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comp123

2012 WR450 High RPM Backfire and Stall

23 posts in this topic

Okay, here goes again.  Since my motor rebuild last season, the bike has been running awesome. Now when I accelerate hard the bike backfires and in most cases stalls, in the higher RPMs. The bike starts right back up and will Idle and run fine as long as I don't hit the high RPMs. So, took off the FMF pipe and programmable ECU. Put the stock pipe and ECU back on. Pulled Fuel injector, pressure cleaned with solvent and replaced. Cleaned air filter. Checked AIRBOX and coupler to throttle body. Checked all vacuum lines and electrical. 12volt system, charging and otherwise, good. Changed Spark plug. TPS reads exactly5k. Changed oil.                                                  Went for a ride, got through all 5 gears full throttle several times. Gave it one last wide open throttle and backfire, sputter and stall. Start right back up pulled into the garage and here I am....

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Inspect your stator for metal debris sticking to the pick up

 

Also inspect your plug cap for a cracked solder, and the harness coming off the stator for corrosion.

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The cap is good no cracks.Connections to the stator are good. The stator pickup is also clean of debris.

20160804_172338.jpg

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Did you open up the cap and look inside??

 

It has to be a momentary loss of spark or combustion, not jetting. 

 

I would do a stator test.

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Anyone else? So far I have changed the fuel. Spark plug. Pressure clean the fuel injector with solvent. New coil. New spark plug cap. New air filter. Checked all connections to and from the air box. Put back the stock ECU with the stock exhaust pipe. Checked all wiring and connectors.

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I removed the fuel pump from the gas tank. Everything looks brand-new inside. I have not done a two-minute fuel pressure check yet. I will look into the procedure and get it done.

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Fuel pressure stays at 50psi when running. Is there anything I could look for if I take apart the throttle body? Running out of ideas... :banghead:

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 Where is the pump filter? I saw a screen and it was clean. I did not disassemble the fuel pump, I just removed it from the tank and inspected it.

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Took apart the fuel pump and inspected and cleaned a 1 1/2 by 2 1/2 inch screen attached to the fuel pump. There was zero contaminent.

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Did a compression test came up with 50psi, Seemed low even with the decompression so I did a leakdown. test. Blew 100lbs into the cylinder at TDC. Got 70lbs out, with air escaping from the air filter housing. Going to pull the top end....

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Did a compression test came up with 50psi, Seemed low even with the decompression so I did a leakdown. test. Blew 100lbs into the cylinder at TDC. Got 70lbs out, with air escaping from the air filter housing. Going to pull the top end....

 

Bad intake valve..... :thumbsdn:

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Not sure what's happening yet but this is what the top of the Piston looks like. Going to bring the top half to Yamaha tomorrow to see what they say.

20160817_195027.jpg

20160817_200114.jpg

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