Help With Revving High

[blueoval]

Could use some help with a 2000 k5 that is stock except for Procircuit pipe and FMF silencer.  After high speed and some WOT it will rev a little high like it is lean.  Not crazy high, but just high.  It will do this for about 15 seconds and then come down.  If I lug it it will come down to an idle.  It doesn't do this at low speeds.  It starts in 2-3 kicks when cold, 1 kick when warm, idles good, runs strong.  I ride at 1000 - 2000 ft above sea level and the temperature has been 45-55 degrees farenheit.  I performed leak test as suggested and it held 7 inHg of vacuum for 15 min.  I pressurized the engine to 6 psi and it held for 6 min. 

Compression is 150 psi
Carburator Jetting:  Main           168
                           Pilot            58
                           Clip (stock)   3rd position
                           Air Screw      1 3/4
                           Float            15 mm (by Clymer Manual)

Fuel is 91 octane pump gas and Golden Spectro at 32:1
This is what the plug looks like after stretch of WOT and immediately shutting down the engine.

Any help would be much appreciated!   B.O.

[DoldGuy]

B.O.,
Sounds like your bottomend is tight by your tests. This might be redundant info, but it sounds like you are running a little lean on the pilot circuit. Based on your settings (& that plug looks good) I would try the same riding condition & when you chop the throttle & it still is hanging on to some revs pull the choke lever on & if the revs immediatley drop, then you know it is a little lean. From there, try the air screw at 1/2-5/8 out and re test, if it is better at those settings, then go to a 60 pilot and re test again. Out of curiosity what Slide # is in there? Also keep in mind that a 32:1 mixture is a Heavier Specific Gravity then a 50:1 ratio & may need a tad richer setting.

[Larry Wiechman]

 Could this be as simple as a sticky slide?
 
Larry

[Hillclimb#42]

Mine seemed to do this a little when i had the idle set too tight. Maybe temp drop has leaned you out a little. You are lucky to be out riding it. Freezin' Balls here. Almost too cold to work on them.

[Friar-Tuck]

 B.O.,
  The pressure testing checks out the bottom end.   That surely reasons out the seals and or case leak.

 The other post in reference to the slide, there is a number stamped on it,  lower number = less taper   What the cut-away does is change the air velocity over the main needle jet.

The electrode and the groundstrap look good, get a light down where the ceramic meets the metal in the plug. That small ring is what you'll want to look at for burn color or "Mixture Ring".
        http://www.strappe.com/plugs.html   (I can find color photo's if you like )

   The "choke test"  is a great idea to quickly check need for more fuel.  The 32:1 I think is what might be a little different as the majority of guys run a little less oil/fuel.
  Not that it's bad mind you.  Especially if you have alot of space to run WOT.  Our jetting will seem alot leaner as we are putting more fuel thru the bike at 40 or 50:1 , hence a 52,55 pilot where as you might need a larger pilot to get the same amount of fuel through the engine.
   
"By the Book"  @ 50deg  with the correction factor of about 1.03 x 58 that would be 59.74 on the pilot (or a #60)
   and with the same correction factor of 1.03 x 168  that would be 173.04    on the main  (or a #173 main)   
    with no change on the clip position and the #7 slide (or all the stock stuff)
  Now this is estimating around 50 deg F and 1500'     
  It looks like you would be right on at 70 deg or so with the pro circuit jetting specs.  (KX500     168     58     N82M  3RD  7)
This is with the owners manual pgs. 86 & 87.
   Just something to consider..

I'm not sure this is lean enough to cause that high idle hang or not..
   Hopefully some more guys will have more Ideas...
     Tuck\o/

Apologies for the large photo below, I don't know how to resize it!

[blueoval]

Thanks everbody for the input.  #7 slide.  The throttle slams shut when the bike is off.  It has a new throttle cable and the throttle tube and mechanism work perfectly (first thing I change when I bought the bike because it had a sticking throttle and it caused the PO to wreck and break his arm). 

[KXcam22]

Blue oval,
  I think from your description that you might be confusing surging with a high idle.  Surging happens to all K5s when they are jetted spot on.  Your jetting and plug look good.  Do a search for "surging" and see it the descriptions match what you are feeling in the bike.  In cold weather with a lean pilot you can also get some lean idle runaway that goes away as soon as the outside temp warms up.  I get that occasionally when I ride in snow. You could also try a 60 pilot and see what that does. Hope this helps. Cam.

