2004 Yz450f popping

Hey everybody I'm new here and I need some advise. I have a 2004 yz450f that had a lot of popping on deceleration. I am pretty mechanical inclined I work on bikes all the time but I can't get this one figured out. I first started cleaning carb and checking valves. Everything is good now I have a 150 pilot jet and a 170 main jet. Fuel screw is at 2.5 turns out. I just put a new exhaust gasket in it. I don't know what else it could be I am riding at 0-500 ft elevation, it is about 50 here

Any advise will be greatly appreciated.

Check for crack in exhaust or not sealed good to engine / header?

The header is bent a little bit from a pretty rough crash. Could that effect it any

I went and checked for cracks in the header and there isn't any and far as I can tell there is no leak in the exhaust system anywhere. It does have a slip on exhaust is the the reason for popping should I go higher in pilot jet

45-50 pilot.

... I have a 150 pilot jet ...

No you don't.

When you're looking for air leaks in the exhaust, don't overlook the header/mid pipe joint.

I put a new gasket thing in that to.

My 04 had a dead spot off idle which made low throttle stuff a little jerky. Dissassembled the carb and found one of the crossover feeds(terminology?) plugged. These are 1 small hole in front of the emulsion tube and 3 just in front of that. It was the first small hole that was plugged. Took some time and a couple of copper strands out of a 26 ga speaker wire to clean it out. Reassembled the carb and the off idle response was improved but not fixed and now I had an AWFUL pop on decel problem. Took the carb back apart and recleaned everything all over. The hole wound up being partially plugged but blew out with compressed air this time, reassembled and the bike runs flawlessly. I cant give you a definative reason what my decel pop was caused by but the process above fixed it. It could've been anything from removal and installation or anything in between but I thought I'd share in case it helped. And no I DO NOT advocate cleaning any hole in a carb with copper wire or anything else. If you do the risk is yours.

Yea that's helpful thanks I haven't tried blowing it out with compressed air just use carb cleaner

Be sure to blow from the small side of the hole your blowing through. If it were to have trash it would like need to be "back- flushed". I have a blower that has a pencil thin 5 inch spout on it to get into the carb throat with.

Just wanted to report back I found the problem. It was the vacuum plate seal in the slide was all cracked up. Put a new one in from Motosports.com for $8 and now it's running awsome. Thanks for all the replies.

This is how I made my 2009 yz450f behave itself and stop popping. I set the carb completely stock (my bike had no aftermarket exhaust or engine work done to it and I am below 3000 ft) then I simply adjusted the pilot air screw after buying an easy adjust air screw that you can turn with your fingers. I figured out the perfect amount of turns and now no more popping. It does have a slight bit of hesitation on the bottom end but thats a different story. For that my trouble shooting section in my manual is telling me to set the needle clip position one clip higher and if that makes it worse go a clip position lower. I am going to do that once riding weather comes around. Jetting in the winter is not the best time because its cold. Cold sucks for too many reasons to list.


Thanks for posting follow-up..... happen to see post in daily email yet sadly never replied.

Have (had) same issue riding last winter... yet from other non Yamaha post.... ended up

w/ a fractured sacrum all last year and still an issue..... so still no riding.

Found your reply interesting... since developed about same issue & just chaulked it up

to weather variations w/o any adjustments.... so I'll have to take a look at the vac. plate

seal as well. Or, start making adjustments accordingly....

Tossed a new header pipe this past fall (more for looks) from pitted / rocked, yet + with

grayracer and should replace w/ new at joint.

Good tips from others... and nice to see info relative to an 04.


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