06 yz450f backfiring when reving engine

friend got 06 yz450f today and it backfires bad when reving engine up, air cleaner was real dirty, cleaned, changed plug checked timing marks on cams, ok, unpluged tps no change, cleaned out carb. nothing real bad inside and set air screw to 1 3/4 out, don't know about stator or cdi box any info would help, thanks.

Clean your carb, especially the pilot jet/circuit.

Check exhaust junctions for leaks,also check the hot start,make sure it is closed .

took all jets out and cleaned, even undid cable from hot-start to make sure no tension on cable. exhaust is tight. has aftermarket headpipe and power now in carb., but has been removed at this time.

took all jets out and cleaned, even undid cable from hot-start to make sure no tension on cable. exhaust is tight. has aftermarket headpipe and power now in carb., but has been removed at this time.

What is the condition of the head pipe gasket?,the one that sits inside of the exhaust port.It is back firing when on the throttle?

did not pull off headpipe to check, when you crack the thottle at about 1/3 opening it cracks and backfires pretty bad.

How old is the gas? The float level was not disturbed correct?I know it is very simple,but try a new plug same heat range of course.

Gas was replaced, same plug cr8e, float level was unchanged and looked to be within spec.

Check the pilot jet. '06's were built with 42's, but at your altitude, they should have a 45. That, and a correctly adjusted idle mixture screw will take care of most of it. Some crackling on decel should be considered normal.

Being how warm out it is and being on the gas at 3rd throttle the 42 pilot has no bearing. It is backfiring when on the gas.

Check the things I mentioned,it sounds like it is a used bike from someone else.This is the first day he rode it,correct? I would go over the carb to make sure it has the stock needle,needle pos,main,make sure the needle isn't damaged or worn. Who knows what the previous owner has done. Just make sure everything is stock with the carb.

when you cleaned out carby did you take note which way the plate on the front side of the slide was fitted! it can be put in upside down. the flat side has to be down

did not pull off headpipe to check, when you crack the thottle at about 1/3 opening it cracks and backfires pretty bad.

I am here in Ga (900-1200Ft)and my 06 can not use a 42pj, w/o tons of popping. 1/3 throttle is PJ related. Try a 45pj and a 168mj, needle at 3rd clip. (I prefer a NFLR or 07 needle). Play with Fuel screw - 1.5-2 turns out - make sure you have oring on the fuel screw. Also you mentioned the Hot start - if the plastic nut is semi worn out - air will leak into this/water does anyway - replace with Alum nut. I assume the hotstart is sliding up and down in carb correct?

Do not test on a stand - the bike has to be ridden.

Ditch the Power is not now.....it will only complicate matters.

Sounds lean to me, and that GA450 might have ya taken care of.

One other thing to consider (not sure how succeptable this bike is to it YET) but if you get a tank of fuel that is particularly heavy on the Ethanol, it can cause the bike to run lean. Go to a station out in the boonies that gets regular gas still (alot do, just not in the bigger cities) and try it out if all else fails.

My dads DRZ650 with its stock jetting would run lean as piss with ethanol blended fuel, but ran fine on regualr gas. It was just borderline lean with regular gas. So some jetting had to be done to make it compromise for both fuels.

3rd throttle is the needle it has nothing to at all with the pilot,come on.

thanks alot for quick responces ordered new jets and will move needle to #3 location, even ordered 2 sets to see if I can clean mine up also. ga450 do ya ever get to durhamtown if so let me know, we got a good little group of guys 35+ year old riders.

I plan on going there soon. Just getting back into dirt after about a 7 year hiatus....... im only 28 though.... hope im allowed :thumbsup:

I go there every once in a while - nice place and Mike is great. I prefer mx but I may get me a KTM and become more of a woods rider

3rd throttle is the needle it has nothing to at all with the pilot,come on.

ok IYSS....but his needle is stock and clip needs to be on 3rd position.

