Why Your 1991 Suzuki VX800 Is Using More Fuel Than It Used To
Shop parts for a 1991 Suzuki VX800 Motorcycle.
The VX800 is a liquid-cooled, four-stroke V-twin with carbureted fuel delivery and a chain final drive. That configuration shapes everything below. Because this bike feeds fuel through carburetors rather than fuel injection, there is no oxygen sensor trimming the mixture and no computer compensating for changing conditions — the air/fuel ratio is set mechanically, and anything that disturbs that balance shows up as extra fuel burned. The good news is that most causes of a sudden drop in fuel economy on a machine like this are findable without dealer-level diagnostic equipment.
First, Make Sure the Change Is Real
Before chasing a mechanical cause, measure. Fill the tank, reset the trip meter or write down the odometer reading, ride normally for the whole tank, then refill at the same pump and note how much fuel went in. Divide the miles ridden by the fuel added. One tank proves very little — wind, temperature, and how you rode all move the number. Track three or four consecutive tanks and look at the trend instead.
Also consider whether the odometer is telling the truth. A change in rear tire size, or a sprocket change on this chain-driven bike, alters the relationship between actual distance traveled and what the odometer records. If the odometer now reads high, your calculated economy looks worse than reality. Riders who never calculate anything usually notice the problem differently: more frequent fuel stops, or fewer miles between fill-ups than the bike used to deliver.
Riding Conditions and Habits That Quietly Cost Fuel
Not every drop in economy is a fault. Cold weather thickens oil, lengthens warm-up, and increases rolling resistance, and many areas switch to a winter fuel blend that simply contains less energy per gallon. Ethanol-blended fuel has a similar effect. A steady headwind, a long stretch of sustained highway speed, or a passenger and loaded luggage all demand more throttle for the same distance.
Riding style matters just as much. Hard acceleration, late braking, and holding high rpm in a lower gear than necessary all burn fuel that a smoother approach would save. Very short trips are especially costly, because the engine spends most of the ride warming up and running rich. Long idling warm-ups in the driveway do the same thing while covering zero miles.
Rolling Resistance, Brakes, and the Drive Chain
Start with tire pressure. Underinflated tires are the most common and most easily corrected cause of poor fuel economy, and they also wear faster and handle worse. Check both tires cold with a reliable gauge and bring them to the pressure appropriate for your load.
Next, check for drag. A brake caliper that is not fully releasing, or a rear drum brake adjusted too tight, keeps the bike working against itself. After a ride, carefully feel the brake discs and the rear drum area — a wheel noticeably hotter than the others points to a dragging brake. On the VX800's chain drive, a dry, rusty, or overtightened chain soaks up power and fuel. Clean and lubricate it, and set the slack to spec.
Air Intake and Ignition Health
A clogged air filter restricts airflow and richens the mixture, which costs fuel. Inspect the filter and clean or replace it as its type allows. Spark plugs matter too: worn, fouled, or incorrectly gapped plugs produce incomplete combustion, so some of the fuel you paid for leaves unburned. Pull the plugs and read them — dark, sooty deposits suggest a rich condition worth investigating further.
The VX800 uses electronic ignition, so there are no contact breaker points to wear or gap, and timing drift from point wear is not a factor here. If the ignition system is suspect, the practical checks are plug condition, plug cap and wire condition, and battery voltage.
Carburetor Problems That Cause a Rich Condition
On a carbureted V-twin, the fuel system is where a genuine rich-running problem most often lives. A choke or enrichener circuit that sticks partially open is a classic culprit — the engine runs acceptably but drinks fuel. Confirm the choke mechanism returns fully and that the cable is not holding it partly engaged.
Inside the carburetors, a float level set too high, a sticking float, or a worn needle and seat lets more fuel into the mixture than the engine needs. Jets that are dirty or gummed up from a bike that sat unused can also disrupt metering. Because the VX800 is a multi-cylinder machine with a carburetor per cylinder, synchronization matters: carburetors that are out of sync make the engine run unevenly and less efficiently. Finally, look for leaks — a weeping fuel line, a seeping float bowl gasket, or a petcock that drips. A leak may not change combustion, but it absolutely changes how often you refuel.
Engine Condition, Cooling, and Modifications
Low compression from general engine wear reduces efficiency across the board, and a compression check is the way to confirm it. Because the VX800 is liquid-cooled, a thermostat stuck open is also worth considering. An engine that never reaches full operating temperature runs richer than it should and burns more fuel, and the behavior of the cooling system can hint at it.
Modifications deserve a mention. An aftermarket exhaust or a high-flow air filter installed without matching carburetor jetting can leave the mixture poorly matched, and a setup that ends up rich is also thirsty. If the mileage dropped right after a change, that change is the first place to look.
When to Hand the Bike to a Mechanic
Some symptoms point past basic maintenance. A strong fuel smell, black exhaust smoke, sooty spark plugs, rough running alongside the mileage drop, or a warning light on the dash if your bike has one all suggest a deeper fueling or ignition problem. So does a fuel economy drop that persists after you have corrected tire pressure, chain condition, air filter, and plugs.
When you bring the VX800 in, describe what you have measured and what you have already checked. Telling a mechanic that the bike is carbureted, that you have tracked several tanks, and that the drop came on gradually or suddenly gives them a real head start — and usually a shorter path to the fix.
Related Shopping Categories
Shop Fuel System Parts for a 1991 Suzuki VX800 Motorcycle.
Shop Air Filters for a 1991 Suzuki VX800 Motorcycle.
Shop Tires for a 1991 Suzuki VX800 Motorcycle.
Shop Brake Parts for a 1991 Suzuki VX800 Motorcycle.
Shop Spark Plugs for a 1991 Suzuki VX800 Motorcycle.
Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle'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.
