market dynamics
The motorcycle cannot be started after backfiring. It is rare to find the fault cause after inspection
Release date:2020.09.15

Recently, maintenance of a straddle motorcycle encountered a problem, was due to the failure of the car's connecting rod, start test, carburetor appeared a strong backfire, the engine shut down, from now on, no matter how to start, the engine can no longer start.

I was puzzled by this fault. The engine could not start, but it was caused by a fault in the electrical circuit, oil circuit or mechanical compression system.

Unplug the high voltage cable and check the spark plug jumping situation. The spark is strong. It should not be a problem with the ignition system.

Readjust the carburetor to make sure the mixture enters the cylinder, but the fault still exists.


Use your finger to plug the spark plug hole and step the starting rod to check the compression pressure in the cylinder. At this time, you feel the pressure is too small. Did you pull the cylinder? Or is the ring worn out? Solve this kind of problem temporarily old master knows, solve sealing problem to be able to affirm first.

Then from the spark plug hole into the cylinder block to add a small spoon of oil, the oil added after the cylinder wall, can temporarily solve the cylinder sealing problem, but the engine still can not start. This is really strange strange!

There is oil and electricity, and there is no air leakage in the cylinder. Is there a problem with the ignition time?

But, open the magneto side cover, remove the rotor magneto, check the ignition time. At this point, a dramatic scene appeared, unexpectedly found the left crankshaft oil seal off.

How did the oil seal come off in this place?

Later, I analyzed that it may be due to accidental reasons, such as improper ignition or improper mixture ratio, so that the burning combustible mixture temper into the crankcase, resulting in a sharp rise in the pressure inside the crankcase, the left crankshaft oil seal was squeezed out under the action of high pressure gas.

A leak here, when restarted, will cause the mixture to be too thin, the compression pressure in the cylinder is too small, so the engine cannot start.

Found the reason, the solution is very simple, in the inner ring of the oil seal coated with a layer of grease, found a self-made weighing hand tubular tool, carefully knock the oil seal into the crankcase. Start test run, troubleshoot.