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2011 yz450 backfire/popping

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Please help, I've been trying to figure this one out. 25% of the time my bike will now backfire under engine braking. Valves are in spec. I have replaced exhaust gasket, plug, cleaned entire throttle body and injector, even disassembled the fuel pump and cleaned the filter, and switched gas to different brand. This helped for 1 ride. Now it's starting to do it again. Adding +1 to fuel on map seems to help but doesn't solve. The bike doesn't seem like it's starving for fuel and has no noticeable power loss. Am I looking at getting a new fuel pump? Injector? Any ideas?

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Lean condition when throttle is closed

You have an air leak, or a unpacked muffler, or you are too lean at the idle point

Most likely and air leak, or exahaust and intake valves that are in need of adjustment

You can't remap for idle without using the dealer tool, so you need to make a friend at the dealer.

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Thanks for your response, there is nothing wrong with the valves, I check them religiously, besides the header pipe where else could there be an air leak? If it is too lean at idle could I trick the ecu by adjusting the tps a couple degrees higher?

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I have a 2014 YZ450F that was giving me the same problem. After combing through the bikes valve, muffler packing and EFI mapping, the problem ended up being crappy 91 pump gas I was using from ARCO. Drain you current gas and run a tank of VP U4 through and if you have to use pump gas use Chevron Techroline, problem solved. Good Luck. 

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Did you run straight u4 or mix it down?

I always mix it about half and half with Chevron 91 premium pump gas, however, my head has been modified for more compression. I was just talking to my mechanic about the popping problem and he said to use the unleaded VP race gas which is called T-4 specifically designed for stock 4 strokes engines sometimes the leaded U4 may steal some horsepower from stock engines cuz of the lead, if you did not have the head shaved for more compression, so I would say go with half and half with VP T-4, should fix your popping problem. 

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So the t-4 didn't work. Mixed 50/50 with chevron gas (I always used shell before). Now backfiring is getting worse, I've sprayed contact cleaner all around the intake boots and no change in idle speed(no air leak). It looks like I need to take it to a dealer to remap the idle mixture?

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GYTR makes an awesome power tuner that you may want to check out http://www.motosport.com/dirtbike/2011-yamaha-yz450f--GYTR-POWER-TUNER good luck !!

Already got one. But it does not adjust the map or mixture at idle. It only allows for adjustment for every 3000rpm. 3,6, and 9 where as my problem is when throttle is closed. From all that I have read/done I believe it's the fuel pump, gonna bite the bullet and order one. Let you all know how it goes...

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Ok... So problem got worse until it was stuttering and missing at

0 to 1/4 throttle. It turned out to be the injector

 

Did you replace it  or just service-clean it?

 

Have you been filtering your gas into the tank?

Edited by TheKoolAidMadeMeSick

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Tried to clean it, carb cleaner and air compression. No avail. Replaced it and 2 motos down, calling it fixed

Yes I use a has filter

D@%n phone. Gas filter

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This is the one area I'm really not savvy with, I own a '10 Yz 450 and am dreading any FI problems .... I'm really tempted to get a hold of the dealer mapping tool ( I've found the PN ).

It's good to know that problems are arising and people are finding solutions.

I don't mind replacing a part but I don't want to be replacing parts left right and centre without fixing the problem. I see the fuel line is supposed to be replaced every 4 years.....................

Wonder if it's best to wait til problems arose or bit the bullet and et the injectors serviced etc etc

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Btw what filter are you using ? I'm very careful with only clean fuel going into the tank, I know how sensitive FI is to the slighted bit of debris

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