001 performance sled series–specifically the variant equipped with the high-performance power valve assembly. Locate section 6C (Induction & Fuel Delivery) and reference illustration plates 6-12 through 6-15, which detail injector positioning, throttle body linkages, and pressure regulator connections. Without these visuals, critical inline filters between the main fuel rail and pressure damper unit may be overlooked, leading to incorrect vacuum readings or fuel starvation at midrange RPMs.
Trace the low-pressure fuel line from the pump outlet to the regulator input, noting the in-line fuel temperature sensor (typically mounted near the left cylinder bank). Verify continuity across its terminals–resistance values should drop below 200 ohms at -10°C or rise above 1 kΩ at 50°C. A malfunctioning sensor skews ECU fuel trim, mimicking a lean condition under load. Replace if readings deviate by more than 15% from manufacturer specs (Bombardier service bulletin #SB-2000-03).
Disassemble the vapor separator canister (under the seat cowl) and inspect the internal mesh filter–carbon buildup exceeding 2mm restricts return flow, causing hesitation on cold starts. Clean with non-residue brake cleaner and compressed air at 30 PSI, directing flow opposite the normal fuel path. Recheck the O-ring seal (part #501887301)–degradation here produces vacuum leaks, falsely tripping the fault code P0230 for fuel pump circuit issues.
For precise wire routing, refer to the wiring harness overlay (section 8A of the manual). The MAP sensor connector (Gray 2-pin) must align with the 4.8mm black/white stripe lead; cross-wiring causes erratic ignition timing. Use a pinout tester (Fluke 983 or equivalent) to confirm signal voltage between 0.5V (idle) and 4.5V (wide-open throttle). Readings outside this range indicate either a clogged vacuum line (check for kinks near the intake manifold) or a failing sensor–replacement cost averages $87 USD, excluding labor.
When reassembling, torque the throttle plate screws to 3 Nm–over-tightening distorts the bore, creating airflow irregularities detectable by a butterfly plate drag test. Apply Loctite 243 to the threads of the pressure regulator bolts (M8x1.25) to prevent vibration-induced loosening, which leads to fuel pressure spikes above 45 PSI at high RPMs.
Technical Blueprint for the 2000 Model Snowmobile Fuel System
First, locate the float chamber on the left side of the carburetor assembly–marked by a brass drain screw. This component regulates fuel delivery via dual 38mm throttle bores, each fed by independent jets sized 150 (main) and 45 (pilot). Verify float height at 14.5mm ±0.5mm using a precision gauge; incorrect settings cause flooding or lean burn.
Disconnect the primer hose before servicing–the pump cycles 0.3cc per stroke under 6 psi, referenced in section 4B of the OEM service manual. Replace cracked hoses immediately; they degrade rapidly under -20°C operating conditions, risking vacuum leaks that trigger erratic idle at 1,200 RPM.
Inspect the choke plate for warping; a deviation exceeding 0.1mm disrupts airflow ratios, evidenced by cold-start failures requiring excessive cranking. The plate pivots on a stainless steel shaft lubricated with molybdenum grease–apply sparingly to avoid gumming during thermal expansion.
The accelerator pump diaphragm should hold 5 inches of vacuum for 10 seconds without leakage–test with a handheld gauge. Failure here manifests as hesitation during aggressive throttle input below 4,000 RPM, traced to deteriorated viton seals.
Rejet the main circuit with a 160 jet for elevation above 1,500 meters–lean conditions starve the cylinder, causing piston scuffing visible as dark streaks on the skirt. Use a bore scope to confirm cleanliness of the idle passage; debris as small as 0.2mm obstructs fuel flow.
Adjust the air screw precisely 1.5 turns out from seated; each quarter-turn alters A/F ratio by 5%. Record baseline readings at sea level for reference–altitude compensation requires recalibration every 300 meters gain.
Secure electrical connections on the solenoid with dielectric grease; corrosion induces premature activation of the enrichment valve, dumping raw fuel into the intake tract. Replace the OEM solenoid if resistance exceeds 12 ohms–verified with a multimeter in continuity mode.
Finding the Fuel Mixer Unit in the Rotax 503 Powerplant Compartment
Begin by removing the seat and left-side fairing panel–secured with four Torx T25 bolts and two quick-release clips near the hinge. The fuel mixer assembly sits directly beneath the airbox, mounted to the cylinder head via three M8 studs; follow the intake runners from the reed valve block upward to identify its position. A 12 mm wrench will loosen the mounting nuts, but ensure the throttle cable bracket is detached first to avoid tension damage.
Trace the vacuum hose from the pump diaphragm nipple–it connects to a single brass barb on the rear of the mixer’s body. This reference point eliminates confusion with the adjacent idle speed solenoid or MAP sensor ports. If corrosion obscures the brass fitting, rotate the flywheel counterclockwise until piston #1 reaches TDC; the mixer’s positioning mark aligns with the timing pointer on the stator plate.
Key Reference Points for Rapid Identification
- Intake boot: Large black silicone tube sandwiched between reed block and mixer–separates at the lower clamp.
- Choke linkage: Grey plastic lever on the right side, connected by a ball joint rod.
- Ground strap: Single 8 AWG wire terminating in a ring lug under the right-rear mounting stud.
- Fuel inlet: 6 mm banjo bolt with crush washer, color-coded with green tape.
- Drain plug: 1/4″ NPT fitting at the bottom of the float bowl–requires a hexagonal key for access.
Leverage a flexible inspection mirror to examine the rear of the unit; the brass fuel return nipple (3 mm OD) sits adjacent to the electrical connector for the pump dwell circuit–confirmed by a white/violet tracer wire. Misidentification risks stripping threads on the float bowl screws, which are torqued to 5 Nm.
