possible decompresser problem

[jaredbeast]

Just got my first 400ex the other day and it has a pretty loud ticking coming from the top end, more specifically the right side. I read the repair manual and talked to some people and everything leads to the decompresser. I tried to break it free with a breaker bar on the crank but that did not work. My question is, what is the best way to go about fixing this problem? should I go to the dealer and get a new decompresser assembly or just buy an aftermarket cam (stage 1 hotcam). I am not worried about performance and much as reliability. I have also heard these quads don't take well to mods. If someone could shed some light on my situation it would be very much appreciated.

[CarGuy7a]

the only reason a 400EX (or anyother quad) will not run well with mods is if they are not done correctly just like any kind of engine in any vehicle wheter it's a car you drive on the road or an atv.

when you say ticking from the right side are you talking right side of engine as if you are sitting on it or looking from the front?

also how does it run? if it runs fine and you just have the ticking the valves need adjusting.

if it runs completely wierd and you hear odd noises coming from the top end then it could possibly be the decompressor. (Actualy i'm not sure if it would even run if the decompressor is hanging up.)

the decompressor is located on the shifter side of the engine.

[kuba1506]

i just had the same or sorta the same problem. i bought my 400 in october and had a horrible ticking on the right side. so i thought i would go get my valves adjusted. i got them adjusted to specs and the bike would not run at all. it ran even worse after i got the valves adjusted so i told them to just find the problem and get it fixed. MY problem im not exactly sure about your situation but it does have most of the symptoms that mine had.

The problem was that my decompression pin was actually broke. when the cam roles over it pushes on that pin letting exhaust gases out (Correct me if im wrong on that) and that pin was not gettin depressed when the cam would role around to hit it causing the valve to stick open and run crappy.

what i did to fix my problem was the dealer i took it to put the new decompression pin in and roled the motor over to see if the valve was still sticking which it was. so they put in a brand new cam as well.

[CarGuy7a]

i just wonder if you could actually take the decompressor off of a stock cam and put the cam back in.

i've got a stage 1 hotcam in mine and it said not to use the decompressor with that cam.

[jaredbeast]

Originally posted by CarGuy7a
the only reason a 400EX (or anyother quad) will not run well with mods is if they are not done correctly just like any kind of engine in any vehicle wheter it's a car you drive on the road or an atv.

when you say ticking from the right side are you talking right side of engine as if you are sitting on it or looking from the front?

also how does it run? if it runs fine and you just have the ticking the valves need adjusting.

if it runs completely wierd and you hear odd noises coming from the top end then it could possibly be the decompressor. (Actualy i'm not sure if it would even run if the decompressor is hanging up.)

the decompressor is located on the shifter side of the engine.

The clymers manual says that the decompresser holds the right exhaust valve open and thats where the sound comes from if the decompresser is malfunctioning. The decompresser itself may be on the left side (shifter side), i'm not sure since I havn't looked into it that far yet.

Does anyone know if I can put a new cam in without removing the top end?

Does anyone know if its safe to just put a stage 1 cam in with no other mods?

edit: the quad is actually running very strong and the valves are all in perfect adjustment.

[GPracer2500]

The auto-decomp/anti-kickback mechanism is not on the shifter side. It's on the right side--the same side as the exhaust valve that gets held open a smidge when the mechanism is active (rpm < ~800rpm). It's right next to the cam gear flange.

The mechanism can be removed from the stock cam. It's pressed on/off of the cam along with the cam gear flange. The gear flange is actually what holds the mechanism in place.

It should be fine to remove the mechanism. The EX's starting system is robust and even modded high compression EX engines seem to have no trouble turning over with no decomp mechanism. A HC1 camshaft is also a fine idea if you want to get rid of the mechansim. Cams can be removed and installed pretty easily. Only the valve cover (and related items) need to be removed to gain access. The head itself can remain in place.

You might also look into the noise coming from the cam chain tensioner. It's also on that side of the engine. A mechanics stethiscope may or may not help you isolate the source of the noise.


Sidenote: the anit-kickback part of the decomp mechanism is mostly unnecessary on the electric starting EX. It's a vestigal component left over from when the EX's engine was kickstart only in the XR400R.

[CarGuy7a]

[QUOTE]Originally posted by GPracer2500
[B]The auto-decomp/anti-kickback mechanism is not on the shifter side. It's on the right side--the same side as the exhaust valve that gets held open a smidge when the mechanism is active (rpm < ~800rpm). It's right next to the cam gear flange.


yeah sorry about that. it's been a while since i've been in there. i need to bring my clymer in the house to look at it.

but yeah my motor is pretty much stock except for the stage 1 cam and it runs fine.

it's a good investment if you want to spend the $$$.
but if you don't want to spend the $$$ right now i would just take the decomp. mechanism off and put the stock cam back in.