[blueoval]

Cam, I really think it is high idle because at low speeds and quick bursts of throttle it surges about 3-4 times.  That was concerning at first and then I read the posts on surging, so I really feel that what I have is lean idle runaway.  I am experiencing something different from the surging.  It has been occasionally in the 30's when it was doing it the worse and when the temp got up to the 40's and 50's it was a little better.  I will try a richer pilot as that is what seems to be the common suggestion by those on this site that have a lot more experience than I do.  Thank you very much for the input - really appreciate all the help!  ted

[Polar-Bus]

Cam, I really think it is high idle because at low speeds and quick bursts of throttle it surges about 3-4 times.  That was concerning at first and then I read the posts on surging, so I really feel that what I have is lean idle runaway.  I am experiencing something different from the surging.  It has been occasionally in the 30's when it was doing it the worse and when the temp got up to the 40's and 50's it was a little better.  I will try a richer pilot as that is what seems to be the common suggestion by those on this site that have a lot more experience than I do.  Thank you very much for the input - really appreciate all the help!  ted

People sometimes have a misconception that when your rpm's "hang" for a short period of times, it's attributed directly to your idle circut. This may not be the case IMO. I find that a ideal or slightly lean needle clip position AND a slightly rich pilot condition will cause idle hang. When you do a long, WO throttle run you have the true opprotunity to utilize all the residual mixture left in the crankcase, when you chop the throttle, and the engine comes to a quick idle, you are still technically drawing fuel from the needle, only after several seconds are you now truly drawing fuel from the pilot circut. So my thoughts are you are ideal in the needle range, but a tad rich (causing the engine to load up, and rpm's to drop over a period of time) within the pilot circut. I run a 55 pilot in my 500 for the warmer months. Keep in mind I am NO jetting guru, these are just my "rookie" observations when playing with my jetting...

One of the things i've learned over the years of jetting, is make SINGLE circut changes, and DOCUMENT your findings. This way you can more consistantly move in a positive direction when making changes. 

[blueoval]

Is it possible to fully check the function of the KIPS system without removing the cylinder head?

[blueoval]

Thank you all so much for the help.  Really appreciate all the input and advice! 

[Friar-Tuck]

  Now that you've verified the Kips is in fact moving smoothly.
  Is there an excessive amount of play in the main Exhaust Valve ?
   (flapper pg.147 picture 92;)  don't take it out unless you want to clean it.
The mounting pins get worn and carbon bound.

  With the operating rod at rest  wiggle the ex. Valve. (flapper) up, there should not be much play there. 

   Have a peek at what the drums (Pg. 145  #'s 19 & 24 ) look like, up in the exhaust on the left and right hand side of the exhaust itself. 
     Move the rod again and look at the drums rotate, as the rod moves out away from the cyl. the drums rotate and each open a port , while the main exhaust (flapper) drops open.
   When the rod is all the way out, each drum exposes a port,and the Flapper should drop down to the floor of the exhaust flange.
     The kips bolt mod now comes into play. 
with the exhaust rod at rest, do the flats  completely close off their respective  port or do they "overrotate" and expose the edge of the port they are supposed to be cutting off.

   
  Now  go around to the hex head bolt at the opposite end of the exhaust rod on the outside of the cylinder on the "Flywheel side" of the engine.
     Break loose the Kips bolt (pg.146 fig. 83) as you remove the bolt, go back and look up in the exhaust at the drums. They will be rotating as you pull the bolt out. 
   
   The bolt mod will  close off the port and you can pick up some bottom and mid.
When you see it takes longer to explain this than to replace the bolt you will be sure to chuckle...  It's late I'm tired and if I mucked this up I'll either fix it later or just wipe it out...
    Tuck\o/

[cbxracer30]

Before you get too crazy and tear a bunch of stuff apart check the screen on your fuel shutoff , if it is dirty when your bike wot its draining the carb and the flow may not be keeping up, then once you back off the throttle it revs til the bowl fills back up. Just a thought of maybe a simple fix. CBX

[blueoval]

Thanks CBX.  I didn't think of that.  The fuel shut off is new with only 2 rides on it, but I will take a look at that later today.  Guess it wouldn't matter if it was new if there is "crap" in the tank.  I just love this site.  Such a large pool of knowledge and experience to draw from.  thx   

[blueoval]

NO high revving at all today after WOT.  Still had 2 or 3 surges when off the throttle, but the high revving was never present.

Went to a 62 on the pilot.  Loaded up a little in the tight riding, but cleaned out pretty easily, not as crisp down low, but elevation was up to 6,000 ft.  Still lost some low end from previous settings at all elevations. 

Went to 170 on the main.  At about 1000 ft and 45 degrees it went like a raped ape up top.

Same 3rd clip on the needle.  Float level as above.  32:1. 

So, excellent top end, lost some low and mid.