KX85 engine vs KX100 engine

so the problem is that it wanders up and down? or does it die? The only other thing that might be leaking is the left crank seal, but not likely. Usually if these leak, over time you will be able to see stream of residue behind the ignition cover, running out from underneath/behind the stator and flywheel.

Some bike idle smoother than others, but you ought to be able to get it decent. Usually if the pilot jet is in the ballpark it will die down/load up pretty quickly with the air screw all the way in, although it might not die instantly.

i'm pretty stumped too.

if the air screw isn't having much affect, could it be a plugged circuit in the carb? The one that has an entry in the airbox side and goes past the air screw. If this is blocked, you will get fuel through the pilot jet but not enough air to go with it. It will behave almost like having the choke on. This can get blocked if a small pc of debris enters along with the incoming air. The best way to learn about which passages go where in a carb, is to take WD40 with the red straw attached and spray it in the different orfices and see where else it squirts out. Don't wear your best shirt for this.

If this were a street bike or a bike with a vacuum port on the intake side, you could easilly test the theory by giving it more air to see if the idle picks up.

I think it's a long shot since both carbs are doing the same thing, but don't know what else to suggest. If I were there, I could help you determine if it's running rich at idle or what. Initially I misunderstood and thought it might be running erratic/lean at idle, a crank seal could do that, but now that you have explained more it sounds rich to me. Good compression, right?

sometimes that's the best thing you can do.

Over a year ago I picked up a 2001 kx85 for $200 off a buddy, the top end needed redone. After a few months of sitting I decided to tear it apart after opening up the top and I realized the piston was shot the cylinder head needed rebored and the connecting rod was heated so hot that you could see discoloring in the steel so immediately I knew I needed a new bottom end. About another month goes by account was searching online for a new or used bottom end, later I found on eBay a used/new rebuilt 2006 KX 100 bottom end for $250 bucks, as most of the motors I seen brand-new were around $570 so I decided to go with this motor on eBay.
In my manual it states a KX 85 and the 100 so based off my Assumption I figured the 2006 kx100 would fit up with my 85 top end, once the bottom end arrived I went to my local shop with my top end to have it measured for a piston, they immediately told me It needed to be re-board grrrr!!! At this point I just wanted the bike done, I purchased a new factory stock kx 85 top end jug from Kawasaki on eBay $300 and a namura piston kit. I swapped everything over from the 01 kx 85 jug to the new jug, power valve, reeds etc. I went to swap the stator plate over from the 01kx85 to the new 06kx100 and it would not fit.... This is when I found this forum to realize 2005/2006 they changed the stator plate and flywheel. I purchased on eBay a used 2008 kx 100 stator, flywheel,ignition coil, cdi box and shut off switch for $120 after putting it all together the moment of truth was about to happen...will it start, will it blow up having a 100 bottom end and a 85 top end??? I gave it a few twist of the throttle and gave it one good kick and it fired right up!!! No adjustments needed. I have about 3hrs on the motor and no problems at all!! I built this bike for my wife to learn to ride on and needless to say she is absolutely terrified to ride it after watching me ride it I'm a 31yo 180lbs and this bike pulls me no matter where I want to take the bike, hill climbs, local race track, in the sand, no matter what this bike out performs beyond what I thought it would!! No other mods have been done to the bike, all 100% 01kx 85 besides the bottom end and electrical system. For a you kx builders I hope this has helped you out.

motometal said:

The 420 chain was a weak spot on the little KXs I had, put a 428 Renthal kit on and it still wore out fast (at least the chain is cheap), do the new ones come with a 428 yet?

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Almost 10 years later they are still using the 420...
I just picked up the only 428 sprockets I could find, still currently made by JT Sprockets, and an RKGB428MXZ-124. A big weight penalty, but should be much more durable.

flyinzuki said:

Almost 10 years later they are still using the 420...
I just picked up the only 428 sprockets I could find, still currently made by JT Sprockets, and an RKGB428MXZ-124. A big weight penalty, but should be much more durable.

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Check out "bearing belt and chain" they are out of Chico California and have a large bulk supply of chain and sprockets.