2000 KX250 Kickstarter Kicking Back Really Bad!

[Kmiller2723]

So I bought a 2000 KX250 that wasn’t running and had a sheared off kickstart shaft. The previous owner said he had a lot of electrical work done on the bike and said that he rode it once and sheared the kickstart shaft and couldn’t bump start the bike.

 

I tore the bike down completely and found the big end bearing took a dump. Which I figured was what caused the kickshaft to shear. So I rebuilt the entire motor. New crank and transmission bearings. New hot rod crank, standard compression vertex piston, and all new gaskets. Everything was torqued to the manual specs.

 

I have got the bike to run but like every other time I kick it over the kickstart will kick back ungodly hard. It has ruined a pair of sneakers, Carolina work boots, and almost put a hole in my aplinestar riding boots. Along with leaving my foot pretty black and blue. I’ve owned numerous 250 two strokes, ktm 380, and a CR500 that didn’t even come close to this thing.

 

What I have checked:

 

1. Stator timing marks are aligned

2. Flywheel is aligned with woodruff key on crank

3. Kickstarter ratchet punch marks are aligned (new shaft)

4. Have tried a different CDI box

 

So Ive looked around the internet and have found people with similar problems but no one seems to have a solution. The new kickshaft splines have twisted and there is gaps where it’s starting to separate from the shaft. Which I have installed yet another shaft and it has done the same thing. So I did bump start the bike today and it ran good, but I could not get it started again after that.

 

Sorry for writing a book but Just want to be thorough. So I’m at a loss, if you guys have any input I would greatly appreciate it!

 

Thanks in advance.

 

[broken.biker]

Sounds like an issue with timing. I had a similar issue a year ago. The timing mark might be perfectly lined up but there are a few things that can cause the timing to be retarded aside from the pickup angle.
I'd start by checking the 'arms' (are they called arms) that go around the magneto. They are supposed to be a set distance from the magneto and any further away retards them and further in advances them I beleive, but I am not sure. All I know is moving it one way does one thing and the opposite does the other. It has to do with lens law. Electro magnetism has never been something I have understood well. Hopefully your manual has a spec for the gap. For my kx it was the width of a piece of paper. Also my arms had loosened until they were dragging on the magneto leaving a pit in it so I had to replace it before I set the gap.

The other thing that could cause it is putting your piston in backwards. All semi-modern to modern pistons are actually not round but more oval shaped. The shape is known as the piston profile. Don't believe me, take a modern piston, lie it on its side and nake it slowly roll on a llevel table and you will see it does not roll uniformly. If your piston has some sort of mark or arrow that needs to point toward the exhaust (conventionally). This is because the forces on the piston are not uniform in its reciprocation. They are ovals because horizontal components are introduced when the conrod is not verticle which is most of the time. Additionally one side of the piston should be different than the other because when combustion occurs there should be a slight x+ (crank to exhaust is +) component and it needs to not have the rings bind up or grab. Also in race engines the different shape has another purpose: to throw the engine in the right direction. This lets you retard your timing until it is very close to TDC and get a little "push" in the right direction. Now your timing would have to be very close to TDC for this to have a significant effect during normal operation, but when you are kicking it it spins 1-2 times. It is spinning slow enough that this can cause it to backfire. A good indicator of this is if the engine runs completely fine once started.

It would also help to double check the timing.

[broken.biker]

Sorry made a fool of myself. In a proper engine spark occurs before TDC for normal gas. Since gas takes time to ignite. The idea is that the chamber is rapidly building pressure when the cylinder volume is at its minimum (TDC).

Also here is an good article on piston profile for anyone interested.
http://blog.wiseco.com/pistons-arent-round-profile-and-ovality-explained

[Kmiller2723]

Thank you for the reply broken.biker!

Good info on the piston! I actually just read an article about that in MXA or Dirt Bike Magazine!

However I do believe I have the piston installed correctly. The arrow on top is pointing towards the exhaust port and the window on the piston is on the intake side. The rings were aligned with the pins in the piston ring grooves. So I don’t believe that to be the issue.

Now when you are referring to “arms” around the magneto are you talking about the pick up coil? Because there is an “air gap” that needs to be set between the flywheel and the pick up coil that I was going to check and set today.

[Kmiller2723]

So small update, got the air gap set on the pick up coil, but didn’t fix the problem. Bump started it again and it ran good, however when I would pull the clutch in it would idle up some on its own. Also if I was in first gear it would run without giving it gas and the clutch out.

 

So now I’m thinking possible air leak or float level not adjusted correctly. But would either of those issues cause the kickstarter to kick back hard?

 

Well either way this weekend I’m gonna strip the bike down go over everything in the carb, check throttle cable routing and do a compression test on it.

 

Any other suggestions on what to check or look for while I got her apart would be appreciated!

 

 

[broken.biker]

Yes that is what I am refering to. The manual for my bike called them coil arms since they stuck out and wrapped around the magnetto. Also sometimes magnettos wear out due to vibration its more common on early CDI units. You would have bad spark though. Are there any other symptoms you've noticed? The magnetto has a few different jobs. It induces current in the pickup coils, it 'times' the spark, all while 'hopefully' not magnetizing the crank. Id also check the warfarin key. If that is damaged or missing then it can let the magnetto slip.

[broken.biker]

An easy way to check for air leaks is to have the bike idling and spray something flamable aerosal around areas you thing are leaking. If it alters the way the engine runs such as throttling up then you have an air leak. Have you checked the reeds?

