JohnF

Member
Jul 21, 2007
35
0
Just got me a '97 KX100 and its not running right. When I got it, it had some weird spark plug in it and would barely run. So I put in a BR8ES and it runs alot better, starts first kick but it seems like its never in the powerband, wont spin the tire or pull a wheelie even in first. And it seems like there is a rev limiter but its not at that high of an rpm. But there is a probably 500rpm time frame in each gear where the bike pulls pretty hard - slow, fast, and the slow again. for that split second it seems like thats how the bike should always run. Where should I start? Clean the carb, different plug, what?

I was told the bike has been sitting for a month but it has less than 30min since full rebuild -crank and bearings, piston, etc plus it has new stator and clutch. Its in good shape and has some other new parts, Once I get it running right it seems like it would be a really fun bike to screw around on. Should be pretty fast? I topped it out at 55mph today and I could tell it was just about reacing max rpm.

So Im just looking for a place to start, Im sure its something simple. What plug should I be using, and also what mix ratio - 32:1? Any help will be greatly appreciated, would like to go riding tomorow. Thanks!
 
Jan 3, 2007
1,860
0
JohnF, it sounds like you need to clean the carb and mabe buy one size bigger and smaller main jets, and pilot jets, and then play with jetting the bike properly. Then the bike should spin the rear tire and catwalk really nice. Also, the spark plug is the right one and 32:1 will work well in the bike after you jet the carb properly. This will help you jet your carb, http://justkdx.dirtrider.net/
Then go to tech tips on the left and then go to engine hop ups and finally to carb tunning. Have fun.
 

j.lawson

Member
Jul 18, 2007
78
0
yeah man, and dont just go throwing any plug in your bike. Assuming you dont already know this, if that plug is to long the carb. will be the least of your worries. Get a manual or call a shop and get the right plug. That plug is an NGK you got in it, I run B8ES in my rm 125...
 

griffbones

Member
Sep 12, 2006
329
1
Run a compression test, check the reeds, make sure the silencer isn't pluged, if this bike has a power valve (not sure if that year had one yet) make sure it isn't broken or stuck.
 

tyler_43

Member
Jun 22, 2007
126
0
i run a BR9ES plug in my kx100... a BR8ES (NGK-R) or B8ES (NGK) are slightly hotter but I'm sure they'd work fine. As for the power issue, I'd fiddle with jetting and see if that helps. While you have the carburetor off undo the reed cage and make sure they aren't all mangled. If that doesn't work I'd check the powervalve... If it was stuck you'd still have good high rpm power but hardly any low end (like a yz80 :P). Oh, and they said it only had 30mins on it? After i rebuild (or even put a top end) in my bike i usually run a tank or two of gas through only riding at about 50% load in order to break it in, that way the rings seat properly. I'm sure that's overkill but according to our local Kawasaki dealer you should always give a bike a "break-in run".
 

JohnF

Member
Jul 21, 2007
35
0
ok i cleaned the air filter, checked the reeds and they look brand new, and it has good compression.

the bike really runs like crap, it starts up first kick though ussually. its got no power, no wheelies, no spinning of the tire. but once in a while ill feel it pull good for a split second at high rpm. most of all it sounds horrible, not smooth at all.

oh and also I just found out its a KX80, would that require a different spark plug? Im pretty pissed I know this guy lied to me, he also said it ran perfect and just needed a new spark plug thats why it ran bad when I got it. If I dont get this thing running good without spending alot of money Im gunna have to burn the guys house down

im gunna go take the silencer off and see if its plugged
 

oldguy

Always Broken
Dec 26, 1999
9,419
0
I would now be very leery of the 30 minutes on a topend rebuild. If the guy passed off a KX80 as a KX100 he probably saw he had you foolsnagged pretty good and set the hook alll the way.
You are going to need to do a compression test which should tell you if the piston and rings are any good.
The lack of power is either that or the jetting is way off. You also need to pull the carb and be sure every opening is clear of obstructions best bet is to blow each one out.
Good luck and keep in mind if you can do it yourself it won't be a bank breaker- at least you are not repairing a 4 stroke
 

JohnF

Member
Jul 21, 2007
35
0
the carb is cleaned for sure, i do think however i need to adjust the float level. i ran out of gas yesterday and leaned it on its side to fill the bowl back up and when i started it, it took off like it should through 1st and second and then went back to ussuall. so i think its not getting enough fuel. but then i was running out of gas again in 5th gear and it ran like a bandit through the top of 6th and then it was out of gas. i know bikes run faster when theyre leaning out (i know its bad) so then i thought maybe its getting too much fuel.

i guess it could be jetted wrong but I think it would have to be way off to run this bad. what size should the jets be? ill check them to see if they are the right ones but i dont think its the problem.

ill take a video of it tommorow and show you all how it runs. its not that its just always slow, its that it runs like crap and then for a second it will move ok. Running rough is the best way I can describe it. I would think if the compression was bad it would be more consistant and just always slow, but its really unpredictable how its gunna run. from kicking it, it feels like the compression is really good but ill check it with the gauge.

so....

carb is clean
air filter is clean
exhaust is not plugged
spark plug is good
reeds look brand new
compression seems really good
fresh gas

possibly the float level needs to be adjusted....how do i do that?
 

