2016 Yamaha YZ450FX Bogging

[ToyHauler]

2016 YZ450FX
Did the top end, replacing the piston, wrist pin, and rings. Cylinder looked very good. Cleaned up the valves, replaced valve oil seals, and put it back together. Got the cams lined up, rotated the motor by hand a couple times, back to TDC and checked valves. Valves are in spec, at the looser end, but within spec. Starts right up and revs nicely. But, anything past quarter throttle it bogs and pops. Checked valves again, same and still in spec. Did a leak down test and it’s at 4.4%. Pulled the fuel pump out and put in an All Balls rebuild kit, no change. Fuel is new, clean ethanol free. Spark plug is clean.

Recommendations on what to look for?

 

[dooman92]

Sounds like a fuel issue. I assume it was fine prior to rebuild. Could the fuel injector have picked up some debris. Needs more fuel with more throttle. Stock ecu? My fx didn't like a pr2 vortex. Vacuum leaks in intake track? throttle position sensor get knocked out?

 

[mxpetersons]

Well, as so often is the case, the problem was found between the handlebars and the seat. Took the tank, and intake out and identified I had not connected the Intake Air Pressure Sensor at the throttle body. Amazing how much better it runs!

 

[jarred kale]

2016 YZ450FX
Did the top end, replacing the piston, wrist pin, and rings. Cylinder looked very good. Cleaned up the valves, replaced valve snaptube vidmateoil seals, and put it back together. Got the cams lined up, rotated the motor by hand a couple times, back to TDC and checked valves. Valves are in spec, at the looser end, but within spec. Starts right up and revs nicely. But, anything past quarter throttle it bogs and pops. Checked valves again, same and still in spec. Did a leak down test and it’s at 4.4%. Pulled the fuel pump out and put in an All Balls rebuild kit, no change. Fuel is new, clean ethanol free. Spark plug is clean.

Recommendations on what to look for?

Did you check the injectors ?