cam issue on 400ex

[sloppyjoe]

is it possible to run a stock cam without the little decomp. pin in the head? i took it out when i was running my hot cam, and it stipped the splines off so i had to put the stock cam back in. i cant get it to run, but i dont have my little decomp. pin anymore and was wondering if it would work.

[JOEX]

I guess not, someone else here is having the same problem:(

[400exrider707]

Im having the same problem right now, I think you either need to have the spring and plunger in, or you can take the mechanism off of the stock cam somehow!? Does anyone know how to do that? Does it need to be pressed off? I need to have this running by friday! Or does anyone have the spring and plunger laying around that they want to sell! I will pay for overnight shipping!

[DAVE14]

Im not sure I want to get rid of mine but its something you can make very easily that spring isnt very stiff or anything special & the pin is nothing but a roll pin if youre interested Ill measure exact lengths & diameters of the spring & pin & like I said that isnt a very strong spring so just about any spring in that hole that will push the pin out the same length should be fine. any way let me know I cant see how it wouldnt run without it but it wouldnt be hard to duplicate these parts.

[400exrider707]

Originally posted by DAVE14
Im not sure I want to get rid of mine but its something you can make very easily that spring isnt very stiff or anything special & the pin is nothing but a roll pin if youre interested Ill measure exact lengths & diameters of the spring & pin & like I said that isnt a very strong spring so just about any spring in that hole that will push the pin out the same length should be fine. any way let me know I cant see how it wouldnt run without it but it wouldnt be hard to duplicate these parts.

Well I thought the same thing why wouldn't it run without these parts? I've yet to get a straight answer from ANYONE! I've come to my own conclusion with the help of bradnea that the mechanism on the stock cam is keeping the exhaust valve open and the spring and plunger are what deactivates it. You think you could post some pictures of those parts up? That would be most helpful. Thanks.

[velocityatv]

All the decomp devise does is make sure that the engine doesn't sit with comp in it. It also protects the starter from trying to start the engine while fully compressed. I don't see why it wouldn't start without this. Or even with it partially dissasembled

[velocityatv]

acctually I revise my previous statement : After further thinking I remember that when you purchase an aftermarket cam I believe they incorperate the decomp into thier grind on the exhaust lobe of the cam.

[Colby@C&DRacing]

the intended purpose of the decompressioner on the 400ex is to lessen low rpm compression which allows the starter to turn the motor over easier.

"they incorperate the decomp into thier grind on the exhaust lobe of the cam."

if this was the case the motor would have low compression all the time.


with the stock cam you will need to use the spring and plunger. You could take the decompression device off the stock cam and run with out it and the spring and plunger

[400exrider707]

Originally posted by Colby@C&DRacing
the intended purpose of the decompressioner on the 400ex is to lessen low rpm compression which allows the starter to turn the motor over easier.

"they incorperate the decomp into thier grind on the exhaust lobe of the cam."

if this was the case the motor would have low compression all the time.


with the stock cam you will need to use the spring and plunger. You could take the decompression device off the stock cam and run with out it and the spring and plunger

Ok thats what I've been looking for. So will it be a pita to start without it though? I have someone coming to look at buying it this weekend and I dont want to sell him something thats going to give him problems.

[Colby@C&DRacing]

not on a 400ex :)

[bradrenea]

Originally posted by 400exrider707
Im having the same problem right now, I think you either need to have the spring and plunger in, or you can take the mechanism off of the stock cam somehow!? Does anyone know how to do that? Does it need to be pressed off? I need to have this running by friday! Or does anyone have the spring and plunger laying around that they want to sell! I will pay for overnight shipping!

I have never had to have it done, but I have heard that the flange that the gear bolts to must be pressed off to get the decompression ring off.

[400exrider707]

Originally posted by bradrenea
I have never had to have it done, but I have heard that the flange that the gear bolts to must be pressed off to get the decompression ring off.

This sux big time!

[sloppyjoe]

ok i'm back, i hope with some helpful info. i put a hot cam stage one in my bike and it fired right up. so i have came to the conclusion that it has to have the whole assembly stock to run the stock cam. the stock setup actually opens the right exuast valve to releive the comp. when i had that valve adjusted way out it would run, but as soon as i adjusted it to speck it sounded like it was out of time. i hope this helps some out there! finally got mine running after a few headachs, but thats part of it. :cool:

[K_Fulk]

Originally posted by 400exrider707
This sux big time!

Its only about a 5 minute job if you know anyone that owns a press.

[motoman00440es]

Or you can take a cut off wheel and cut the lobe that opens the valve when starting off I did it to one of mine and it worked fine

[400exrider707]

Originally posted by motoman00440es
Or you can take a cut off wheel and cut the lobe that opens the valve when starting off I did it to one of mine and it worked fine

That sounds pretty cobby, but if it comes down to it I might just do that, lol.

[400exrider707]

Ok heres the deal I put the plunger and spring back in and voila! Started right up. So for future reference if you dont have the decompression plunger and spring in, using the stock cam with the decompression mechanism in place, it wont start!