Ybr engine troubleshooting

[Adampotter]

Hi everyone I have a 2011 ybr 125 that won't start the engine has been rebuilt but won't start in cranks over the timing is correct, it has compression, spark and fuel but it just won't kick over does anyone know what could possibly be wrong any help is appreciated thank you

[Riejufixing]

[Adampotter]

The ignition timing and valve timing are both spot on and the spark plug is in good condition there's no reason it shouldn't run

[spottedtango]

Engine needs 4 things to run fuel/air, spark and compression.

So ones at fault.

Have you tried spraying easystart into the intake? If it starts it’s fuel related

How did you check the spark/compression/fuel?

[Adampotter]

[jeffyjeff]

Your YBR is fuel injected, right? You have fuel in the tank, but since you are sure of spark, ignition timing and valve timing, the next thing to check is fueling. Two thoughts:

1. Make sure you can hear the fuel pump turn on when you switch on your ignition. Maybe you can remove the fuel injector and observe the fuel delivery while cranking.

2. Also, your bike has a tip-over sensor under the seat. It's there to stop the engine and fuel pump when the bike is dropped. Make sure it is not loose or installed improperly. The Haynes manual says voltage between the yellow/green terminal and black/blue terminal (with the sensor connected and ignition ON) should be 0.4-1.4V with the sensor upright, and 3.7-4.4V when the sensor is tilted 65 degrees.

Hope these ideas are useful to you. good luck

[jeffyjeff]

Your post said you can smell fuel, so that rules out the tip over sensor. But you still don't know if you are getting a burnable Air/Fuel mix. Check for an air restriction, and see if you can determine if the injector is delivering an atomized spray. Also, double check that the spark plug is delivering a solid spark. A weak spark cannot withstand the turbulence of compression. just a few ideas that might help.