2015 YZ450F 1/2 throttle Back fire on acceleration.1 Ft flames

Brad0199
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Saint Clair, MI US
5/10/2016 7:14am Edited Date/Time 5/13/2016 6:55pm
2015 YZ450F 1/2 throttle Back fire [ LOUD ] on acceleration. 1 Ft flames out exhaust, every once in awhile small/light pop out intake. Engine sounds dull like timing or fuel mixture is off. Has 50 psi fuel pressure, cleaned fuel injector and checked spray pattern. Ohm tested fuel injector, ignition coil, spark plug cap, coolant temp sensor, air temp sensor Installed new spark plug, different coil and boot,new fuel, Tested TPS using 5 volt sweep test. Dielectric grease all electric connections. Checked timing and valves all are right on. I do not have a tuner This bike has 13 hours on it. not hard hours. Any help will be greatly appreciated. Thank you.
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moco
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CA
5/10/2016 8:04am
I would leave it alone. That must look fawkin cool. You should consider wearing a cape to finish the look off.
pete24
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Marlborough, MA US
5/10/2016 8:55am
check the pipe to head gasket , did you put a pipe on it and not replace the gasket?, its sucking air
stevo450
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AU
5/10/2016 9:13am Edited Date/Time 5/10/2016 9:14am
Leaned out because it's getting air in somehow? Just check the exhaust hasn't come loose... Just a bit of a stab in the dark. Any ideas how you know the hours without a tuner? The tuner may offer some insight into the problem.

The Shop

stevo450
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5/10/2016 9:16am
If you removed the injector did you check that the gasket/o-ring was good and sealing? I did read an odd case that had a similar issue and it was leaning out from an air leak with the injector...
Brad0199
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Saint Clair, MI US
5/10/2016 9:39am Edited Date/Time 5/10/2016 9:40am
The exhaust is stock. I will check the exhaust and the injector o ring when I get back home. You can tell it has a problem just by the sound at idle, exhaust is dull just idling. 1 time out of 20 it did start and run fine. Shut it off and restarted it problem returned. It will NOT even lift the front tire off the ground its lacking that much power. Stevo I have a hour meter on it.
Paw Paw 271
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Benton, LA US
5/10/2016 9:48am Edited Date/Time 5/10/2016 9:57am
Sure sounds like a TPS issue. You said you tested it,( I assume at the devise) but have you attempted to trace the wiring and or resetting it?
There is also an outside chance that the starter plunger is leaking air or the TPS o-ring is leaking. Have you attempted to spray carb cleaner around the engine while running to see if the idle speed changes. That may help identify the air leak area.
Have you cleaned the injector?

Paw Paw
Brad0199
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Saint Clair, MI US
5/10/2016 11:28am
Paw Paw I tested the TPS at the devise, the voltage at idle and through the throttle range to WOT. I Cleaned the injector, energized the injector, back flushed it and flushed it, Checked spray pattern. I have not checked the other things you mentioned but I am going to. Thank you for more ideas to try.
CarlinoJoeVideo
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2298th
5/10/2016 4:51pm
I would try a tuner, it sounds like the timing is way off. Did you try and plug in a new ECU?
Brad0199
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Saint Clair, MI US
5/11/2016 5:46am
Last night tried spraying carb cleaner around injector, intake boot etc and no change. Verified 5 volt reference to TPS. Its good. Someone told me a tuner will not give me the info that I will need. I know nothing about a Yamaha tuner. Dose anyone know what info or data a Yamaha tuner gives?
CarlinoJoeVideo
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2298th
5/11/2016 6:44am
The reason I suggested a tuner is because it sounds like as the rpm and throttle position going up the time goes out of whack. Maybe you can reload the maps or just try a different ecu first?
Brad0199
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Saint Clair, MI US
5/13/2016 6:55pm Edited Date/Time 5/13/2016 6:57pm
Well I have done everything that was suggested, Tried a new TPS, That was not it. At this point I'm disgusted with it. I'm really trying not to take it out on the brand of bike but its the first Yamaha FI bike we have owned. Had KTM, Honda FI bikes and never had a problem like this with a bike with such low hours, Not really sure which way to go at this point, guess I can take it to a dealer and pay for them to guess at it or start buying parts until fixed. ECU would be next guess.
mx724
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Cleveland, OH US
6/15/2016 9:11am
Did you have any luck sorting this out? Ive seen these issues discussed enough to follow some of the threads. Please let us know what you may or may not have found.
mario217
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7/27/2016
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PR
7/27/2016 6:31pm
brad0199 did u find what just happened i got the same problem in my yz450f 2014
Brad0199
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Saint Clair, MI US
7/28/2016 7:26am
The problem was the pressure sensor on the throttle body.
mx724
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Cleveland, OH US
7/28/2016 8:47am
You mean throttle positioning sensor?

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