Still popping on decel. (gray!)


12 replies to this topic
  • Jake92

Posted May 15, 2009 - 05:31 AM

#1

Changed my crush washer, sealed head/slipon connection, cleaned carb. My question is can you describe the slide plate installed correctly? How do I know if it is upside down? Thanks
2006 yz 450

  • grayracer513

Posted May 15, 2009 - 05:57 AM

#2

#10 in the picture. If you haven't had it out, there's no reason to think it's upside down for one thing, and for another, the slide plate being inverted won't cause decel backfire. If the plate is upside down, it will idle fairly normally, and run OK at full throttle, but run extremely rich and miss badly at everything from off-idle to about 3/4.

To repeat something, your bike should backfire on decel. It means it's jetted right. The real question is how much. 2~3 pops or so 2 or 3 out of 4 times decelerating is normal, with it being more prone to it at lower altitudes and cooler temps. Worse than that, your pilot may be lean. If you try to chase it all away, you'll end up with a too-rich idle and starting problems.

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  • Jake92

Posted May 15, 2009 - 07:18 AM

#3

I have had the slide out. THis is something that has came about when I attemped a JD jet kit. I am now back to stock stuff due to other problems but my setup is a 170 main, 48 pilot. Fuel Screw whereever. My popping gets better at 4 turns out. But I cant ride it like that of course. I just dont get it as I never had this before. If the seal on the top of the carb above the needle is leaking could this do it?

  • grayracer513

Posted May 15, 2009 - 07:47 AM

#4

An upper chamber air leak should not cause it run lean, no. Are you quite certain that your hot start is seating/closing?

  • Jake92

Posted May 15, 2009 - 08:52 AM

#5

I will check tonight. Thanks for your help. Ever seen a carb boot leak?

  • grayracer513

Posted May 15, 2009 - 09:06 AM

#6

Yes, but it's a little unusual. If you suspect an external air leak, one way to check for it is to use a combustible carb spray like Berryman's B12. When this spray gets drawn into an air leak it raises the idle noticeably. Not all of them will do this, and obviously, caution should be used when spraying flammables around a running engine.

The carb boot can shrink, and as the clamp is limited insofar as how tight it can clamp down in order to both avoid cutting the rubber and help it stay tight, it can get to the point where it doesn't cinch up on the sleeve enough. If the inside of the sleeve seems wet, or the carb seems able to move around in the sleeve, try replacing it.

Also check to see if the O-ring on the pilot screw is cut or missing.

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  • jjsmx

Posted May 15, 2009 - 11:02 AM

#7

These bikes run lean on the bottom. I put a 48 pilot jet on my bike. The popping stopped after opening the thing up.

  • Jake92

Posted May 15, 2009 - 11:05 AM

#8

Will check. Thank You. JJ--I have a 48 in there now. I am at 700ft elevation

  • jjsmx

Posted May 15, 2009 - 11:32 AM

#9

Will check. Thank You. JJ--I have a 48 in there now. I am at 700ft elevation


hmmm, if you haven't already, try letting it out some more. I actually had to let mine out again after I had my local yamaha shop work on the carb. I was popping like mad even with the 48 in there. My buddy runs a 50! I would say really open it up then go to plan B.

  • grayracer513

Posted May 15, 2009 - 11:51 AM

#10

Will check. Thank You. JJ--I have a 48 in there now. I am at 700ft elevation

My '06 is setup at 45/165/NFPR(stock)-4 and I run it from -80 ~ 3500 feet.

  • Jake92

Posted May 15, 2009 - 06:32 PM

#11

Uggggg. I put the slide plate on upside down. I know you dont think it would cause my problem but It must have an effect. I will try it out in the morning down the road as it is raining cats and dogs.

  • grayracer513

Posted May 15, 2009 - 08:22 PM

#12

Well, if it makes you feel better, you aren't even close to the only person to have ever done that. If you don't think about it too much, it actually looks like it should go in upside-down.

Decel backfire can be caused by being really excessively rich, too. The thing that made me write it off was that you didn't complain about it running badly, just backfiring.

  • Jake92

Posted May 18, 2009 - 05:23 AM

#13

Just to put in some info for the next pour sap that has this. The bike ran great as long as it was not idling or decelerating. Rough Idle and also I had to have the idle screw like a half turn from bottoming out. These were my symptoms, for my slide plate being upside down. Remember, Square hole down!! Thanks gray for your help. Your wisdom on here is priceless.





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