I have an '06 and experienced the same backfiring. I tried some different combinations and settled with 45/168 combination and left the needle stock suggested by grayracer. The bike is a whole new bike, very little backfire and pulls strong (especially mid band) all the way thru.:thumbsup:

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Similar Content

    • By Samx22x
      Alright so I’m new to the site so maybe this question has already been asked. I have a 2002 Yz426f and I want a new exhaust, it has the stock header and silencer and sounds amazing but I’d like a little more from it, I know I want the fmf power bomb header and am kind of undecided on the silencer, I see on fmf’s website that their silencer will add low end and slightly take from top end and the other way around but I’m looking for increases throughout rpm range. I do a lot of trail, hill climbs, jumps, and wheelies so kind of need good performance everywhere in the rpms. My question is what silencer I should get and the jetting I should get for the carb. Thanks
    • By Zack Ailing
      hey guys just picked up a new project bike. Its a 2008 Yz450f with a big bore kit and a stroker crank. The total cc of the engine is now 499. It runs on race gas and will be an absolute monster when shes ready to rip. I will continue to make more videos on the bike so stay tuned Link to the video: 
    • By High On Octane
      2005 YZ450F, Athena Big Bore, Power Bomb, Q4.
      Ok.  Last fall after a decently hot day at the track, I noticed coolant leaking from the weep hole on my water pump after pulling into the pits.  Ordered an Athena re-seal kit, put it all back together and didn't really get a chance to ride it.  3 weeks ago, went out to the track, and after about 20 laps, it started leaking again.  Kept filling it with water to get thru the day, never ran anywhere close to dry or empty, jut a cup or 2 low.  Ordered a Hot Rods re-seal kit with bearing and also ordered a new w/p shaft.  Did it all again and got it back together, ran it, and as soon as it got to temp, it was leaking out of the weep hole again.
      So, what the heck am I missing?  I'm totally stumped on this one.  Is something wrong with my case cover?  Do I need to replace the w/p itself?  I'm feeling like I should've just ponied up for the Boysen in the first place, and now it's biting me in the butt.  Any help or suggestions is greatly appreciated.  Thanks!
    • By Awheeler25u
      Alright guys, my 04 YZ450f runs fine minus some slight backfires when decelerating (need to adjust fuel screw). The other day when I was done checking my valve clearances I changed the oil and filter and put the bike back on the stand, kicked it a few times without the ignition coil in to get some oil flowing got off and noticed a little drip spot on the ground, it was no bigger than a dime so I thought nothing of it. Started the bike with no issues took it for a quick 10-15 min ride, came back to the garage to find out my whole case was soaked with oil and it started pooling in the low spots on the clutch basket side. I cleaned all the oil off and took it out again for 5 mins to try and see where it was coming from, here are my three possible places but nothing directly leads me to believe it’s any of the three either.
      1. Decompression plug area
      2.  Valve cover gasket leak (not really sure because the amount of oil leaking Looks to be a large amount
      3. Oil tank (bad weld or cracked weld somewhere
      what are you guys thinking?
    • By bofar
      Hey guys. I could really use your help diagnosing an issue that came up riding today. Bike is a 2013 YZ450F. Well maintained and haven't had any issues until now. Both the oil and coolant are new and levels are to spec. 
      After riding for about an hour in the sand dunes, I noticed a grinding going on on the right side of the bottom end (from what I could tell). When I looked to see what was going on my kickstarter was vibrating and grinding really loud. This was a different sound than if you engaged the kickstarter while running. It sounded less "clanky" and more "vibrating/grinding" if that makes sense. Grabbing the kickstarter and moving it didn't help the issue.
      When I noticed it, I shut the bike off and gave it a second. Being a few miles deep into the dunes, I had to get it out of there so I started it back up and it seemed fine- no grinding. I headed back to the car and after a few minutes, it came back so I shut it off again, started it back up and nothing. That process happened one or two more times before I made it back to the truck. Seemed to run fine otherwise. 
      Once I got it back to the truck I started it up and tried to pay more attention to what was going on but it wasn't doing it. I did seem to have more of a metal on metal noise coming from the motor. I started and stopped the bike a few times and after the motor stopped there was a distinct metal clank/grinding noise that happened right after the motor shut of for maybe half a second. This doesn't happen every time. 
      I tried doing some research and have seen things that make me think it could be the spring that connects to the kickstarter, or the kickstarter stopper plate- but really I have no idea.
      Seems strange that the issue is off and on.
      Thanks for the help!