05 KX85 Lean stumble

My sons 2005 KX85 has a lean stumble (bog) if the throttle is whacked open really fast while the bike is idling on a stand. Also if my son wacks the throttle wide open real fast from a very low speed like 1 or 2 mph (again from idle speed), the bike goes into a bog, it will not die and will not accelerate, it just stays in a bog until he lets off of the throttle and then rolls into it again. I have been back to my Kawasaki dealer where we recently purchased this left over 2005 model, they tell me all of the KX's will lean stumble if you wack them wide open real fast from an idle, or from an all most stalled speed while riding. They said even the KX250 will do this too! Now we just sold a 2003 KX85 and I don't remember this bike doing this or at least not this bad. The two bikes appear to be identicle other than the Wiseco Pro Lite piston that was in our old 2003 KX. I have tried changing the jetting on the pilot circuit but it does not get rid of this problem. With stock jetting (45 pilot, needle third groove, 140 main, air screw 13/8 - 1 1/2 turns out)(at 800-1000 ft above sea level and 75-85 degree temps) the plug looks pretty good, and this same carb with the same jetting worked good on our old 2003 KX85. If I ride the bike (I weigh 185lbs)and get rolling slowly and then wack the bike wide open it will bring the front wheel up in 1st, and if I keep it in the powerband it will wheelie in 2nd, 3rd and sometimnes 4th gears without even trying, so the bike has plenty of power. Does this lean bog or stumble sound normal to any other KX 85 owners? BTW I have also looked over the reeds (they look fine) I have tried going up one with the pilot jet (did not help) I tried raising the needle one groove(did not help) and in fact the bike over all seems to run best with the stock carb configuration mentioned above. The only thing that will completely get rid of the stumble is if I turn the air screw almost all of the way in, but then this just turns the plug black instantly and the bike runs horible except for the stumble being gone when wacking the throttle wide open real fast from an idle speed. Am I just too picky or is this a real problem? I know my son needs to learn to keep it up on the pipe and not wack it wide open from an almost stalled speed, but he is just 10 years old and just learning for the most part.

Chili said:

You should be able to jet that out of the equation. You said you went one leaner on the pilot and clip, is something keeping you from going leaner?

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I went one step richer with both the needle and the pilot jet, but it did not help. I sure don't want to lean it anymore. Actually I am back to all stock jetting as overall this seems to be where the bike runs best. I think the pilot is close to being correct because I get the highest idle at about 1 3/8 to 1 1/2 turns out with the air screw. The bike idles great and if I take off normally letting out the clutch and then wack it wide open real fast after I get rolling a little bit it runs great. This thing just doesn't seem to like being wacked wide open real fast from an idle speed.
Could the Wiseco piston in our old 2003 KX85 make that much of a difference due to the lighter weight and slightly different port design of the Wiseco?

Chili said:

Is it a definite bog sound? Our last KX80 didn't bog when whacked open but stumbled and gurgled until it cleared out and got going. The cure was several steps leaner on the pilot and one up on the clip.

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It is for sure a bog. As I stated before, by shutting down the air screw and making the bike super rich the bog goes away. I am starting to think that there is something else going on and by shutting down the air screw it masks another problem. Our last KX was identicle to this bike and we are using the same fuel and oil and mix ratio. In fact before I got the other bike sold I had filled both bikes from the same batch of gas and the other bike with the same jetting ran great! I wish I would have kept the other bike it ran really nice and I have been fighting this new bike for about two months now, I am getting sick of this bike!
I am begining to wonder if the head gasket is seeping water into the cylinder or somthing wierd like that, the silencer sure seems to get wet at the outlet, not just oily. But have not really noticed the water level in the radiator dropping any. But I did just change out the antifreeze for some engine ice yesterday and I seem to be getting some air bubbles in the radiator and I can't seem to get rid of them by bleeding the head or letting it run with the cap off. Makes me really wonder if I have had a head gasket seeping the whole time, this would sure cause a bad throttle response! I haven't really noticed anymore smoke from the bike though. It smokes pretty good when you first take off after warming it up, but once you run it through the gears a couple of times it pretty much quits smoking all together, so?

breezeair said:

My son 06 kx85 has a little stumble just off of idle but only from standing still and really giving the throttle a wack. When he is riding it is not happening. We have installed power reeds, 45 pilot, 138 main, NAPF needle 3rd pos. The bike is still a little rich when he is not on pipe but he never fouls a plug and he does not complain.

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I see you have went one step leaner on the main and needle but where are you setting the air screw approximately, and what altitude are you at? Also are you using Boysen two stage power reeds in the stock cage? I tried those reeds on my sons old CR60, I guess they worked ok but I couldn't really tell the difference in power or throttle response for some reason, but I did have to lean all circuits out after installing those reeds. Did the reeds make a noticeable difference in your KX85?

BTW thanks for the help guys! :cool:

I talked to Eric Gorr yesterday, and he also thinks this bike most deffinetly has a lean stumble, but he is not sure why. He doesn't think that I have a vacuum leak because it returns to idle ok and it has been this way for two months and has not yet siezed, and my plug looks tan. I told him that raising the needle didn't help and neither did going up one size on the pilot, so he suggested that I try a one step richer throttle valve. It just seems strange that I am having this problem when other KX's don't seem to have this issue, and our old 2003 didn't have this problem either, it ran great! BTW- Sudco wants over $65 for a throttle valve that I am not even sure will help. :(

I just had a thought, this bike has had this problem since day one, so I know the power valve could not have been gummed up the first day! But is it possible that something inside the power valve chamber was install wrong at the factory? The accuator shaft's index dot is lined up with the mark on the side cover where it is supposed to be. And it does move forward (advances) when the bike revs up (checked this while riding the bike). It would really blow to have to pull the whole top end off just to look at the power valve assembly, just to find nothing wrong. But I am (and so is everyone else that I know) running out of ideas to check out on this bike.
Bike revs up slower than our 2003 KX, and if the throttle is wacked open very fast at all from an idle speed or from a really slow riding speed it has a very bad Bog! Yet if I do the Eric Gorr 1/4 - 1/2 throttle test, ie. while riding in second or third gear in a circle and slowly open the throttle from 1/4 - 1/2 twist, it revs just fine. ?????

The only time I get any spooge at the silencer is when I ride the bike hard for a while. So I do think the main is a little fat no doubt, maybe the needle too. But with my son's fairly easy riding I get no spooge at our current temps. I really think that there has to be a mechanical problem behind this because our 2003 was stock jetting and it was most definetly rich and had spooge out the silencer, but it did run strong. I just never got around to tuning it before I sold it and bought this new bike.

When I say this thing bogs, I mean severe bog! This doesn't seem like a simple one size off on the jetting type issue, and it is strange since all the KX's are well known for being jetted too rich, yet I have this severe lean bog?

BTW- thanks for the input Husabutt

Well tonight I came very very close to taking a hammer and knocking the cylinder clean off of this piece of crap, so I guess it is time to sell it and move on! :|
I test rode a CR85R, what a bike! The Kawi pales in comparison to the Honda, the CR had great throttle response and had way more power too! I probably won't be able to buy my son another bike until after the first of the year, but I am strongly considering the Honda, that is if any of the dealers have any of them left after the first of the year. I sure hate to see the beloved 2T's go. :(