XR400 Cam in 400EX

[Dub]

I just picked up a used XR400 cam and plan to instal it in my EX along with a 10.8 JE piston and a 39mm FCR carb. I already read all the info about setting the squish to .040 and plan to do that when I put it back together. I am running an open airbox and a Pro meg E series exhaust. My question is should I take the decompressor off of the cam or leave it on? I have read that they will cause a tapping noise sometime and dont want to have to go back in the motor again. I have an XR600 that taps in the top end and I believe that this is the cause. So I want to prevent it if I can. Or can someone tell me how to install the cam correctly with the decompressor so that it wont give trouble. Does the above combo sound like a good all around trails and woods choice? Thanks, Dub.

[Cannonball08]

you should leave the decompression assy. on the cam and make sure you leave the little spring in the head.

[drthrottle]

cannonball is prolly right. When i rebuilt my ex to a 440 I installed the xr cam w/compression setup. It did make some noise too. Do be carefull to not loose or drop the spring in the head, off in the motor. I tried 2 different springs before it got quieter. But you could hear it at idle.

[Dub]

Thanks for the input. Does anybody else have an opinion on the combination? I want to make more bottom to mid range torque. Am I going in the right direction? Any suggestions would be helpful. Thanks, Dub.

[drthrottle]

Now that you didn't say. I can tell you the HRC does NOT do that. I have one with and one without, the one without has the torque. It's pretty apparent between the two.

[sickmojave]

The HRC cam and XR cam are not the same. I run the XR cam and it makes good bottom and mid range power.;)

[drthrottle]

That's what I'm saying. The xr had the stuff. The HRC will beat you in a drag race and definately on a mx track. But, for fun and trails not HRC.

[Dub]

Thanks guys. That is what I was looking for. Someone who was actually running the XR cam and new how it performed. Now I just have to get busy and get everything instaled. What are you running along with the XR cam? Carrying my big behind it needs all the torque it can get. All it wants to do now is pick up the front end exiting a turn. I want it to slide the back end around enough that it is a controlable slide. The Holeshot XCTs dont help the problem either. Thanks again, Dub.

With the XR cam you will loose some bottom end over the stock cam. Not as much as you would loose with a HRC cam but it is still a long duration cam which will add top end and hurt the bottom end. But with the little bit high compresion piston it should still run good and may not even notice the loss of torque due to the increase in power!