Idle Kick-Backs v.II

[kawdude]

I recently went thru and rebuilt the KX engine from top to bottom.  Fired her up today and it really runs good except for the infamous idle kick backs, surges, popping...whatever you want to call it.

To research this issue I have done numerous searches that have yielded excellent info but the following lays it out well.

In reading the following post...
http://www.pitbull-racing.com/index.php
name=PNphpBB2&file=viewtopic&t=375

I have impression that switching out the carb seems to fix the problem.  I did that and the problem is still there after the rebuild which surprises me.  I would have thought something would be different with this issue.

Currently jetting is 168m, 55s, needle on middle clip.  Seals are brand new.  No air leaks that I can tell.  I have attempted some of the mentioned fixes on top of switching out the carb but nothing seems to make it better or worse but at least the bike actually idles.

Has anyone else suffered the same and found any other solutions?

[Woody223]

What do your reeds look like?

I had a similar problem on my KX5 and the reeds were a little worn, they did not close all the way as they were old and starting to get brittle. I changed from fiberglass Boyensen reeds to carbon fiber and it helped alot. Most of the surging is now gone but it takes a little more time to "pick up" than it did with the glass reeds.

Woody223

[gowen]

I switched to c12 fuel instead of 93 pump and it fixed about 80% of the the poping and 100% of the surging.

[kawdude]

Originally the problem started or was intensified  when I added a Steahly and moose space at the same time last year.

[kawdude]

Why would changing the fuel help?  Different O2 level???

[kawdude]

Can someone describe how to tell if the bike is running rich or lean?  I know this is lame question but I can't tell by the sound.

[fast500#12]

when it is running rich it will smoke more than usuall and some times depending how rich it will hesitate when you goose the throttle. when it's lean you will have higher than normal operating temps and some times get what i like to call run away idle, when your bike is idling really high and doesn't like to shut down with the kill switch. this is intensified by the higher engine temp. also when its rich you get the squirt gun effect if its really rich, lots of black oily spatter out of the scilencer. there are other ways of telling these are just the ones that i know and love.

[kawdude]

Let me throw out what it sounds like...
When I first reassembled bike ran rough up to mid and wouldn't idle.  From mid on ran smooth...smooth whine with lots of snap.  Next time I rode the smooth even whine at mid and beyond is gone.  Rough sound.  I don't know how to describe it.  Doesn't sound pingy but I don't really no what that would sound like.  Power is still there but not snappy.  I can't say it bogs either.  I don't notice splooge anywhere.

[mikesmith]

If its rich it will "blubber" is how I like to describe it,it wont sound crisp or have much pull/acceleration or cut out down low.The plug will be black,wet or foul and as mentioned above wet exahust.If its lean the idle or even holding a low throttle the engine will idle up and down on its own, the bike will ping and run hot.Jetting is something you need to work on to see what works and what doesnt,take notes.Weather temp,humidity,altitude,fuel and mods done to the bike effect jetting,so if you write it down for what works on what type of conditions it makes future jetting easier.Your owners manual has this information in it that would help make it easier,or let us know how it goes.

[kawdude]

Thanks guys.  I would say the bike is rich because is the lean descriptors you mention aren't happening.  I'll look at the plug.  The bike doesn't load up or cut out down low and doesn't appear to be splooging.  Currently jetted at 168m, 58p, and the clip is on the 3 position.  Would it safe to raise the clip to lean it?

[mikesmith]

Try it,just do a SHORT ride and check the plug,Itll ping if its to lean and to rich wont hurt it.I know with my bikes jetting it effects my gas mileage and power a lot,so I like to keep it jetted as close as I can, so trying differnt things is part of it.Dont forget the air screw adjustment.

[Twist-a-grip]

Take and mark your throttle in 1/4 increments.  These carbs you have to jet according to throttle position to make sure you are tuning to proper ciruit.  I usually start at the main(full throttle). I then go down and get the bottom set,idle-@1/4throttle(pilot/air screw ).  All that is left is tuning the midrange(needle).
Each area the motor will tell you what it wants, give it what it wants.  I like to start rich and gradually lean it until it just cleans out.  It will blubber and hesitate if it is too rich and acceleration will be poor.  Too lean and the engine will lose power, run hotter than normal and make what I call a crackling sound.  Once you get it all tied together your power will be seamless with no notable change from one circuit to the next.

[kawdude]

Okay, this is what I've done so far.  The bike is rich (I think).  Plug is black and splooge coming out the rear.  
1. Replaced reeds with Boy Power Reeds.  Hopefully to cure hard starting.  
2. Dropped slowjet to 55 from 58.  
3. Moved clip up to 2nd position since it appears rich.  May go to the 4th position to see what happens since what I'm hearing may be pinging.
>>Bike Idles .  

When I started the bike the first time since making these changes the bike started and bogged and died.   This happened twice.  It was dripping gas on the floor...not much but some.  After getting it started, the bike still appears rich.  No bog but just runs rough seemingly all thru the range.  This is more noticeable after midthrottle.  Unfortunately, wasn't the best day to do this work.  Cold and rainy.  Wouldn't the cold lean the mix?  

Also, In playing with air screw I can't say that it changed anything.  If I turned it right (IN) the bike would try to die if not saved by a quick rev but going the other way didn't seem to make a difference.  For my area I can't believe that I need a 52...

[Folke]

Dont change slow jet to 52, not under 55.
Check silencer so the inner pipe not is broken.

[kawdude]

Dont change slow jet to 52, not under 55.
Check silencer so the inner pipe not is broken.

Why not?

I also noticed that the slide in this carb is stamped "7".  Isn't the standard 6