What the heck happened?
Gas, air and spark. Must have all three to ride and if your dirt bike suddenly died you're missing one of them.
The dead engine ruins Motos or a good day of trail riding and always brings a bit of choler. It often happens with little warning and the reason runs the gamut. But when decoding this frustrating malfunction just remember - gas, air and spark.
Before you look a bit silly, check the fuel tank. It's happened before. Did you run out of gas? If not, move your way down the fuel line for obstructions or kinks. Check for a clogged jet or a broken fuel pump. Remember back - did the engine shut off during an extremely rough patch? Fuel splashing around inside the tank might cause a brief interruption in gas siphoning through the fuel line which is enough to cut the engine. Try starting the engine again, see what happens.
OK, now move on to the air. A dirty air filter or any blockage in the intake prevents the correct fuel to air ratio. A rich running engine tends to bog when opening the throttle or backfire so you can often address the lack of air issue before facing a dead engine because you'll already experience performance problems.
Weak compression occurs when air bypasses the rings, valves or gaskets. The bike might run well for a few minutes but after heating up shuts down and won't restart until the engine cools. The usually means the valves passed the wear limits and need replacing. Worn out pistons, piston rings, cylinder and other head problems also cause low compression.
Finally, the spark. Now you're dealing with electrical issues and sometimes a bit more complicated fixes. Check the spark plug, this is your best bet for getting back to riding right away. Otherwise check the stator (look for bad winding) and the coil pack (look for poor grounding) as both cause a weak spark when malfunctioning. You'll need an OHM meter for this (sorry! we don't sell them) to check against factory spec - but for spark related issues you might find this BikeMaster spark tester comes in handy or this Motion Pro.
On 2-strokes, a rich premix ratio might prove too much for the jetting system which decimates the spark plug rather quickly. On 4-strokes an over feed of fuel especially on carbureted bikes also results in a foul spark plug.
Combo of the Three
Today's technological advances also come with downsides because the more bells and whistles you have the potential for problems later. Dirt bikes no exception. A defective ignition system, electronic fuel system issues and fuel delivery problems, just to name a few, stem from electronic (the spark) which affects gas delivery.
Unfortunately it only gets worse from here and if you haven't contacted a trusted mechanic by now it's probably a wise choice. A faulty ECM, poor wiring and other shorts prove hard to find without specific tools generally reserved for professionals. It's also easy to overlook bad bearings which can affect engine RPMs or the rod and piston. Or how about the gap between the flywheel and the pickup set? Engine vibrations and even contaminated oil can affect the gap's spec.
The dead engine is like a flat tire - ride long enough and you'll eventually experience it. Usually, it ranges from the easy quick fix to an afternoon project at home. But once you get into the more technical electrical aspects or you just can't find the problem take it to a mechanic with the right tools and know-how to get you back riding.
For additional engine related issues on your dirt bike, check out:
Written By: AndrewT