Jump to content

kx450f kicks really hard andthen stops

Recommended Posts

my buddy has a kx450 think its a 08 anyway we checked the valves and they needed adjusting.timing is right on the money and tried to start it up and when i kick it over it kicks really hard where irt will stop and you have tu puch really hard to get it to move.it did this before we adjusted the valves so we thought the valve clearance was the isue.the bike has been starting hard anyways.

Share this post


Link to post
Share on other sites

Sounds like your auto compression release is not adjusted correctly, or not functioning. I suggest checking it.

CoKTM

Share this post


Link to post
Share on other sites

Quick question,

Did you adjust those valves?

If you did, you may have measured wrong and made the exhaust clearance too large, making the auto-decompression, now ineffective. If, as you said, it was always hard to start, it may have been out of time then, or you just have a worn decompression pin on the auto-decompression stem.

If you did not adjust them, then as said above, something is now out of whack with the decompression system (lost spring/s?) or an actual timing jump while you worked on the valve adjustments. The hard kick is usually always indicative of bad timing (even one notch out). Even if you line up, you should always count the actual timing chain pins backwards to the intake cam (spec is in service manual) AFTER timing the exhaust cam with all markers, then count back, this way, when the cam tensioner is reinstalled, timing remains right, also, is, or was the tensioner backed out and reinstalled properly? this can cause a jump or slack chain on first kick as well after valve work. This will make the engine way out of time. If it is hard to kick, always STOP and inspect. So you dont tap and bend a valve. Never keep going with a hard kicking four stroke. Hard starting is one thing, a very hard kick over is another.

Share this post


Link to post
Share on other sites

how do you adjust the decompresioner the spring was missing.it does not look like its adjustable or is it.the valves are the proper clearance.

Share this post


Link to post
Share on other sites

You don't adjust the spring. It sounds to me like the spring is either missing or the weights are stuck open. Look at the end of the exhaust cam and let us know what you see.

Share this post


Link to post
Share on other sites
spring was mising and now it won start all new top end marks line up no go.

Sorry, I misunderstood one of your posts. So is it still hard to kick? If so, take out the spark plug and remove the valve cover. Watch all things go around. You are looking for the exhaust decompression pin to do its job. If it is not lifting the valve off its seat there's your problem. (You can remove the exhaust cam and work the entire assembly, see how it works and you will find the problem.) If it is you can double and triple check the mechanical timing. Make sure you are turning the balance shaft in the proper direction of rotation. If still no problem found you can remove the head pipe and carb. to look at the valves or just measure the gap between the bucket and the cam lobe, that will tell you if something is bent.

Share this post


Link to post
Share on other sites
Sorry, I misunderstood one of your posts. So is it still hard to kick? If so, take out the spark plug and remove the valve cover. Watch all things go around. You are looking for the exhaust decompression pin to do its job. If it is not lifting the valve off its seat there's your problem. (You can remove the exhaust cam and work the entire assembly, see how it works and you will find the problem.) If it is you can double and triple check the mechanical timing. Make sure you are turning the balance shaft in the proper direction of rotation. If still no problem found you can remove the head pipe and carb. to look at the valves or just measure the gap between the bucket and the cam lobe, that will tell you if something is bent.

The bold above is very important in timing the KX. The correct way to rotate the balancer shaft is counter clockwise. I know from experience lol :thumbsup:

  • Like 1

Share this post


Link to post
Share on other sites

i hate to revive this thread but im in the same exact situation as thecount. i currently have my bike stripped and the valve cover off. i see no sign of abnormal wear but i cant get the kickstarter to even move.

any ideas??

Share this post


Link to post
Share on other sites

sounds like you dropped a valve. Will it go one way then stop, then back the other way then stop in the same spot or close to? if it stops in the same general area then you need to pull the head.

Share this post


Link to post
Share on other sites

i mean nothing in the head will even roll over.

it use to just do this..... not kick, not kick, kick and not start. then repeat.

now it wont even kick.

i have no clue

Share this post


Link to post
Share on other sites

Take the valve cover off and the balance shaft cover cap off. Use the balance shaft to turn the engine and inspect while you are turning it with the balance shaft. If it will not turn with the balance shaft you will need to start your disassembly process until it does turn over and you will find your problem. It could be the bottom end broke. Main bearings failing with the symptoms you are describing are common on these bikes.

Share this post


Link to post
Share on other sites

ok so i know im reviving this thread but i had some time to actually look at the bike today.

the motor turns over now that the cam tensioner is off.

i also have the valve cover off and am going to check the valves. but why was it locked up before i took off the tensioner?

Share this post


Link to post
Share on other sites

Its possible you didnt reset it when you took it off last?

To me it sounds like a classic case of the tensioner was put in right last time.

Share this post


Link to post
Share on other sites

well i take that back. the motor spins one way and stops, then the other way and stops around same place.

dropped valve?

if so where do i even start at fixing that lol

Share this post


Link to post
Share on other sites

My bike did something similar. It started fine then 5 min later when I kicked it the kick starter would not even go all the way down. Took to the dealership and' my timing chain skipped a tooth. They can stretch like a drive chain I guess. They re set timing and it ran fine had nothing to do with valves. Hope that helps Cuz my first thought was valves too.

Share this post


Link to post
Share on other sites

I was going to say check timing, but you said it was timed correctly. Mine has jumped time twice. Makes it very hard to turn over. I suggest replacing your timing chain asap.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×