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YFZ 450 Popping on decel........

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my YFZ 450 quad has the following set up....

Pro-Circuit T-4 slip on, Uni Filter, Ehs Racing lid.

My current jetting is as follows. 168 Main 45 Pilot NCVQ needle on the 4th clip and 2.5 turns out on the screw..

My dilema is this..... during a recent 1.5 hr Hare Scramble I noticed it popping on deceleration..... NOt terrible but It is the first time that I've noticed it... I live in Florida, so I believe my elevation is Sea Level.... and the temp. is normally from 80-90 plus.......

I have noticed at the end of the muffler in the outlet I can run my finger around the inside of the end plate..and it seems just a little smutty.. (black)..... The bike runs good, just curious about the pop......

I've heard people say its from being lean, heard folks say it was rich........ WHats the deal???????

The smut in the end plate seems to say to me that it is probably rich......... WHat to do??????// I do have a 170 and a 165 main in my tool box....

Any help would be appreciated..

Thanks So Much.


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The popping is usually from a lean condition. Your jetting looks rich though and the black soot in the exhaust confirms this. Changing the main jet will not help because the popping is on closed throttle where the main is least effective.

Any exhaust leaks will cause popping on deceleration too. Make sure the pipe is sealed well at the head and any connections.

I would suggest jetting for how the quad runs and ignore the popping initially. See if it runs better in clip position #3 and then evaluate.

The blue marked jetting kit needle is less likely to pop on deceleration due to the needle diameter, which allows a leaner clip position to stay running cleaner. The kit needles also add more top-end without running too rich. The jetting kit is a good option if the Yamaha needle fails to satisfy your needs.


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