Jetting questions on my 1999 YZ400F

I have a 1999 YZ400F and I want to change the exhaust from the original FMF "Q" muffler to a FMF power core 4 Muffler.

When I last had the carb worked on it was jetted perfectly to the FMF "Q" muffler.

I was wondering if the jetting needs to be changed or will previous jetting work?

I dont know what jetting is in there right now becuase my mechanic did not keep a record of what went in there when they fixed the carb

Do i need to know and how would i find out????

Thanks for all of your help!!!

Patrick M.

I have a 1999 YZ400F and I want to change the exhaust from the original FMF "Q" muffler to a FMF power core 4 Muffler.

When I last had the carb worked on it was jetted perfectly to the FMF "Q" muffler.

I was wondering if the jetting needs to be changed or will previous jetting work?

I dont know what jetting is in there right now becuase my mechanic did not keep a record of what went in there when they fixed the carb

Do i need to know and how would i find out????

Thanks for all of your help!!!

Patrick M.

Jetting is mostly trial and error. Put your pipe on and see how it runs.

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