400ex timing question

[AtvKid4Eva]

hey guys it seems like no matter what i do on my 400ex when i try and set the timing the cam marks are aligned perfect with the cylinder until i install the tensioner and then it seems to either throw the timing off a tooth either way..so can someone give me some clarification on what i am doing wrong? the bike wants to start but wont im assuming the timing is slightly off. i made sure the "T" is ligned up and i positioned the cam lobes down..ive set the timing before on a 400ex but javent ever had this hard of a time keeping the cam markings ligned up after installing the tensioner. thanks -Bobby

[CJM]

Install tensioner, retime.

its that simple really. Your saying your timing it then putting on the tensioner..wont work that way.

[AtvKid4Eva]

ok, well with the tensioner in how do i have enough play to reposition the cam sprocket to line up the markings with the cylinder?

[CJM]

Easy.

Remove the screw cover cap (allen head). Take a small flathead screwdriver and push it into the hole and turn it slightly and it will take the tension off. Mine stayed in there but you may need to hold it.

Line up the sprocket and then put the cam chain on remove screwdriver. It shouldnt move the sprocket. It will line up, it may be sooo super slightly off like a fraction of an inch but its no worry its fine.

If thats all good your overlooking something if its not starting.

You need Fuel, Spark and Timing (which you just verified). So either its not getting enough or to much fuel or your not getting spark.

What is it doing when your trying to turn it over?

[AtvKid4Eva]

It turns over smooth and makes a stumble like it wants to start but won't. I'm gonna make sure the timing is right tonight and adjust the valves since they may be way out of adjustment.

[CJM]

That would be a good start. Make sure its getting fuel, the carb isnt dirty, the sparkplug is indeed firing.

It sounds to me like your carb might be dirty as it wants to start but wont (not getting fuel. Take the boot off the airbox and spray some carb cleaner in it while its trying to start. If it runs you need to clean and or rejet the carb.

[MtnEX]

It the timing is off... just take the tension off and move stuff one tooth from where it seems lined up without tension. Then put the tension back and see what you have.

[AtvKid4Eva]

i set the timing and adjust the valves and it started right up..the only thing is it is make a loud tick from what seems to be the top of the motor and someone told me the decompression on the cam could be sticking? anyone know anything about that? i know the 400ex tick but this is an abnormal tick and it is a stock cam. thank guys

[CJM]

Check the valve clearance again. All 400ex tick tho, depends on oil valve adjustment, cam, etc.

http://www.atvriders.com/articles/valveadjustment400ex.html

[MtnEX]

Originally posted by AtvKid4Eva
i set the timing and adjust the valves and it started right up..the only thing is it is make a loud tick from what seems to be the top of the motor and someone told me the decompression on the cam could be sticking? anyone know anything about that? i know the 400ex tick but this is an abnormal tick and it is a stock cam. thank guys

Sound scary like something is going to come through the side?

If so it is probably just the decompressor.

I think it some cases it just starts to wear out somehow and operate/tap when it shouldn't.

Mine has been doing it for years now.
I think the right thing to do is a cam that deletes it.


How sure are you that the cam chain and tensioner are inside the service limits?

[MtnEX]

This the noise?

<object width="480" height="385"><param name="movie" value="http://www.youtube.com/v/Ep3pi9K-Fn0?fs=1&amp;hl=en_US"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/Ep3pi9K-Fn0?fs=1&amp;hl=en_US" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed></object>

[AtvKid4Eva]

yep it sounds just like the video..is that the decompression sticking?

[MtnEX]

Originally posted by AtvKid4Eva
yep it sounds just like the video..is that the decompression sticking?

Well, I can't tell you for certain because I haven't been in there to inspect....

But I believe the decompressor is just old and malfunctioning from time to time.

It's not too hard to go through the list of possibilities...


Myself, when I first heard it, I thought it was lack of lubrication because it started right after an oil change. Then I thought it was the the wrist pin. Next I thought it might be the cam chain slapping. But then I realized it was probably the decompressor.

Reason being is that if you take a stethoscope or a sounding rod to the engine, it's not down at the wrist pin, and not around the cam chain... In fact, I really can't pinpoint it to save my life... and I think it is because it is the decompressor and is in there with the valvetrain.


I can tell you mine started making this noise over 2 years ago. It doesn't do it all the time. As you saw in the video it's random, and I can sometimes make it stop messing with the throttle. Sometimes I can make it stop by adjusting the idle speed too.


But anyways, the noise has been around over 2 years and nothing has flung through the side of the motor yet :eek2: