MotoMojo Motorcycle Malfunctions: What to Do When Your Bike Quits or Won’t Start

Apr 07, 2012 View Comments by

Motorcycles have become very reliable, but occasionally problems still happen. If the engine stalls on the road, get to a safe place. If it’s losing oil pressure or overheating, stop immediately. Engines need compression, gas, and spark to run; you must determine which is lacking. Most stalls and no-starts are caused by minor problems like fuel starvation, a discharged battery, or a bad connection. Here are some checks you can do on the side of the road.

Starter
Make sure the clutch is in, sidestand up, petcock on, and kill switch in the run position. Also, check if the choke (if equipped) is in the proper position. If it seems like an electrical failure, wiggle the ignition switch. If the starter sounds normal, your problem is likely fuel- or spark-related. If the starter won’t spin, you may have a discharged battery or bad starter, solenoid, or connections.

If all the lights dim or go completely out when you press the starter button, the battery is likely discharged. (Some bikes shut the headlight off when the starter is activated; if so, check taillight brightness.) Before condemning the battery, clean and tighten the terminals.

If the battery checks out OK but the starter doesn’t work, look for a blown fuse or a malfunction in the sidestand switch, clutch-lever switch, or gearshift interlock switch. If a switch is bad, it may be possible to temporarily bypass it. If a fuse is blown, replace it. If it blows again, there’s a short somewhere that needs to be repaired. If the bike has been wet, water may be in the ignition switch, spark plug caps, kill switch, or sidestand switch. You may be able to remove it with WD-40 or other water dispersants.

Bikes with a low battery (and no kicker) can be jump-started with booster cables (observe safety instructions) and sometimes push-started. With the ignition and fuel petcock on, place the bike in second gear, hold in the clutch, and get the bike up to about 10 mph. Quickly release the clutch lever, and the engine should spin over fast enough to start.

Fuel
Remove the gas cap and look inside the tank for fuel level and possible contamination with a flashlight or sunlight. If the bike has a manual fuel petcock, turn it to reserve; with a vacuum-operated petcock, turn it to prime. With a cool engine and away from any ignition sources, you can check for fuel at a carburetor by unscrewing a float-bowl drain screw. (Do not try this with EFI, as high pressure will spray fuel.) Catch the gas in a clear water bottle to see if it contains water or dirt. If no fuel flows, gas may not be getting through a petcock, or there may be a clogged fuel filter. To check on carbureted models, remove the gas hose at the petcock and turn it to reserve. If gas flows out, but doesn’t reach the carburetor float bowl (drain screw open), the problem is most likely a clogged fuel filter. Sometimes you can temporarily clear a filter by blowing backward through it.

Fuel-injected engines have in-tank electric fuel pumps, which are a common cause of no-starts. Typically, the pump runs for a few seconds when the ignition is turned on. Listen for the pump by holding your ear to the tank. Some pumps only operate when the engine is cranking or running, so if the pump doesn’t run when the ignition is turned on, operate the starter for a few seconds and listen. If the pump doesn’t work, the pump or its circuitry may have failed; check the fuse and electrical connections. As with carbureted engines, if the pump runs but gas isn’t getting to the engine, the filter may be clogged.

Checking Spark
If the engine cranks but won’t start, remove a spark plug. If the firing tip is gas soaked, it’s likely fouled due to no spark, too much fuel from a stuck carb float, an EFI malfunction, flooding, or the choke being left on. If fouled, heat the tip with a match to burn off deposits.

To check spark, push the removed plug back in its wire connector and lay the plug on the cylinder head so its base contacts the engine. Crank the engine and watch for sparks jumping the plug tip. If there are no sparks or they’re weak, try a new plug.

If the engine cranks but there’s still no spark, you have ignition problems. You might have a faulty ignition module or trigger unit, but first check for loose, corroded, or dirty ignition connections and fuses.

Mechanical Problems
If the engine cranks and there’s both fuel and spark but it won’t start, check compression. A quick test is to hold your thumb over a spark plug hole and crank the engine. If strong pressure blows your finger off the hole, the compression should be sufficient. If not, it’s overhaul time. If the engine was overheated, was run low on oil, and/or spins over unevenly, it may be severely damaged. If you have a damaged engine or clutch, or a transmission or internal parts that don’t operate properly, call a tow truck.

Text and Photography: Ken Freund

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