2005 YZ450f problems Please Help!

Long time lerker first time poster. I have a 2005 450 as stated, and i am having a little bit of a problem. It ran good last year, brought it outta of storage this year and on one of my first rides it started acting up.

My problem is, I can start my bike as usual. I let it warm up a little bit on choke, and the i can ride it around slow jus putting throw the gears. I have a Trail Tech Vector installed to tell rpms and speed and all that good stuff so i can tell my rpms correctly. When I rev the bike the rpms will go up as normal but coming down it will hang around 4,000 rpms for a few seconds then go down to normal idle. Also if I take the bike out and crack it wide open and run it through the gears that way it will run really good then as soon as i let up for a turn or sumthing it will start backfiring horribly and then shut off. i've tried unplugging the TPS without any change.

Any ideas or has anyone had this problem?? I've been trying to figure this out for 2 weeks now. Took it to the shop to have the valves adjusted so I dont think that is my problem and I have tried a smaller pilot jet thinking my low end was rich but it didnt change anything. Tried moving my clip, adjusting the a/f screw. Nothing I have tried has worked.


any help would be much appreciated.

Clean the carb. Make sure the hot start plunger in the carb is seating. Sounds like the pilot is a bit plugged or you have a plugged passage.

I have cleaned every jet in the carburator and i had just replaced the bolt on the hot start cable (plastic bolt into the carb is stupid concept in my book). I have tried a smaller pilot. maybe try a larger one?

Edited by WhyZed450Eff

A "hanging idle" is a symptom of lean idle mixture. You need to verify that the hot start is closing, check for air leaks around the carb mount, and check your valve clearances, since tight intake valves can cause this.

If that passes, go back to your pilot circuit. The discharge port in the carb throat may be blocked with varnish, or there may be varnish in one of the cross holes in the pilot jet. You'll need to go back at least to your stock size, too.

I can check the pilot again but i have soaked all the jets in carb cleaner and blown them all out with compressed air. I have the shop manual on the bike and set all the jets back to what it calls stock. I can go over the carb again but how do I know 100% that my hot start plunger is seated?

The hot start should make a definite, noticeable change in the idle quality as soon as it's opened or closed. If the bike's running lean at an idle, it can be hard to detect, so the best way is often to start it cold, leave the choke on, and work the hot start. It should operate almost like a thumb throttle if you raise the idle a bit.

Alright I'll check that tonight but i had checked before listening for the plunger to slide up and down, which it was.

Deff feeling like an idiot now. Since you had said it was running lean, that got me thinking, I had shortened up my silencer and installed a pro moto end cap on last spring and ran it all year fine no problems. I had taken the spark arrestor out this spring to clean out the pipe and totally forgot about it. Spark Arrestor out = more air flow causing it to lean out. I put it in and adjusted the a/f screw up a little and it runs fine now.:thumbsup:

Spark Arrestor out = more air flow causing it to lean out.
There's something very wrong with a spark arrestor that has any effect on jetting, for one thing, and the idea that a freer flowing exhaust automatically creates a lean condition is one of the most persistent myths in the automotive world.

Well i geuss i was incorrect on what i had thought cuz i jus rode it around the yard a while and its still doin it and it pops pretty bad on decel. :thumbsup: i can't think of anything else it could be... i checked the hot start as stated and its workin fine its not stuck open... idk if it would help but im at around 2300 ft elevation and the carb has a 160 main, 45 pilot, and the clip is one notch down from dead center. air filter is clean and valves have jus been done at the shop.

A leaky exhaust system will cause decel backfire.

any idea if my jetting is correct?

178 main, 48 pilot, 2005 450 starts up easy hot or cold, wont idle once hot, it seems to run good untill warm and then done for the day,,

had hot start issues , i pilled the cable capped the plunger hole with plunger in it. af screw 2 turns out, this bike is new to me, and might be jugged out? how to tell?, 

have a after market slip on exaust, it was acting up on landings bogging wanting to die,.

any help please

Check the o ring for the a/f screw. If its not sealing properly you will have issues. I have had issues with these in the past. Also i usually blow out this passage in the carb with compressed air when cleaning. Just make sure no parts have stuck in the bore that you will lose when you blow it out. Hope this helps. Got to be carb issue if it was running fine when you put it away last year.

Also just to be sure i would dump the tank to eleiminate any possibility of contaminated fuel

Also, im sure you already did this but you should always move the float up and down by hand and make sure the needle doesnt get stuck closed. It should drop easily with the weight of the float. A qtip chucked up in the end of a cordless drill with a dab of polish on the end works great for cleaning up brass fuel inlet seats. Just dont get carried away.

As far as mechanical issues go, a buddy of mines yz450f skipped time which caused really hard starts, but it was not enough to bend valves. So you might look into that as well. I dont think compression is your issue ive seen guys run these bikes with rings so worn they were blowing blue smoke on acceleration.

Edited by NW Briff

would a dimple on the float tab be a problem? or is that suppossed to be there?

bike starts good iddles good for about 1 min then dies.

i was also wondering if i set my float where it shuts off to fast could that create a lean situation like it cant gte gas, and cause it to stall

If the dimple doesn't interfere with the float swinging smoothly in both directions, then it doesn't matter.


If you set the float level too low, it definitely can cause an overall lean condition.  Could also be a clogged fuel filter on the fuel petcock.  Check the flow into a can.

gas flows into can well, she starts and idle good revs up good comes back down, radiator flowing well, and just quit like the kill switch was pushed, , air fuel screw 2 turns out, o ring and washer verified,, is there any part that could when get hot cause this sitiation .,this is frustation,,,, you think you worked it out, runs  fine at home,, load up and pay 25 bucks to ride and well you know the story, not back firing just loses life ,  

175 main 48 pj, ft worth

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