Why Your 1968 Honda CL175 Scrambler Is Using More Fuel Than It Used To
Shop parts for a 1968 Honda CL175 - Scrambler Motorcycle.
The 1968 Honda CL175 Scrambler is a small-displacement, air-cooled four-stroke twin with carbureted fuel delivery, a chain final drive, and contact breaker points ignition. That configuration shapes everything about this article. There is no oxygen sensor, no engine control module, and no stored fault codes to interrogate on a bike of this era — the reasons a vintage carbureted machine starts drinking fuel are almost always mechanical, adjustment-related, or simply a matter of how the bike is being ridden. Working through the possibilities from the free checks to the ones that need tools will usually lead you to the answer.
First, Confirm the Change Is Real
Before chasing a mechanical fault, it is worth confirming that fuel economy has genuinely changed. The most reliable method is tank-to-tank measurement: fill the tank to the same level each time, note the odometer reading or reset the trip meter, ride normally, then refill and divide the distance covered by the amount of fuel it took to refill. Do this over several tanks rather than one. A single fill-up can be skewed by how full you managed to get the tank, by a pump that shuts off early, or by one unusually windy or stop-and-go ride. Three or four consecutive tanks give you a trend you can actually trust.
It also helps to remember that the odometer on a bike this old is driven off the drivetrain. A change in rear tire size, or a swap to different sprocket sizes, will make the speedometer and odometer read differently than they used to. If the odometer is now under-reporting distance, your calculated fuel economy will look worse even though nothing about the engine has changed. Riders who never calculate mileage often notice the problem differently — they simply realize they are stopping for fuel more often than they used to on the same familiar routes.
Riding Conditions and Habits That Quietly Cost Fuel
Not every drop in economy is a mechanical problem. Cold weather alone increases fuel consumption, because a cold engine needs a richer mixture to run cleanly, and the CL175 takes a while to reach full operating temperature. Winter-blend and ethanol-blended fuels can also reduce the energy content per gallon, so the same riding produces fewer miles. Headwinds, a passenger, or a loaded set of saddlebags all add drag and weight that a small twin has to overcome with more throttle.
Riding style matters just as much. Aggressive acceleration, holding high rpm, and sustained highway speeds all push a small-displacement engine harder than it was designed to work. Short trips are especially costly, since the bike spends most of the ride in its cold, fuel-rich warm-up phase. Long idling warm-ups before riding fall into the same category: the engine is burning fuel while covering no distance at all. If your routine has changed — a longer commute, more stop-and-go traffic, a new passenger — that alone can explain a noticeable change.
Rolling Resistance: Tires, Brakes, and the Drive Chain
Underinflated tires are one of the most common and most overlooked causes of poor fuel economy. A soft tire has a larger contact patch and deforms more as it rolls, and the engine pays for that extra effort on every revolution. Check pressures when the tires are cold, and check them regularly, since older tube-type tires can lose pressure slowly without any obvious sign.
A dragging brake is the next thing to rule out. On the front, a caliper that is not releasing fully — often from corrosion or a swollen seal — keeps the pads in contact with the rotor. On the rear, a drum brake with a sticky actuating mechanism or an over-adjusted linkage can do the same thing with the shoes. Either way, the bike is fighting itself. After a ride, carefully feel the rotor or drum area; unusual heat on one side points to drag.
Because the CL175 is chain-driven, the chain deserves attention too. A dry, rusty, or overtightened chain robs power and forces you to use more throttle for the same speed. A chain that is correctly lubricated and set with the proper amount of slack spins freely and lets the engine's output reach the rear wheel instead of being lost to friction.
Air Intake and Ignition
An engine needs the right mix of air, fuel, and spark. A dirty or clogged air filter restricts airflow, which upsets that balance and typically pushes the mixture rich. On a bike of this age, the filter element may also be old enough that it has deteriorated or been replaced with something that does not flow as intended. Cleaning or replacing it is inexpensive and often makes an immediate difference.
Spark plugs are the other half of that equation. Worn, fouled, or incorrectly gapped plugs produce a weak or inconsistent spark, so some of the fuel that enters the cylinder never burns completely. That unburned fuel is wasted, and it shows up as sooty deposits on the plug and reduced economy. Because the CL175 uses contact breaker points, ignition timing is another factor. Points wear over time, which changes the timing and can leave the engine running less efficiently than it should. Checking point condition and gap is a reasonable step for a rider comfortable with basic maintenance.
Carburetor and Fuel System Causes
On a carbureted machine, the fuel system itself is a frequent culprit. A choke that is left partially engaged, or a choke mechanism that sticks and does not fully release once the engine warms up, keeps the mixture rich on every ride. This is easy to overlook because the bike may still run acceptably.
Inside the carburetor, a float that is set too high, or a worn needle and seat that no longer seals properly, allows too much fuel into the bowl and produces a rich condition. Jets that have become dirty or gummed up from fuel sitting in the bowl — common on a bike that is ridden seasonally — can also disrupt the mixture. If your CL175's twin-cylinder engine is equipped with more than one carburetor, those units also need to be synchronized; when they are out of balance, one cylinder works harder than the other and overall efficiency suffers.
Finally, look for actual leaks. A weeping petcock, cracked fuel lines, or a seeping float bowl gasket will lose fuel steadily, and the loss is easy to miss because it evaporates rather than pooling on the ground. A persistent fuel smell around the bike is a strong hint.
Engine Condition and Modifications
As any engine accumulates miles, compression tends to drop through ring and valve wear. Lower compression means less of the energy in the fuel is converted into forward motion, so the bike needs more throttle to do the same work. A compression check is the way to confirm this, and it is a job most riders will want a mechanic to perform.
Modifications can also be responsible. Fitting an aftermarket exhaust or a freer-flowing air filter without matching changes to carburetor jetting commonly leaves the engine running rich. If the mileage dropped right after a performance part went on, that timing is a strong clue.
When to Hand It to a Mechanic
Some symptoms point toward a deeper problem than a simple adjustment. A strong, constant fuel smell, black smoke from the exhaust, spark plugs that come out heavily sooted, or rough running alongside the mileage drop all suggest the mixture is significantly off or the engine is not burning fuel properly. If you have checked tire pressure, brake drag, chain condition, the air filter, and the plugs, and the consumption is still high, it is time to bring the bike in. Describe what you have observed — when the change started, how you measured it, and any symptoms you noticed — and a mechanic can dig into the carburetor, ignition timing, and internal engine condition with the right tools.
Related Shopping Categories
Shop Fuel System Parts for a 1968 Honda CL175 - Scrambler Motorcycle.
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Shop Tires for a 1968 Honda CL175 - Scrambler Motorcycle.
Shop Brake Parts for a 1968 Honda CL175 - Scrambler Motorcycle.
Shop Spark Plugs for a 1968 Honda CL175 - Scrambler 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.
