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Popping during deceleration

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I just got a 2005 crf450r. It almost runs perfect, but it pops alot during deceleration (when I let off the throttle). I thought that the pilot screw could solve it since it was between 1/4-0 throttle. when I added more fuel to the mixture it didn't do much at all. what should I try next?

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When's the last time you checked your valve clearances? If your exhaust valves are out of spec, it'll cause gases to escape and pop.

If it's running lean, it'll do the same thing, so you should fiddle around with it a bit more.

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I just did the valves about a month an a half ago. I put in kibble whites. they are just about perfect. they are far within spec

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Yeah, I'd go with lean. Clean the carb and make sure everything is good and clean in in. Then mess with the air screw more, then finally, look for an exhaust leak.

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Popping on decel is almost always a lean condition except as MaybeMe posted  it can also be exhaust valves leaking fresh mixture into the exhaust. 

 

When the throttle is closed with the engine speed above idle there is a lot of vacuum in the intake which can suck in extra air through a leak that might not be noticed at idle speed.  Couple of possibles are the Hot Start  or the manifold. Is the carb clamp tight? 

 

The idle mixture screw delivers fuel during high vacuum so turning it out a 1/2-1 turn or so is an easy way to richen the mixture. If that  has little or no impact then maybe the lean condition causing the popping is from something other than jetting. 

Edited by Chuck.

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Check the pipe.  Might be an air leak.  A little pop is not a bad thing.  I always found if I tried to completely get rid of the pop the ended up being a bit rich and didn't run as well.

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I have the same bike and also just got it, when you have it strung out in fifth gear and then let off and coast us it normal for it to pop? Because in the other gears when I decel and drive it normally it doesn't really do it..

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replace pilot jeticon1.png, with a new one.

or you can do what i do, my jet reamers are not small enough so i separate a strand of copper wire from some 12ga wire i have laying around, stick it through the jet, get some wire cutters and kind of notch the wire 3 or 4 times down the length to make serrations do them 60* or 90* from each other so that it has them on all sides of the wire and drag it back through the jet, spray out with b12 chem tool and compressed air and repeat.

 

also remove the fuel screw, and blow chem tool and compressed air both ways through every circuit in the carburetor

its a good idea to also do the accelerator pump circuit, ensure the nozzle is clear and check the condition of your pump diaphragm

 

you could buyicon1.png a rnd flex screw or merge long fuel screw.

and read about how to get the pilot circuit dialed in this will help you select the correct pilot jet

its been posted you want to use the low slide method

 

and every bike older than 2 years i like to replace the vacuum release plate seal

Yamaha is the only brand that sells it separately

Yamaha part number

4FN-14997-00-00

http://www.kawasakip...64fe/carburetor

its number 11

 

be careful to note the direction of the seal when you remove the old one, its a good idea to lightly coaticon1.png the seal in silicone o-ring grease.

every bike i have replaced the seal in responded by requiring different idle settings and after that had better starting and idle characteristics and off idle response :)

 

a merge accelerator pump spring or ap o-ring mod is a good idea too. but completely unrelated to your problem.

 

also,

id look at the exhaust it only takes a min, fire it up feel around the header flange and the header/muffler connection,

if its stock its probably good,

but my friend put a white bros slip on on his bike, and dude.... there was no clamp period, just a CRAPPY slip fit...

i fixed that put a T bolt clamp on it.

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I just got a 2005 crf450r. It almost runs perfect, but it pops alot during deceleration (when I let off the throttle). I thought that the pilot screw could solve it since it was between 1/4-0 throttle. when I added more fuel to the mixture it didn't do much at all. what should I try next?

 

Here's one that I experienced. ('05 CRF450R)

It was strange because at the start of the moto the motor ran fine, but as the moto progressed, the decel popping got worse and worse and would even stall in the corners if I didn't keep the wick up. I was banging my head because I had gone through pretty much what everyone has suggested and still had the problem. I was sitting in my truck between motos on my Droid googling for answers. Ran across a very short post about the same problem someone else was experiencing that said "check your fuel cap vent hose" - Bingo! I had added an aftermarket vent cap with a one-way check valve. I pulled it off and I couldn't blow or draw through it! I wacked it a few times and the check ball came loose and it then breathed as it was supposed to. No decel popping forever more!

 

May be worth a look at your vent hose, even if it is not a check ball type. I saw a guy blow out a spider web or some insect ball of goo out of a vent hose on a bike that was experiencing idling run-up and lean popping issues.

Edited by tahoemike00
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I have an 06 that was doing that. I put on a crankcase vent kit and it fixed the problem. I know it seems simple, but it worked for me. It re-directs those hot oily gasses that are going back through the carb.

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