Installed the Yoshi slip-on on my Z400. Replaced the jet with a 152.5 (per instructions that come with pipe - up from 130 stock)) Now anything over 3/4 throttle misses and backfires throught the pipe -really bad. Low and mid are fine - starts great, Idles fine - pulls hard untill about 6k rpm (a guess) What's wrong? No mention of doing anything to the airbox (I tried taking the lid off- did not help) No mention of changing the needle clip - is this jet too big? Or does it sound like something else is wrong? Ideas?...thanks...

BTW - I'm at about 1300ft
bummed...

 

Check the plug and see what it looks like. If it looks okay, make sure the float is set properly. Double check everything that you touched and make sure that they are okay. You might wanna take it back apart and check to see if the jet is installed properly. Not to question your ability or anything, but when something like that happens (vehicle runs fine. owner modifies it. runs like cr@p after), it's usually something overlooked. Good luck and let us know.

 

I am not a pro at jetting by any means but from what I know about jetting it sounds like you are way rich. Jetting is really a test of patience. If it stumbles on top it's too rich, if it stumbles on bottom it's too lean, or vice versa, like I said I'm no pro at it. You should get some more info but I would try a smaller jet.

Hope that helps ya.

 

Jetting depends on a few key things. Temp, humidity, elevation, & modification. I would go down on main one size at a time. Make a wide open run & shut engine off before it has time to idle. Check plug to see if it has correct color. White is too lean, black is too rich, gold is just right. Sounds like your needle & pilot(slow) jet are fine.

 

Take Thrshr's advice. Something did not go back together right. Perhaps the brass collar around the mainjet is cocked, or the mainjet came loose...

 

Thanks for all the info. I would have suggested the same stuff if I was asked.

Looks like I may be just hiting the rev limiter...

Changed the plug - no difference
Swapped the Jet back to stock - no difference
Checked carb over - no problems

Note: the Yoshi intsructions call for a small round - turns out I was given a jet with a smaller taper than factory one - I exchanged it for a large taper (Raptor style) - but that made no difference.

Put everthing back to stock and it seemed to go away. (but it turns out, restrictive pipe with big baffle "hides" the rev limiter better).

Called Yoshi tech support - was connected to the R&D team (very nice folks) - told them my story and he asked the usual questions then said he would call me back - called back in about 30min and asked a few more questions but in the end - they believe that I am hitting the rev limiter - bigger jet, free-flow and reduced intake restriction let you get to the limiter pretty quick. Plus the GIANT muffler outet really lets you hear it. New to DOHC, quick-revers -so I guess I need to learn how to shift again [img]i/expressions/face-icon-small-wink.gif[/img]

They have revised their web site jet recomendations to the following (from 152.5 -stock airbox)-

pipe only 125 (odd -mine was 130 stock)
Pipe no snorkle -145
pipe no snorkle no lid 152.5

Tech told me to run 155 though - due to extreme heat here in Phx.

Just FYI - the RS-3 is LOUD! I will be buying the end-cap kit shortly to quiet it down some. On my initial test ride - was tough to keep the front end down - even in 3rd - you don't get to hang out in any gear very long when pinned.

So far my mods are:
PRM skids, bumper (pretty stout - swing arm skid need some hole work to fit though)
Yoshi RS-3 slip-on - looks cool - too loud for me though - paid $399
155 jet
50watt spot mounted on bumper - replaces bottom stock light
removed snorkle
Panoram speedo (bike version)

 

That's what i had wondered. It looks like it doesn't take a whole lot to wake the motor up and start hitting the rev limit. Yoshi is supposed to be coming out with a cdi for this but they will be backordered for awhile.

 

Sure makes sense to me. Just incase, try putting a tach on it.

 

Good to see you have it fixed. You should be hitting like 9000 RPM then, not 6000 right? My HMF sould be here tomorrow and I'll be putting it on once I drill the damn bolts out of my carb bowl and get better once. ^%&^%#^#
Sounds they they all are really loud. About 102-103 db each for the Yosh or HMF. I'm getting the spark assestor so hopefully that quiets it down maybe 5 db.

 

Hope it's OK...Just heard that ALL public lands in AZ will be fully closed as of 8am Friday. This includes all Parks and designated campgrounds. (Except Yuma and Mohave counties)This is due to fire danger.

Just checked and my "testing grounds" has a BLM closure notice on it. Had a trip planned to the Cinders this weekend but that will be closed also.

Right now, there is nowhere to legally ride on public land within 150 miles of Phx.

Will be doing a night run in Glamis I guess. Sux to do mods and not be able to test em....