Why does a motorcycle shake when starting?

[DePaisley]

Motorcycle shaking during startup is caused by poor contact of the rear clutch or friction powder on the surface of the shoe blocks, which reduces the friction between the shoe blocks and the housing, resulting in slipping. A motorcycle is a two- or three-wheeled vehicle driven by a gasoline engine, steered by handlebars to control the front wheel. It is lightweight, flexible, fast-moving, and widely used for patrol, passenger and cargo transportation, as well as a sports equipment. Broadly speaking, motorcycles are divided into street bikes, road racing motorcycles, off-road motorcycles, cruisers, and touring bikes. A motorcycle consists of five main parts: the engine, transmission system, running gear, braking system, and electrical instrumentation equipment. The transmission system of a motorcycle includes primary reduction, clutch, gearbox, and secondary reduction components.

[VonAlexander]

Last time my motorcycle also shook when starting, and the problem was traced to the clutch. The clutch plates on the old bike were severely worn, causing severe slippage and shaking during takeoff. A loose chain is another common cause—if the rear section of the chain wobbles enough to fit three fingers in, it will rattle loudly when starting. If the spark plugs are overdue for replacement, the engine may also struggle and shake. I suggest first tightening the chain—the standard is no more than 3 cm of vertical play. If it still shakes after adjustment, chances are you’ll need to open it up and check the clutch plates. Remember to regularly spray some lubricant on the chain and add oil to the clutch cable every six months to prevent small issues from turning into big troubles.

[LouisAnn]

As a seasoned rider with over a decade of motorcycle experience, I've found that startup vibrations are mostly caused by inadequate maintenance. A loose chain can make the entire rear drive system dance, while a dry and sticky clutch cable can make the clutch release feel rough—these two are the most common culprits for startup vibrations. If the fuel filter is clogged, the bike might shake like it's got the chills during sudden acceleration due to insufficient fuel supply. Before every ride, I make it a habit to kick the rear wheel a couple of times to check the chain tension and ensure the clutch cable moves smoothly. If the handlebars start shaking too, it's definitely a sign that the engine mount bolts have loosened. Regular checks are the key to keeping your old steed running smoothly.

[LoganDella]

My 125cc scooter has been shaking a lot during startup recently. After disassembling it for inspection, I found three issues. The clutch friction plates were worn as thin as paper, and the flywheel on the engine side had grooves worn into it. The grease on the rear axle had long since dried up, and the bearing balls were rusted and stuck. The most serious issue was the carburetor's incorrect air-fuel mixture, with the spark plug covered in carbon deposits as black as coal. After replacing the clutch assembly myself, applying high-temperature grease to the rear axle, and recalibrating the carburetor, it instantly became much smoother. Actually, the shaking was caused by small parts gradually wearing out—key components should be inspected and maintained every 5,000 kilometers.