Hijet S110P — Diagnostic Protocols

Carburetor tuning, EVAP canister flooding, and vacuum-actuated 4WD troubleshooting.

Carburetor Adjustment & Rebuild

The EF-NS uses an Aisan/Mikuni-style carburetor. Rebuild kits are available for carburetors 21100-87702, 21100-87710, and 21100-87729.

Tip:After a full rebuild, lightly seat the mixture screw — do not overtighten or you will score the brass tip — then back it out exactly 2.5 turns. This is the starting baseline. Once the engine is fully warm and the automatic choke has opened completely, adjust the idle speed screw to 950 RPM.

Lean vs. Rich Diagnosis

Condition	Symptoms	Plug Appearance
Lean	Weak, fluctuating idle — spitting or stumbling under acceleration	White or very light gray porcelain
Rich	Black sooty exhaust — stumbling off idle — poor fuel economy	Black, carbon-fouled

Target exhaust readings: CO 1.5% (+1.0% / −0.5%) and HC below 900 PPM.

Warning:If the catalytic converter temperature warning light (the “barbecue light”) illuminates, the engine is running rich and dumping raw fuel into the exhaust. Fix the mixture or repair the automatic choke — the converter substrate is at risk of overheating. Do not tape over the light.

EVAP Canister Flooding

Topping off the fuel tank after the pump nozzle clicks off is the single most common cause of a flooded canister. Raw liquid fuel gets forced past the expansion valves and into the charcoal canister, which physically blocks tank venting.

Symptoms

Strong fuel smell around the vehicle
Pump nozzle clicks off after filling only ~1 gallon
Pressurized hiss when the fuel cap is removed
Rich running, stalling, or no-start after fueling

What Happens

A saturated canister cannot vent the tank. Pressure builds until the mechanical fuel pump delivery pressure spikes — that excess pressure forces the carburetor float needle off its seat, flooding the intake manifold with raw fuel. The engine will run extremely rich, stall, or refuse to start.

Note:Replace the charcoal canister (OEM 77704-97501) and verify the tank rollover valve is functional. A saturated canister cannot be dried out — the activated carbon is permanently contaminated once liquid fuel soaks it.

Vacuum-Actuated 4WD System

The S110P engages the front differential via engine vacuum routed through electromagnetic solenoid valves (VSVs) to a diaphragm actuator on the differential. The factory service manual notes that 99% of 4WD engagement failures are a vacuum leak — not a mechanical gear failure.

The VSV array is color-coded: a brown solenoid and a blue or gray solenoid control routing to the actuator.

Actuator Test

Use a hand-held vacuum pump (Mityvac or equivalent) to isolate the actuator before condemning anything else:

Disconnect the vacuum line at the actuator and connect the pump directly to the actuator port.
Draw vacuum to 450 mmHg. The actuator arm should move inward (toward the left) — you will hear and feel it move.
Hold the vacuum for 20 – 30 seconds and watch the gauge.
If pressure drops below 450 mmHg in less than 15 seconds, the internal diaphragm is ruptured — replace the actuator unit.
If the actuator holds vacuum, the fault is upstream: check the vacuum hoses for dry rot or cracks, the check valve for blockages, and the VSV solenoids for continuity.

Danger:Never spray carburetor cleaner into the vacuum lines or actuator port. The solvents will immediately dissolve the rubber check valves and the actuator diaphragm, causing total and irreversible 4WD system failure.