And another thread on decel pop


5 replies to this topic
  • Windseeker

Posted May 08, 2008 - 06:09 PM

#1

Got the 08 YZ450F with Yoshi RS pipe.

Pops as hell every time the right hand goes up. No fire though. Turned the fuel screw up to 3 turnes out - helps but only just. Serious gun fire effect is still there. Got the main jet to 170 - no effect whatsoever. Now want to order some needles to try.

Anyone solved it with the needle? The manual is confusing as to the richening\leaning effects of diameter\shape options (clip positions are ok and clear). Which one(s) are the right one(s)? NFLQ NFLP NFPR NFPQ ?

I know the standard is NFLR.

Thanks. :eek:

  • Ga426owner

Posted May 08, 2008 - 06:16 PM

#2

what is the temp and altitude?
I see no need to try different needle yet - NFLR works

  • Windseeker

Posted May 08, 2008 - 06:30 PM

#3

Yes - should have mentioned - alt is sea level to 300 metres. Temp is 10-20 deegresC.

And I read what I could find on "decel pop" and even all pages on Jetting mod on YZ forum :eek:

So I know some popping is racing and ok and theres no air leak on the bike - I had few people check my work :p

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  • grayracer513

Posted May 08, 2008 - 06:56 PM

#4

Decel popping is nearly always either an air leak in the exhaust, which you should always check first, or a lean pilot jet. The needle will have no effect on it.

The leak would more than likely be at the joint of the header and midpipe, although a leak at the head will do it too, as will a leak between the mid pipe and muffler (this is less common even when there is a joint there).

Once you are sure of the pipe. Try this:

http://www.thumperta...ad.php?t=327405

  • Windseeker

Posted May 08, 2008 - 10:40 PM

#5

Thanks - will try a high temp sealant between the header and the mid pipe as there is nothing - just one pipe goes into the other (seems to be "the yoshi way").

And will order richer pilot jets. Will report when done.

  • todds924

Posted May 11, 2008 - 07:54 PM

#6

Got the 08 YZ450F with Yoshi RS pipe.

Pops as hell every time the right hand goes up. No fire though. Turned the fuel screw up to 3 turnes out - helps but only just. Serious gun fire effect is still there. Got the main jet to 170 - no effect whatsoever. Now want to order some needles to try.

Anyone solved it with the needle? The manual is confusing as to the richening\leaning effects of diameter\shape options (clip positions are ok and clear). Which one(s) are the right one(s)? NFLQ NFLP NFPR NFPQ ?

I know the standard is NFLR.

Thanks. :thumbsup:


3 turns out is way to much. You risk the screw falling out if you go past 2 1/2. I am running a pro circuit ti-4 on my 08 and the only thing i changed was the leak jet...from a 55 to a 50. Pro circuit recommends an NFLP needle in the 5th groove and a 42 pilot....I tried it and didn't like it at all. I would also make sure your hot start plunger is closing all the way also. Try keeping the NFLR needle...and use a 48 pilot jet..... about 2 turns on the fuel screw. A 170 main jet will have no effect with your popping and is to big in my opinion for the 08.





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