Can't get rid of decel. popping!

[bigshane81]

I have an '04 YZ450F that has popped during deceleration since it was new (but not very bad). I recently installed and FMF powerbomb header and Dr.D exhaust pipe. Before riding it I took it to Capitol Yamaha and had them hook it up to a fuel analyzer to adjust the jetting correctly (I thought). They ended up swapping my needle jet to a WR450F needle for some reason. They explained to me that it ran perfect now. I got home and tested it out in the street at about 50 deg F and it pops now more than ever. Is this normal and will it hurt my enginge? It ran strong and smooth during acceleration.

Thanks, Shane

[Wayward Son]

you need to switch back to the yz needle.the straight diameter if the wr needle is leaner.not what your bike needed.

EGA's do no good unless used in conjunction with a dyno.they only work idle other wise.

[bigshane81]

Ok thanks. I took it back to them this morning and they did have the bike on a dyno. They said it was running a little rich and the excess fuel was burning in the exhaust system, causing the pops. They leaned it out a little and now it pops a lot less. They said it was impossible to eliminate all of the popping without compromising performance. Does this sound right to you? The bike is way faster with the new pipe now and it does run smooth. They also said the popping would not harm the engine. Is that also true?

[Wayward Son]

unless its huge back fires i wouldnt worry.

the answer is yes,any 4 stroke that i have seen that doesnt pop slightly has been to rich at idle.

[bigshane81]

Ok cool. I feel way better about it now. Thank you

[J_Mayday86]

I kinda have the same problem. My 04 wr450f always has popped on decel. This year i let it sit for like four months and when i started it it ran horrible. so i took the carb off and cleaned it thinking that it had gummed up a bit. when i put it back togeather it was popping way worse than it ever has. i took it into a local bike shop and had them look at the carb. they cleaned it and swapped out my main jet saying that it was oversized and that was my problem and put a stock size back in. that didn't fix the problem so they checked the cdi box, tps, valves and timing chain and said that the only thing that they could come up with is that it must be because there is a dent in my header pipe. that doesn't make any sence to me cause that dent has been on there the entire time that i have had the bike and the problem has just started since i took it apart. i checked to make sure that there wasn't a air leak in the boot between the carb and head. there's not. i'm out of idea's. maybe you guys have one. the only thing that i could come up with is that maybe there is a plugged jet that they didn't see?

[jeepn1973]

check your slide plate, it might be upside down. square end goes down...

[dgcars]

I kinda have the same problem. My 04 wr450f always has popped on decel. This year i let it sit for like four months and when i started it it ran horrible......i took it into a local bike shop and had them look at the carb. they cleaned it and swapped out my main jet saying that it was oversized and that was my problem....the only thing that i could come up with is that maybe there is a plugged jet that they didn't see?

Changing the main isn't going to cure decel pop.

If the bike has been sitting for 4 months.....Drain all the fuel from everywhere. Fresh gas needed. Remove the pilot jet & replace it with a new one. That should be it sorted.....?

[J_Mayday86]

i drained all the gas when i first had the problem. but i will check slide and replace piolet jet. i appreciate the ideas and will get back to you guys when i've gave it a shot.

[RichGuy]

Solution: JD jet kit, if it does in fact have jetting opportunities, is the best simple carb update. He recommended running the bike richer than the stock settings. My WR was popping when it was running lean...

[William1]

Letting the bike sit causes a film of varnish to form on the pilot jet. That can be part of your problem. It may be possible a fine tuning of the fuel screw will compensate for it though I doubt it. Usual solution is to simply spend the five bucks and get a new pilot jet.

You also have a device on your carb called the ACV (Automatic Coast Valve) Its' function is to add fuel on decel to reduce/eliminate popping. If yours is not working properly due to a torn diaphragm or weak spring, that can contribute.

Finally, if you run an open pipe, no amount of jetting short of making the bike unrideable will eliminate it all. A muffler, well muffles, and an open pipe does not. Stock muffled bikes pop on decel (the soothing 'burble')you just cannot hear it.

[J_Mayday86]

yeah i was alittle confused about that too. one guy at the bike shop said it was a rich pop and one guy said it was a lean pop. i am going with its a lean pop. not sure the first guy knew much about what he was talking about.

[J_Mayday86]

so william 1, isn't there a good way to bypass or dissable the acv? is it going to help with the problem if i do and is it bad for the bike? i know absolutly nothing about acv.

[highmarker]

I'd leave the ACV intact. If you want to prove to yourself it's working disable it and your pops will become big bangs. You can temporarily block the vacuum port that you see when you take the cover off.

[William1]

so william 1, isn't there a good way to bypass or dissable the acv? is it going to help with the problem if i do and is it bad for the bike? i know absolutly nothing about acv.

You can disable/remove it and it will make the popping worse. Some ACV's are built into the carb, some are mounted externally to it. So that can also vary how you do it.

To disable it, you can remove it and modify the jetting (Removed it acts like it is switched on, so need to lean carb circuits) or you can disable it (the valve is always off or closed or always on/open). This site gives some good info and pictures.

My preference is if you have one, leave it on and make sure it is serviceable. Three parts, a diaphragm, spring and an oring.