help with poping

[justin j]

k now that i have it idling good now it keeps popping on deceleration it has a 168 main jet and 45 pilot we tryed putting a 165 main but i think it mad it worse the only think the bike hason it is a pro circuit pipe can any one help ?

[Lankyrider]

Have you adjusted the fuel screw? Also try to change the needle's clip position and see what happens.

[dirtytrixx400]

keep going richer on the pilot jet.

my 01 yz426 with fmf powerbomb header and powercore4 required a big step up on the pilot circuit. i'm running a #55 pilot and a #165 main....no popping ever and i don't think you could ask for a better running bike.i'm only posting my jet sizes that i'm using to give you an idea of what it took to get mine right.you will need to do some testing to find what works best for your bike...

[grayracer513]

Also try to change the needle's clip position and see what happens.

keep going richer on the pilot jet.

Bad advice.

The needle and main jet have nothing to do with popping in the exhaust during deceleration, for one thing. As for richening the pilot endlessly until the pop goes away, you'll end up with the bike so fat on the bottom that it will stall frequently, and hot starts will become next to impossible.

You failed to state the model and year of your bike, but judging by the jet range in it, I'll guess it's a YZ450, and those jets are close enough to work.

One of the overlooked and common causes of decel backfire is an air leak at the exhaust, either at the head, or the mid pipe joint. If that doesn't fix it, look at the carb mount to be certain it isn't leaking air, and check the hot start to be sure it closes. When your engine is cold, running with the choke on, the hot start should act a bit like a thumb throttle. If it won't, check the cable, etc.

After that, you can dial in your pilot until the idle is right. Read this thread:

https://www.thumpertalk.com/forum/showthread.php?t=327405

If you can't get the pilot to set up correctly at all with a #45, it's possible that there is a layer of varnish in the jet. Be sure it's clean.

SOME POPPING is normal, and is an indication that the bike is jetted correctly. Assuming everything else is right, if the bike pops a lot all the time, it's lean; if it never pops, it's rich. A pop or two on every second or third decel is about right.

[Gunner354]

k now that i have it idling good now it keeps popping on deceleration it has a 168 main jet and 45 pilot we tryed putting a 165 main but i think it mad it worse the only think the bike hason it is a pro circuit pipe can any one help ?

Here we go!

What part of Cali are you riding? I know Gray will disagree but he rides in a very dry warm climate. Everyone I know with a 450 in Northern Cali runs a 48 pilot. Don't be afraid to bump the pilot to a 48.

[grayracer513]

Here we go!

What part of Cali are you riding? I know Gray will disagree but he rides in a very dry warm climate. Everyone I know with a 450 in Northern Cali runs a 48 pilot. Don't be afraid to bump the pilot to a 48.

If you follow the outlined procedure, and the engine actually needs a 48, you'll find that out.

And there's no indication from his post that he rides in NorCal as opposed to southern or central, or even that he rides a 450, so any such arbitrary recommendations are poorly founded.

[justin j]

srry about that ya it is a 05 yz450 and we live in san diego but thanks for all the advice going to try everything and get back to u guys thanks again

[dirtytrixx400]

you can't state a particular jet size that will work for all bikes or conditions...that's bad advice.

a lean pop on decel is just that....lean.

like i stated he needs to test for what works best for his bike.

you CAN have a bike that cranks first or second kick....everytime(hot or cold).....idles perfectly(no hang idle)....runs cool/normal engine temps(no coolant puking)....and NO lean popping on decel.

you just have to make the effort to do the testing and keep your thoughts on what your trying to get accomplished.

just for the record my bike would only run with the choke on with a #48 pilot with my aftermarket exhaust....way too lean.

[grayracer513]

a lean pop on decel is just that....lean.

And a rich bike with an exhaust leak will pop off like a Gatling gun. Jetting to cure a non-jetting issue will get you nowhere, so first things first.