Step-by-Step Guide to Disassembling the Fuel Mixing Module for Cleaning
Begin by relieving fuel pressure: disconnect the battery’s negative terminal and press the electric start for 3 seconds to drain residual pressure. Failure to do this risks fuel spray exposure, which can ignite or damage seals. Wear nitrile gloves and safety goggles throughout.
Remove the airbox assembly (8 Torx T25 screws) to expose the mixing unit. Label each hose with masking tape–note positions for the crankcase breather (11mm diameter), primer line (6mm), and overflow (4mm). Disconnect the throttle cable by rotating the barrel adjuster counterclockwise until slack allows the cable end to slide free from the cam. Store screws and components in magnetized trays to prevent loss.
| Component | Fastener Type | Quantity | Torque (Nm) |
|---|---|---|---|
| Airbox bolts | Torx T25 | 8 | 4.5 |
| Body mounting screws | Phillips #2 | 6 | 3.2 |
| Diaphragm cover | Slotted 5.5mm | 4 | 2.8 |
Unbolt the module’s body (6 Phillips #2 screws) using a calibrated screwdriver set to 3.2 Nm. Separate the upper and lower housings carefully–pry points are molded near the gasket flanges. Lift the diaphragm assembly vertically to avoid tearing the 0.15mm nitrile membrane. Inspect the mesh filter beneath it; if clogged with varnish (>50% coverage), soak it in acetone for 10 minutes and agitate with a nylon brush.
Flush the fuel passages with 150psi compressed air. Insert the nozzle into the inlet port and pulse air in 2-second bursts to dislodge debris without damaging check valves. Verify valve movement by blowing through the outlet while blocking alternate ports–resistance should reverse with each breath. Replace O-rings if compression set exceeds 20% (measure with calipers). Lubricate new seals with Molykote 55M before reinstallation.
Reassemble in reverse order, torqueing fasteners in a cross-pattern to 80% of spec first, then 100%. Reconnect hoses according to labels–primer line (white stripe) must align with the marked barb. Reattach the throttle cable with 2mm free play at wide-open position. Pressure-test by priming until fuel drips steadily from the overflow (max 10 seconds).
Critical Engine Fueling System Elements and Wiring Layout
Trace the primary fuel pump relay first–locate it adjacent to the voltage regulator on the right chassis rail. Its 4-pin connector interfaces with terminal 87a (common) and 30 (supply), while terminals 85 (trigger) and 86 (ground) link directly to the ECU. Verify the relay coil resistance between 85 and 86; readings outside 70–90 ohms indicate coil fatigue requiring immediate replacement to prevent intermittent fuel starvation.
Examine the throttle position sensor (TPS) wiring harness for strain relief at connector C3. The three wires–5V reference (red), signal (yellow), and ground (black)–must maintain uninterrupted contact. Probe the signal wire with a multimeter set to DC voltage; readings should sweep from 0.5V (closed) to 4.5V (wide open) without voltage drops exceeding 0.1V. Secure the TPS mounting screws to 3 Nm torque to eliminate sensor drift caused by vibration.
Injection System Interconnections
- Fuel Injectors: Each injector pair shares a single power feed from the fuel pump relay, daisy-chained via 16-gauge red wires. Tap into the circuit at the first injector’s positive terminal to measure voltage drop under load; anything above 0.3V suggests corroded terminals or undersized wiring requiring crimped ring terminals.
- Injector Ground: All six injectors converge at a single ground bus bar bolted to the engine block. Scrape the block’s mating surface to bare metal and apply dielectric grease before reconnecting; resistance above 0.5 ohms between the bus bar and chassis ground triggers erratic fueling.
- Pulse-Width Modulation: The ECU modulates injector duration via a 12V square wave on the green/white striped wire. Connect an oscilloscope to confirm a clean signal with rise/fall times under 5 microseconds–any distortion implies ECU output transistor failure.
Inspect the manifold absolute pressure (MAP) sensor’s vacuum line for cracks. The nylon tubing should flex smoothly when routed behind the cylinder head; replace if brittle. At connector C2, the MAP sensor’s 5V reference (orange), signal (green), and ground (black) wires must resist moisture ingress–seal with silicone dielectric if terminals show oxidation. Monitor MAP signal voltage at idle (1.2–1.8V) and snap throttle (3.5–4.2V); deviations outside this range point to intake leaks or sensor calibration drift.
Ignition and Auxiliary Circuits
Follow the ignition coil wiring from the CDI module. The twin 10-gauge red wires supply battery voltage, while the black/white striped wires carry control signals. Check for voltage drop across the coil power feed; readings above 0.2V mandate bypassing the stock fuse block with a 30A relay. Replace the coil’s rubber isolation boots if cracked–even minor insulation breakdown causes misfire codes P0301–P0303.
- Disconnect the battery negative terminal before servicing the CDI module’s 5-pin connector. Corrosion on pins 1 (trigger) and 3 (ground) disrupts timing synchronization, yielding rough idle.
- Reinstall connectors with anti-seize compound on threads; torque to 6 Nm to prevent vibration-induced looseness.
- Validate timing advance with a strobe light–base setting should be 8° BTDC at 1,000 RPM with no load; ECU trim adjusts this dynamically at pin 2 via a 0–5V feedback loop.
Inspect the O2 sensor’s yellow/black wire for chafing near the exhaust manifold. Probe heater resistance (4–8 ohms); failure here triggers fuel trim faults. Replace the sensor if voltage response during warm-up exceeds 0.3V/s slope–sluggish response leads to AFR readings exceeding 15:1.