jetting is more difficult then I thought!

1 reply to this topic
  • rmx250rider

Posted October 28, 2009 - 04:48 PM


its a 1998 YZ400F ,has the 2005 YZ450F body
out a new exhaust system on it(megabomb and factory 4.1)
Problem is they dont make a megabomb for my bike

and now my jetting is way off( I talked to the same guy I have talked to at FMF with every single FMF pipe i Have had (from 2 stroke to 4 stroke) he isnt the brightest even when the system is made for it

every part of the carb is stock.
I did put in a 178 main when I had the powercore 4
but i now went down to a 175 because the 178 back fired alot and it still back fires a little:foul:
No holes or gaps in the exhaust

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  • grayracer513

Posted October 28, 2009 - 07:36 PM


The exhaust is not likely to make a particularly big difference in the jetting of the bike vs. the stock exhaust, nor is the fact that the MegaBomb was made for a later bike likely to matter much.

Review the user jetting DB, and look at what 400 owners are using for jetting. Also look at any MB equipped later models and compare them to their counterparts with "normal" headers.

Then carefully read this:


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