New needle installed, Popping on decell YFZ450

[svtbolt04]

I have a 170 Main, 45 pilot and NCQV needle on the 3rd clip, air fuel screw is out 2 and a half.

What is making it pop? I run full HMF with pro design box with lid off.

I ran 170 with stock needle, 45 pilot and 3 and a half turns out on air/fuel screw and never popped this much, maybe once in a while, but it had bad problems with the throttle being blipped at low rpms, it would kill the engine.

[Toomey]

How does the new needle compare with the stock one, is it supposed to be leaner or richer or about the same?
Popping on deceleration (high rpms with the throttle closed) is caused by the pilot and fuel screw, and possibly to an extent the needle.  Since you have a fuel screw, with the 3 and a half turns out, you were getting more fuel than at 2 and a half turns.  Try either turning out the screw to get more gas in there with the throttle closed, or go up on the pilot a little bit.  Now, you say that when you nailed it off idle it'd kill the engine, I think that could either be too rich or too lean, depending on how the engine responded.  You might just have to find the right needle that will let you have a leaner pilot and screw setting for jumping on the gas, yet allow enough gas to not pop on decelerating, or just play with the jets.  I'm not an expert or anything, just reading stuff online, so I hope it helps.

[svtbolt04]

That sounds pretty close. But this is the needle they run in the GYTR kit, which is the NCQV needle aka YZF stock needle.

I will probably go back out and mess with the fuel screw, just there is so much to be done to get to it that it makes it a pain.

[Toomey]

I can imagine.  On my RM250, you just loosen the two clamps and pop the carb off, nothing else has to be done.  Jets can be changed in less than 5 minutes, but to me it's still a pain.

[Chillinthemost]

Some people have good luck with a 48 pilot. I run a 45 though.

[Toomey]

A 48 would probably stop the popping, but you might end up with the original problem with the engine bogging when you nail it.

[Chuck_Norris]

if it is any consolation I am running the needle you just installed however I am set up a tad different hope this helps
50. pilot
NVQ on 4th clip
178 main
1.5 turn out on mixxer

I am running the jet for power system and this set up  puts me in the green on all three levels of operation

[shortcut]

Pop on decel. is lean, either go up on the pilot, or try raising the needle a notch and turn the fuel screw in a 1/2 turn.