[Kmiller2723]

Checked the reeds and there was no chips, or frays in the pedals and could not see any day light through them. Also installed a new boot on the reed cage as the old one was cracked and dry rotted.

[broken.biker]

Have you tried advancing the timing slightly to see if it starts or runs better? Also what fuel and additives are you using? Different fuels and mixes ignite at different rates that is why spark occurs BTDC if it lit completely instantly it would happen at TDC. You could be running a fuel with too high an octane (or numerous other fuel properties could be wrong). You wouldnt happen to be using some sort of racing fuel with very high combustability?

Btw what you described 2 posts ago sounds like it could be a clutch that is out of adjustment or scored. It is normal for the engine to rev up slightly when you pull in the clutch while moving in neutral on a carburated bike. Though the pulling forward with the clutch pulled in sounds like scored or OOA. My kx and my old crf both dod that and to an extent it is normal that it is normal for a lot of bikes since the clutch just stops pushing the plates together and sometimes due to grooves or a bad adjustment or even just design they arent completely disengaged but they disengage enough that not enough power is transmitted to cause the bike to move. Now on a motocrosser I never particularly cared about this slight pull since there are no traffic lights or stop signs on a track. But if it is making the bike creep and putting on tbe brakes stalls it then I decide it is time to adjust it. But I am not anal retentive on clutch maintainence, its not a car, changing the clutch is simple.

Im working on writing less long posts. But I also writting a book. I write too mucj here and too little there.

[Greenwrench]

Sounds to me like it something is going on with your spark timing causing it to kick back on you I think your on the right track with the stator /pickup coil . Have you tested it with a meter ? You said the previous owner did alot of electrical work that should be a huge red flag right there what exactly does that mean ? The electrical system is pretty simple and if you have already tried a CDI and are pretty confident the timing marks are good I'd be inclined to think the pickup itself or half your stator might be going out you can test each part of it  individually . 

[Kmiller2723]

So we tried retarding the timing on the stator and still had the same results. Also ran a compression test and it maxed at 150psi. So haven’t made much progress.

Does anyone know what’s up with the different flywheels offered for the 00 KX250? I will post a picture of the fiche diagram.


You can see in the lower right that they offered an option flywheel. The bike currently has the style that is on the right side. I didn’t know if anyone knew what the difference was and if it maybe part of my problem?

[kxrob]

my gas gas 280 trials bike was doing this ( kicking back) when the pilot and choke jet was lean . so lean condition , i would look for air leaks ( did you tighten the carb hose clamps on the reed side up ?

[KDXGarage]

The different flywheels are heavier or lighter.

[Kmiller2723]

So tore the bike back down and here is my findings.

Electrical.

Stator and pick up coil were with in the resistance specs

Primary and secondary windings on the ignition coil where in the resistance specs.

Voltage regulator was with in the resistance specs.

Fmf fatty and turbine core had a pretty decent gap where they meet. So I fitted the stock exhaust and has a tight fit where they meet.

Checked the reeds. Which gaskets, reeds, and boot all looked good.

Checked in the cylinder on the exhaust and intake port and everything looked good.

Timing is lined up according to the manual and when I removed the fly wheel it was still on the woodruff key.

Air gap was also set on the pick up coil according to the manual.

I did find some unusual jetting going on though.

Stock

Main-158
Pilot- 52
Needle- N3WE
Clip- 3rd notch from top

Currently in the bike

Main- 155
Pilot- 62
Needle- N3WE
Clip- 2 notch from top

Now I have never seen someone go up that large on the pilot jet. So maybe the culprit?

Spark plug

Ngk br7es

So what I am going to do is get a carb rebuild and go back to stock with everything. Plus a new choke plunger as the current one is a little finicky. Get the recommended spark plug and a new woodruff key for good measure.

Also on the pick up coil it looks like the fly wheel kissed it at one point and shaved a little of it off. Would this pose a problem if it tested ok?

Picture show damage

[kxrob]

Good start for the pilot is a 45

dependimg on your temps and elevation 

either a nedj or necj Suzuki needle really cleans up the jetting 

158 main is fine

[Kmiller2723]

Thanks kxrob for the input! I just ordered a carb rebuild kit and new choke plunger. So I’m just going to get it back to stock for the time being for a base line and adjust from there. My main concern is just resolving this issue with it kicking back. So I’m hoping with eliminating the massive pilot jet and the gap between the expansion chamber and muffler will cure that problem. I’m also installing a new woodruff key for good measure. If those two things don’t work I’m kind of out of ideas.....

[Kmiller2723]

Alright guys, so made all the changes as mentioned above and now it’s worse than before. Bike still kicks back and now I’m pretty sure when trying to bump start it, it is trying to run backwards.

So I am not the most savvy person on the electronics part of a dirt bike, so please help educate me.

So with what’s going on I have a feeling there is a short in the stator, or pick up coil. It’s the only electrical piece that was moved before the problem got worse. So am I correct in my thinking or does the regulator, ignition coil, or CDI have any bearing on the timing? Also if one of these components are bad will it take out one or the other components?

Sorry but if someone could explain how each component functions exactly and what to look for and test would be greatly appreciated!

[RodrigoVieira]

Hello my friend. 

The same is happening with my fresh rebuild 2000 kx250. 

Did you figured out what was the problem?

Thanks in advance