JohnF

Member
Jul 21, 2007
35
0
and on another subject....would it be possible to fit a kx125 motor in here? it looks like its already pretty cramped, just wondering how much physically bigger the 125 motor is. i can weld and fabricated no prob btw, but i dont want to cut the bottom of the frame out to accomidate a taller motor and then make lower rails
 
May 5, 2007
102
0
I would think its the clutch.If it had low compression itd be hard to start.If it had bad gas itd be hard to start.If it had a clogged carb it would pick up then bog hard and not pull at all during the bog.But if the clutch is slipping then it would get the rpms but none of the power to the wheel.But im no expert and im not sue if a manual clutch can even slip.But it seems like itd be a clutch issue to me.Unless its bogging and not pulling at all i really would think its a clutch issue.Some one more knowlageable please correct me if im wrong.Hope i helped.
 
Jan 3, 2007
1,860
0
derek the 2 stroke, man your awsome. I never thought about it but that would make a good deal of scence. Take a look at the clutch and see if the basket is grooved abd if so then time for a new one.
 

JohnF

Member
Jul 21, 2007
35
0
noooo, the clutch is new. i can tell its good, you rev it up in first, dump it and it barley spins the tire in dirt and it bogs down. if it was the clutch it would just rev and not spin the tire at all. i know when a clutch is bad i have replaced many, this isnt the problem. the bike runs like crap
 

JohnF

Member
Jul 21, 2007
35
0
can someone please tell me the correct distance between the bottom of the float and the float bowl mating surface for a KX80?
 

JohnF

Member
Jul 21, 2007
35
0
I rode it just now and for some reason it runs good and the powerband is there for sure, i can shift through all the gears fine and move along pretty good. But the bottom end is absoulutly dead, and i can rev it up all the way in 1st and dump it and it will barely spin the tire
 

JohnF

Member
Jul 21, 2007
35
0
yeah, i have just about narrowed it down to the carb

someone please tell me the correct float level and what jets are supposed to be in there. then i can fix it
 
May 5, 2007
102
0
JohnF said:
I rode it just now and for some reason it runs good and the powerband is there for sure, i can shift through all the gears fine and move along pretty good. But the bottom end is absoulutly dead, and i can rev it up all the way in 1st and dump it and it will barely spin the tire
If its revving in nuetral and when you dump it its bogging i would think is a pison or rings issue.Im not sure though like i said im not an expert.Is it revving or not revving.If its bogging its not the clutch.If its not bogging then i would think there was a problem with getting the power to the wheels.are you sure its got good compression?When i had my old 89 yz 80 its cylinder was in bad shape.It had similar problems to your bike.I think you should take a look at the piston and rings and cylinder.But im not sure,again if im wrong some one more knowlageable please correct me.
How do you know the compression is good?Can you kick it over easily?
 
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JohnF

Member
Jul 21, 2007
35
0
i can start it easily, maybe because Im way too big for this bike and im used to kicking the 250's. but for only 80cc's it seems like the compression is good, i can slowly turn it over by hand and got to put some weight into in. but one swift kick and it fires right up.
 

JohnF

Member
Jul 21, 2007
35
0
maybe ill take the head off, i dont want to take the cylinder off because i dont have a ring compressor to get the piston back in. and im not good at squeezing it with my fingers. maybe its easy on an 80cc, last piston i tried squeezing in was my 660 raptor that was borred out, i had to borrow a ring compressor for that thing
 

DougRoost

~SPONSOR~
May 3, 2001
720
0
Don't pull the head just yet. Start with a compression check using a compression gauge. If you don't have one you probably should since they're not expensive and can tell you a lot about any engine. I'd bet you could probably do the rent-for-free deal at Autozone and get a reading of just where you're at.

This sounds like a classic 2 stroke fuel/jetting issue. You may even have an air leak somewhere but my guess is indeed float level or jetting.

If you want the peace of mind of a quick peek iniside your cylinder, simply pull the pipe and shine a light in there. You'll be able to see that side of the piston as well as get a pretty good look around the cylinder.
 
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