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Hi guys. So I bought a 2007 CRF450X two days ago, my first ever 450. The bike runs like a beast. The only thing bothering me is the excessive popping on decel, it’s extremely annoying! Though when I pull the clutch in it stops, let it out and it’s back at it again, there a reason for this? At first I thought it was to lean, as that’s normally the cause, but I’m getting mixed search results. Some say it’s to lean, others say it’s to rich - the popping is excess fuel burning of in he exhaust (which is stock btw). I was leaning towards the “to rich” answer as there was a distinct fuel smell when running and black smoke when I revved it high. So I leaned it out (1 1/2 turn out) and the fuel smell is basically gone, and the black smoke is less/barely there, but she’s still popping. What am I to do? I haven’t had a chance to check my jetting yet.

Hello and welcome. You have the dreaded emission model 450X. You need to purchase the block off kit the will eliminate that deceleration pop. The kits are here on the sites parts in the 450X parts section.
That is all you need and will be golden. Enjoy the bike - they are fantastic machines.
Here it is.
https://www.crfsonly.com/catalog/produc ... ts_id/1044

So the popping is nothing damaging or distressing?

So the popping is nothing damaging or distressing?

The popping could also be a few other things , but work on 1 thing at a time so you know what worked and what did not ..... the other items could be valves , easily eliminated by checking the gap **(Do you have a manual ??)** , or the pilot jet may be partially clogged , it is best just to replace the pilot jet with a new #45 and your good ....**stock may be a #42 , but its too lean so go to the #45 as the #42 was used for emission purposes not performance** , also if the bike was ridden at a different elevation than you are (by a few thousand feet) then rejetting may be necessary

Below is a jetting chart to use as a guide to what you should be jetted at , if the smog block off kit does not completely eliminate the popping then follow it and you should be good

Jetting Guide for Main Jet: CRF450R/X

Pilot: 45 (stock #42) all elevations

Main Jet:
Sea level....165
2000 ft.......162
4000 ft.......160
6000 ft.......158
8000 ft.......155


Temperature/Elevation:
One main jet size (up/down) for every 2,000 feet or 25 degrees in temp.

Ok I checked, my bike doesn’t have a smog pump.

I edited my post while you were replying so re-read my last post

So the popping is nothing damaging or distressing?

The popping could also be a few other things , but work on 1 thing at a time so you know what worked and what did not ..... the other items could be valves (easily eliminated by checking the gap) or the pilot jet may be partially clogged (just replace the pilot jet with a new #45 and your good ....**stock may be a #42 , but its too lean so go to the #45 as the #42 was used for emission purposes not performance**) , also if the bike was ridden at a different elevation than you are (by a few thousand feet) then rejetting may be necessary

Below is a jetting chart to use as a guide to what you should be jetted at , if the smog block off kit does not completely eliminate the popping then follow it and you should be good

Jetting Guide for Main Jet: CRF450R/X

Pilot: 45 (stock #42) all elevations

Main Jet:
Sea level....165
2000 ft.......162
4000 ft.......160
6000 ft.......158
8000 ft.......155


Temperature/Elevation:
One main jet size (up/down) for every 2,000 feet or 25 degrees in temp.

Thanks! Could it be the pilot jet cause I started her today and the idle is inconsistent when the choke is on?

I edited my post while you were replying so re-read my last post

I don’t have a manual no. What should the specs be?

It is not a smog pump. If your bike is a 2007 you have the emission crap that needs to be removed. NO the popping is not hurting anything - YES you want to do the block off to get rid of it. Period. NO you do not need to waste time on trying to change jetting or over think this....

It is not a smog pump. If your bike is a 2007 you have the emission crap that needs to be removed. NO the popping is not hurting anything - YES you want to do the block off to get rid of it. Period. NO you do not need to waste time on trying to change jetting or over think this....

Please explain where this is? Cause the hole that plug is meant for is sealed off on my bike. I’m not from the states, we run different configurations.

It is not a smog pump. If your bike is a 2007 you have the emission crap that needs to be removed. NO the popping is not hurting anything - YES you want to do the block off to get rid of it. Period. NO you do not need to waste time on trying to change jetting or over think this....

Please explain where this is? Cause the hole that plug is meant for is sealed off on my bike. I’m not from the states, we run different configurations.

If that is correct and the casting boss on the lower right side of the cylinder is just a casting and no metal tube you have a no emissions model. 2007's and on had the emissions added here in the states. Don't recall all the exacts but some CA models had it and others did not.
But - If that is correct then you need to go one size larger on your pilot jet and the popping will be gone. You are getting a lean condition pop on deceleration. If you go one size larger on the pilot you will probably have to go in on the air fuel screw a turn.
Do you know what pilot jet you presently have installed? I suspect you are 3 or more turns out on the AF screw and still getting the pop? That is also a identifier that you need to step up one on the pilot jet.

It is not a smog pump. If your bike is a 2007 you have the emission crap that needs to be removed. NO the popping is not hurting anything - YES you want to do the block off to get rid of it. Period. NO you do not need to waste time on trying to change jetting or over think this....

Please explain where this is? Cause the hole that plug is meant for is sealed off on my bike. I’m not from the states, we run different configurations.

If that is correct and the casting boss on the lower right side of the cylinder is just a casting and no metal tube you have a no emissions model. 2007's and on had the emissions added here in the states. Don't recall all the exacts but some CA models had it and others did not.
But - If that is correct then you need to go one size larger on your pilot jet and the popping will be gone. You are getting a lean condition pop on deceleration. If you go one size larger on the pilot you will probably have to go in on the air fuel screw a turn.
Do you know what pilot jet you presently have installed? I suspect you are 3 or more turns out on the AF screw and still getting the pop? That is also a identifier that you need to step up one on the pilot jet.

Yes mine is just a casting. Thanks a lot for the info! I think the pilot might just be the solution. As far as I’m aware it’s all still stock jetting. I live right next to the ocean and hardly ever go above 1000ft so I’ll be changing her to 45 pilot and 165 main this weekend.

If you are stock jetting you most certainly want to re-jet. They come from the factory so lean that they barely run. You will find the larger pilot will give the bike a lot smoother acceleration and much less stalling.
You'll like it!