Backfire from full throttle to fully closed


10 replies to this topic
  • Redwoods

Posted April 12, 2004 - 05:31 AM

#1

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

  • Indy_WR450

Posted April 12, 2004 - 07:41 AM

#2

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. :)

  • JVP

Posted April 12, 2004 - 09:28 AM

#3

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.

  • N7SLC

Posted April 13, 2004 - 02:53 AM

#4

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.

  • Redwoods

Posted April 13, 2004 - 04:25 AM

#5

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

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  • N7SLC

Posted April 13, 2004 - 03:50 PM

#6

Try increasing the pilot one size...

  • Indy_WR450

Posted April 13, 2004 - 04:35 PM

#7

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. :)

  • Redwoods

Posted April 14, 2004 - 10:42 AM

#8

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?

  • lipskid

Posted April 14, 2004 - 05:28 PM

#9

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.

  • Malve

Posted April 14, 2004 - 06:26 PM

#10

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

  • Redwoods

Posted April 15, 2004 - 04:20 AM

#11

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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