How to Swap the Fuel Line on a 2000 Yamaha Big Bear 400 2x4
Shop parts for a 2000 Yamaha Bigbear 400 2X4 ATV.
The two-wheel-drive Big Bear 400 traded the front driveline for lighter weight and a lower price, and one small side benefit shows up the moment you start working on the fuel system: with no front differential or front axles crowding the chassis, the hose run between tank and carburetor is easier to see and easier to reach than it is on the 4x4 version. That makes this job about as friendly as fuel work gets.
Carbureted, Which Simplifies Everything
The 2000 Big Bear 400 2x4 is carbureted and gravity fed. A manual petcock at the tank controls the supply, one rubber hose carries fuel down to the carburetor, and the float bowl handles metering. Nothing holds pressure after shutdown and there is no pump inside the tank, so rotating the petcock to off is the only isolation this system needs. A fuel-injected quad would send you looking for the pump fuse, running the engine until it stalls to bleed pressure, and reaching for line-clamping pliers because those machines have no petcock. Your carburetor also has a float bowl drain screw, which is the cleanest way to empty the last of the fuel before any fitting comes apart.
Why Rubber Hose Eventually Gives Out
Two things wear a fuel line out, and they work from opposite surfaces. On the outside, decades of heat cycling drive the plasticizers out of the rubber, hardening the wall until vibration opens fine cracks at each bend. Arid climates speed this up because dry air continuously pulls moisture from the outer skin, which is why hose on a desert machine crumbles years before the same part in humid country.
On the inside, ethanol-blended fuel does the work. Alcohol draws in water, and a line left full through months of inactivity slowly loses its liner to that mixture while leaving gum and varnish behind. The residue narrows the bore and plugs the petcock screen, so a hose can be starving the carburetor while looking entirely acceptable from the outside.
Signs Your Line Is Finished
- A gasoline puddle or damp shadow under the engine after the quad has been parked
- A fuel odor that hangs around the machine even with the petcock closed
- Surface crazing, chalkiness, or a hardened stretch that stays flattened when pinched
- Bogging while pulling a load, hesitation off idle, or lean surging that mimics a dry tank
- A caked ring of dirt at either fitting where fuel has seeped and evaporated repeatedly
The hose ages evenly from end to end, so one failing section is reason to replace the entire run.
Tools, Parts, and Ventilation
- Nitrile or rubber gloves plus eye protection
- An approved fuel container and a wide catch pan
- New line matched to the original inside diameter, cut long and trimmed to fit
- Fresh spring clips or miniature worm-gear clamps
- Screwdriver, needle-nose pliers, razor knife, clear drain tube, and rags
Do the work outside, or with the shop door raised completely. Gasoline vapor is heavier than air, so it sinks and pools in a layer at floor level where an open window several feet up accomplishes nothing, and that is the air you breathe while kneeling next to the machine. Shut down water heater pilots, unplug space heaters, and keep grinders, torches, and cigarettes out of the area entirely. Leave the gloves on the whole time, since raw gasoline defats skin quickly.
Getting the Old Hose Off
Close the petcock, lift the seat, and remove the panels covering the tank outlet and the hose path. Slide the pan into position, then open the float bowl drain screw and route the carburetor's contents into your container through the clear tube. That step captures the majority of the fuel that would otherwise spill.
Back both clamps well clear of the barbs. Old rubber almost always bonds itself to a fitting with dried varnish, so twist the hose to break the seal rather than hauling on it. If it stays locked on, slice it lengthwise with the razor and peel it away in strips instead of prying, because the petcock spigot and the carburetor inlet crack more easily than they look. Note the routing before the last end frees up. Being a 2x4, this Big Bear takes a shorter, more open path than the 4x4 version, without front differential hardware or extra crossmembers to work around, but the original clips still exist for a reason and the new hose belongs in every one of them.
Installation and the Leak Test
Cut the replacement to the same length as the old piece. Extra hose sags into the frame and chafes through, while a short piece pulls sideways on the fittings until one lets go. Seat each end past the raised bead, working the hose on completely dry. Grease, oil, and silicone all belong nowhere near a fuel fitting, since any lubricant film on the sealing surface gives gasoline a path out from under the clamp. A quick dip in hot water softens a stiff end enough to slide on with hand pressure.
Set the new clamps just behind the bead at the petcock and the carburetor, snugging them evenly so the wall is gripped but not crushed. Clip the line into its factory guides, clear of exhaust heat and steering travel.
Close the drain screw and turn the petcock on. Gravity fills the line at once, so watch both joints closely for the first minute. Wipe the fittings dry with a clean rag, inspect them again, then start the engine and idle it for several minutes before a final look under vibration. Since this Big Bear 400 is carbureted rather than injected, its filter screen sits inside the reachable petcock instead of in the tank on a pump module. If the machine still runs lean after a leak-free install, that screen and the carburetor jets are the next things to check.
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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.