will a header/pipe exhaust leak make an engine run very lean?

ive been having problems with my bike running really lean. theres is a leak where the header connects to the pipe, would that be the the problem. it was running perfect before but since i put as new pipe on its been real lean. i did go up a size with the main, 175-178. im thinkin of usen some kind of shrink wrap or somthin and maybe some gasket maker/sealant. any ideas?

Yes an exhaust leak will cause a lean condition; you can use Chamber Seal or Permatex, Ultra Black. Chamber Seal worked fine on the 2-smoke, but just melted from the exhaust temps from my 4-stroke.

NAPA will have the Ultra Black; you’ll have to let it cure a little prior to sliding on the silencer.

Let us know how it works for, ya!

MXA Mag has a great article about how pipes work on MX bikes and talk about the importance of tight joints and leaks.

does it talk about it on the web site, or which issue is it in?

You say it's lean, but where (at what throttle opening(s)) is it lean? For very small throttle openings (idle to about 1/4) play with the fuel screw and pilot jet. For mid openings (about 1/4-3/4) the needle and clip position will have a significant effect, and for over 3/4 the main jet will have the most effect. I'm not a jetting guru, but this is the basic way it works, hope this helps.

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