Backfire from full throttle to fully closed

I think I have my bike jetting dialed in, but am not sure since I am new to the jetting scene. I had the throttle fully opened going down a slight hill, on asphalt, and when I let off (fully closed), it backfired once and then a little popping. Is this normal for a 4 stroke? Does this tell me something about my jetting?

p.s. I also have a PMB insert I just installed

Thanks for any input

use a 160 (60+ degrees) or 165 (cold weather) main and stock needle #5 for the cooler weather in Vail right now. 155 main and stock needle #4 is for the heat of summer. :)

I had a similar problem, but when I started mixing 111 race gas with 92 pump gas the deceleration popping and backfiring went away. I also turned my fuel mixture screw out a 1/2 turn more.

I think I have my bike jetting dialed in, but am not sure since I am new to the jetting scene. I had the throttle fully opened going down a slight hill, on asphalt, and when I let off (fully closed), it backfired once and then a little popping. Is this normal for a 4 stroke? Does this tell me something about my jetting?

p.s. I also have a PMB insert I just installed

Thanks for any input

Backfiring and popping on decel usually indicate a lean condition

on the pilot/slow air circuit.

Lean condition on the Pilot/slow air circut? What does this mean? Do I increase my pilot jet or turn out the fuel screw?

Try increasing the pilot one size...

You really need to rejet you are way to lean everywhere. Your bike sounds like a popcorn hot air popper on decel!

165 main Clip #5 or #6, 48 pilot. Do it all and stop riding lean. :)

I just ordered a JD Jetting Kit. I will be taking the carb off again and when I do I will have a 48 pilot jet to put in with my new jet and needle. Any suggestions on my initial setup with the JD Kit?

At your altitude, I don't think your set up is bad. You could probably get rid of the popping with the fuel screw. A 48pj might give you a a bit more torque off the bottom, but will be a bit rich when you start hitting 10,000'. You will want to use the red JD needle, it is richer than stock, so a 48pj will probably be to rich. Maybe a 158 or 160mj, but I think a 160 will be to big if you stay mostly above 8000', especially as summer arrives.

my wr450 was backfiring on decel. and the only thing wrong was that the idle was set too low.

My bike was idling high and I did play with the fuel screw (+ turns) but that just made the idling higher, I did notice the idle screw when I was playing with the fuel screw, the high idling made me think I might be too lean. I am going to put in the JD Jetting kit and then start on over from there. Thanks for the input and advise. Hopefully I will not have to come back here for more help after this weekend. :)

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