2009 yz450f backfiring at low rpms...normal??

[rcdude33]

Hey guys!!

Well you know i got a 09 yz450f, well i just put a new twin air filter in it because my stock filter ripped, but i noticed that at lower rpms, my bike was back firing. Not loudd but enough for me to notice while im riding. But my friend said its not too loud like some of them whose backfiring sounds like fire crackers.

But is this normal?? I threw a frsh plug in it, and the bike definately starts up a lot better, and it just runs smoother, but man that backfiring is making me paranoid like crazy. Im thinking its my jetting. BUT please do not tell me its my valves, the bike usually starts 1-6 kicks hot without the hotstart and usually 1-3 with the hot start. I clean my filter every ride and change my oil every 6-8 hours.

Im not used to the backfiring since i came from a smoker. And plus for the last five days it has been super humid and hot out. Here in PA yesterday it was like 90 degrees and humid.

Thanks guys! And sorry for always posting stuff, im just trying learn about this bike and keep her running good as new.

God bless!!!

Alex

[NSF3537]

Should have gotten that FI 09 RMZ. LOL only kidding. Did you take the screen out or just replace the filter. Maybe it's your jetting, or maybe a bad batch of fuel (water). Check your manual for trouble shooting and go through the list.

[rcdude33]

Should have gotten that FI 09 RMZ. LOL only kidding. Did you take the screen out or just replace the filter. Maybe it's your jetting, or maybe a bad batch of fuel (water). Check your manual for trouble shooting and go through the list.

Naaa man im happy with my yamaha hahahaha. But i did not take the screen out. I didnt know you are suppose to.

Also i looked at the plug, its a charcoal color and im thinking its running a little rich. Also i did bend my pipe and i may possible have a leak but im not sure.

Anybody else?

[rcdude33]

Anybody?

[grayracer513]

https://www.thumpertalk.com/forum/showthread.php?p=3710599#post3710599

https://www.thumpertalk.com/forum/showthread.php?p=3350613#post3350613

[rcdude33]

https://www.thumpertalk.com/forum/showthread.php?p=3710599#post3710599

https://www.thumpertalk.com/forum/showthread.php?p=3350613#post3350613

thanks again gray!!!! I really really appreciate it!

[sro2004]

I threw a Yosh full SS/Alum RS2 system on my '09 and had a decel pop from hell. I checked the install to verify no leaks, then ended up going with a 48 pilot.

Love my '09...

[NSF3537]

Naaa man im happy with my yamaha hahahaha. But i did not take the screen out. I didnt know you are suppose to.

Also i looked at the plug, its a charcoal color and im thinking its running a little rich. Also i did bend my pipe and i may possible have a leak but im not sure.

Anybody else?

I'm not saying you have to take off the screen. It sounds like you are rich. The plug should be more of a consistent brown color. Good luck with your new bike. I still think you should have gotten the new 09 suzuki (FI). Thats just me being biased. I actually like the 2011 Yamaha's but that will never happen. The bike I have is the one that has to last. Now that I messed up my leg real bad my wife does not want me to ride anymore. We will see.

[grayracer513]

But i did not take the screen out. I didnt know you are suppose to

You're not supposed to. It's there for a reason, and dyno tests have shown no measurable gain from getting rid of it.

[NSF3537]

You're not supposed to. It's there for a reason, and dyno tests have shown no measurable gain from getting rid of it.

Maybe not by itself, but it makes a difference combined with other mods. On my RMZ 450 I have the screenless No-Toil, FMF Powerbomb wth 4.1, and Dyno Jet PC 5 mapped for what I just mentioned. Made a difference. I don't kow if it is worth the money, but definate difference mid to top end.

[rcdude33]

I actually got a better deal on the yamaha but I like my yami better. Im Gina get a new exhaust for it and I'm probaly going with a drd. I just want some more bottom and mid. I heard from the drd you can get pretty good gains. I'm just hoping I willnotice the difference in power.

But I think I'm running a tad rich, but should I adjust the fuel Screw or pilot?

[grayracer513]

Maybe not by itself, but it makes a difference combined with other mods. On my RMZ 450 I have the screenless No-Toil, FMF Powerbomb wth 4.1, and Dyno Jet PC 5 mapped for what I just mentioned. Made a difference. I don't kow if it is worth the money, but definate difference mid to top end.

You did three things concurrently, then arbitrarily assigned them all the same value, then? Hardly scientific, in the first place, and the RMZ has a reputation for badly needing a better exhaust system.

Besides, the air box and flash screen on a '98-'09 YZF is what I'm talking about. Doug Henry's Supermoto team did some extensive dyno testing of a number of alternative configurations of the intake that included swapping and modifying air boots, holes in various locations in the air box, and removing or leaving the screen in place. One of the results of the test was that the screen had no effect on horsepower one way of other, so they left it in place. This is true simply because the air filter itself is considerably more restrictive than the screen is.