Fuel Line Replacement on a 1987 Yamaha Big Bear 350 4x4
Shop parts for a 1987 Yamaha Bigbear 350 4X4 ATV.
The 1987 Big Bear 350 4x4 arrived as one of the first serious four wheel drive utility quads, and the machines still working today are almost all running fuel hose that is decades past its prime. Fortunately the system is about as simple as fuel delivery gets. This is a carbureted quad with a manual fuel valve under the tank and gravity doing the work, so there is no pump to relieve and no electrical connector to disturb before you begin.
Laying Out the Fuel Path
Fuel leaves the tank through a valve with ON, OFF, and reserve positions. Behind that outlet sits a small strainer screen that traps sediment before it can enter the hose. From there, one length of rubber drops down to the carburetor inlet, held by a clamp at each end and supported partway along by a clip.
Because this is a 4x4 chassis, there is front differential hardware and an extra frame crossmember in the general area, and the hose may take a slightly longer route with one more clearance point than the two wheel drive version of the same platform. The procedure does not change, but the routing is worth photographing before you disturb it. The carburetor also has a float bowl drain screw underneath, and using it is the difference between a clean job and gasoline on your boots.
Why Old Rubber Gives Out
Hose failure is a chemistry problem rather than a wear problem. The plasticizers that keep the rubber flexible slowly migrate out of the material, a process the air cooled engine's heat cycles push along every time you use the machine. Flexible hose becomes hard and shiny, and hard hose cracks at bends and loses its grip on the barbs. In dry, low humidity climates the effect accelerates because the surrounding air draws moisture out of the hose wall.
The inner liner degrades along a separate path. Ethanol blended pump gas pulls water vapor from the air, and that mixture works on the liner during the long stretches a worKing Quad sits parked. The result can be a hose that looks acceptable while its inside surface softens and sheds material toward the carburetor jets. None of this is a flaw in the machine, and on a Big Bear this old the original hose is simply overdue.
Spotting a Bad Line Early
Take any of these as a cue to inspect the hose end to end:
- Fuel pooling under the frame or trailing down the engine after the quad sits with the valve open
- A gasoline smell that lingers in the barn or garage with no spill to account for it
- Hairline cracks, chalky texture, or a stiff section you can feel through a glove
- Bogging as the throttle opens, lean surging at cruise, or the engine quitting like the tank went dry
- Dust caked residue rings at the fittings where seeping fuel dried in place
The running symptoms usually beat the visible leak, because a small crack lets the hose draw air rather than push fuel out. Lean running heats an air cooled engine, so do not put this off once the machine starts complaining.
The Kit for This Job
Set all of this out before the valve gets closed:
- Gasoline rated hose sized to the original inside diameter
- New clamps, since original spring clips lose tension and old worm gear clamps seize
- Gloves and eye protection
- A drain pan and a sealed container approved for fuel
- Screwdriver, pliers, a fresh utility blade, and rags
- Hand tools for the seat and side cover
Handle the gasoline properly. Its vapor is heavier than air, so it sinks and spreads across the floor toward pilot lights, heaters, and electrical connections down at ground level. Work outdoors, or open the shop door completely and run a fan low, moving air away from the machine. Shut down anything with a standing flame, avoid hot bulb work lights, keep an extinguisher within reach, and let fuel soaked rags dry outside rather than sealing them in a can.
Disconnecting Both Ends
Turn the valve to OFF, then remove the seat and any panel that blocks your view. Slide the pan under the carburetor and open the float bowl drain screw, letting the bowl empty before you touch a connection.
Push both clamps well back along the hose. Fuel varnish bonds old rubber to brass, so break that seal with a gentle quarter turn at the barb, then draw the hose off with steady pressure and a rag ready to catch the trickle. If an end refuses to release, split the hose lengthwise with the utility knife and peel it away in two pieces instead of prying, which is what cracks fittings on a machine this age. Free the valve end the same way, and as the old hose works its way past the front driveline area, note every clip and clearance point it passes.
Seating the Replacement and Sealing It
Cut the new hose to the length of the piece you removed. Extra hose sags toward moving parts and eventually chafes through, while a short piece keeps both barbs under tension whenever the engine rocks. Push each end fully onto its fitting until it bottoms out, working dry. Grease, oil, and silicone all create a leak path along the barb and add nothing to the grip, so keep every lubricant away from the fittings. Dip a stiff hose end in hot water for a few seconds if it resists.
Position the clamps just behind the raised bead on each fitting and tighten evenly until the hose stops rotating. That is enough torque. Crushing new hose with a worm gear clamp slices the wall and produces the next weep. Route the finished line back through its original clip, clear of the exhaust, the engine cases, and the front drive hardware.
Checking Your Work
Open the valve and wait a minute before starting. Gravity refills the carburetor bowl during that time, giving you a cool, quiet window in which any seep is obvious. Wipe both joints with a dry rag, pause, then look for fresh fuel. Once they hold, start the engine and let it idle to operating temperature, checking again with the chassis vibrating.
Ride a slow lap, shut down, and inspect both fittings once more before the bodywork returns. While the area is open, rinse the strainer screen at the valve outlet and make sure the tank vent breathes. A blocked screen or vent starves the carburetor exactly the way a failing hose does, and clearing both now keeps the new line from taking the blame.
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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.