Fuel Line Service on the 1987 Yamaha YFM350ER Moto–4

Shop parts for a 1987 Yamaha YFM350ER MOTO-4 ATV.

The YFM350ER was the big–bore Moto–4, and the 1987 model still earns its keep hauling firewood and checking fence lines. Its fuel system is completely mechanical: a carburetor handles mixture, a manual petcock threaded into the underside of the tank shuts flow off with a lever, and one rubber hose lets gravity do the delivery. Nothing in the circuit is pressurized and there is no pump to disable, so the whole job comes down to hose, clamps, and careful handling of gasoline.

Why This Hose Has an Expiration Date

Fuel hose deteriorates from the outside and the inside at once. Externally, plasticizers leach out of the rubber under heat cycling, and the 348cc air–cooled cylinder on this Moto–4 makes plenty of heat right next to the line. Season after season the compound turns stiffer, and eventually it cracks where it used to flex. Owners in arid regions hit that point sooner, because dry air pulls moisture out of the hose wall and leaves the rubber hard and glassy.

Internally, ethanol–blended pump gasoline is the aggressor. The alcohol in E10 draws in water vapor and holds it, and that mixture is considerably harder on mid–1980s rubber than the fuel the 350ER was engineered for. When the machine sits for months with fuel still in the line, gum and varnish build in the passage while the liner softens. The failure begins where you cannot see it, which is exactly why a hose that looks fine can still be shedding debris downstream.

Symptoms on a Machine This Size

The 350 pulls hard enough to expose a fuel restriction that a smaller engine might tolerate. If the line has narrowed or is collapsing internally, the float bowl cannot keep up with demand, so the quad will idle fine and then bog under load, surge lean while lugging in a tall gear, or stall part way up a long grade as though the tank ran dry.

Alongside that, look and smell for the classic signs: raw gasoline odor hanging around the machine after shutdown, a damp ring or drip on the floor under the engine cases, visible checking along the hose, a section that feels rigid when pinched, and a dust–caked collar at either clamp where seeping fuel has trapped grime and evaporated.

Assembling Tools and Prepping the Area

  • Correctly sized fuel hose for the YFM350ER, bought long so you can trim to match
  • Two fresh clamps in the factory style rather than the fatigued originals
  • Nitrile or rubber gloves plus safety glasses
  • A metal or fuel–rated container and a stub of scrap hose to aim the drain
  • Flat–blade screwdriver, sockets for the seat and panel hardware, a sharp razor knife
  • Plenty of clean rags and a dry chemical extinguisher staged nearby

Take the fuel handling seriously. Gasoline vapor is heavier than air, so it does not waft out an open window. It spills across the floor and settles into low corners where a water heater pilot flame, a shop heater, or a battery charger sitting on concrete can ignite it. Work outdoors when possible. If you must be inside, open the door fully and leave it open for the duration, shut off every pilot and heat source in the space, and keep gloves on so raw fuel is not stripping the oils out of your skin.

Removing the Old Line

Turn the petcock to OFF. That lever is the advantage of a carbureted quad; a fuel injected model would have no petcock at all and you would be pulling a pump fuse and pinching the hose shut with line clamping pliers instead. Take the seat off and loosen whatever panel is between you and the carburetor inlet.

Drain what is left downstream by slipping the scrap hose onto the float bowl drain nipple, routing it into your container, and cracking the drain screw at the base of the carburetor. Close it when the flow stops. Slide both clamps well back from the barbs, put a rag beneath the joint, and twist the hose on the spigot to shear the varnish bond before applying any pull. An end that stays stubborn should be split lengthwise with the razor and peeled away rather than levered, since a forty year old petcock spigot and carburetor inlet both break with very little provocation.

Trace the routing as the old hose comes out and note each guide and clip. The 350ER is a two–wheel–drive machine with no front differential in the way, so the run stays short and reachable, unlike the longer path a 4x4 utility quad forces around front driveline hardware.

Fitting the Replacement and Proving It Dry

Trim the new hose to match the original exactly. Extra length drapes toward the exhaust or loops into the frame, and a short piece leaves both fittings under standing tension. Press each end onto its barb dry until it bottoms against the shoulder, softening a tight end with a quick dip in hot water. Keep grease, oil, and silicone completely off the fittings. A lubricated sealing surface gives gasoline a channel to travel under the clamp, and that shortcut is behind a great many leaks on brand new hose.

Set each clamp just behind the raised bead on its spigot and tighten firmly without crushing the rubber. Return the hose to the original guides so it clears hot surfaces and does not tug at full steering lock.

Now switch the petcock to ON and simply watch for several minutes. Gravity puts static pressure on both joints right away, so a bad connection shows itself before the engine has even turned over. Blot each fitting with a clean light–colored rag so a slow weep leaves a visible mark rather than hiding on dark rubber. Start the engine next, let it idle a few minutes, and inspect both ends again with the motor vibrating, since that is what exposes a marginally tight clamp.

Finish by backing the petcock out and rinsing its strainer screen in clean fuel. All the rubber crumbs and sediment the failing hose sent downstream collected there, and on this 350ER that screen plus the float bowl is the entire filtration system. A clean screen behind a fresh line puts fuel delivery back where it belongs.

Related Shopping Categories

Shop Fuel Lines for a 1987 Yamaha YFM350ER MOTO-4 ATV.

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Shop Petcocks for a 1987 Yamaha YFM350ER MOTO-4 ATV.

Shop Fuel Filters for a 1987 Yamaha YFM350ER MOTO-4 ATV.

Shop Fuel Stabilizer for a 1987 Yamaha YFM350ER MOTO-4 ATV.

Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your ATV'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.