Another KZ400 Cam Timing Thread

When I first put this engine together, the arrow was pointing slightly down or significantly up.
I settled for slightly down since this seemed to be the closest to what the manual asked for.
Everything seemed good. I've done a number of heat cycles and the rings settled right in. It idled nicely and had crisp throttle response. I haven't actually taken it out and put it under load because it has brake issues I want to tend to.
Well I just got around trying to sync the carbs and my vacuum was 7 in. Yikes.
I did a compression test and it checked 100/100 left/right. From what I've read here, it should be significantly higher.
In my mind, this all points to the cam not being set correctly. I just changed the cam to the advanced position. Here's a picture:



I'm inclined to put it together and try it like this but I'd really like to get the opinion of the forum since you know more about this engine than I do.

What is the valve lash set at?


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My manual calls for .10~.15mm. I'm sure I would have went for the .13mm nominal. I'll re-check it when it goes back together.

I re-read this thread: www.kzrider.com/forum/2-engine/610670-kz...or-solution?start=24 and I now think I had it correct with the arrow pointing a bit down. Loudhvx points out that chain stretch will cause the arrow to be off. I would guess on my motor it's low by around 1/3~1/2 tooth which seems to be in line with what he's saying.

But now I'm puzzled how this much retard on the cam could cause such a drastic drop in vacuum?

When I get time, I think I'm going to slot the holes in the cam sprocket so the arrow is at least level if not a bit high.

When you checked compression, was the engine at operating temperature and the throttle held wide open?

Yes and no. Forgot to crack the throttle. I'll recheck it once it's back together but I've never seen a huge difference other than it reaches it's max value sooner. Certainly worth checking though.

I find the lack of vacuum most curious. That's what led me to think the valve timing might be off in the first place.

Easy wrote: My manual calls for .10~.15mm. I'm sure I would have went for the .13mm nominal. I'll re-check it when it goes back together.

I re-read this thread: www.kzrider.com/forum/2-engine/610670-kz...or-solution?start=24 and I now think I had it correct with the arrow pointing a bit down. Loudhvx points out that chain stretch will cause the arrow to be off. I would guess on my motor it's low by around 1/3~1/2 tooth which seems to be in line with what he's saying.

But now I'm puzzled how this much retard on the cam could cause such a drastic drop in vacuum?

When I get time, I think I'm going to slot the holes in the cam sprocket so the arrow is at least level if not a bit high.

If you are going to slot the cam sprockets you should take the time to time the cams properly with a degree wheel rather then just lining up the arrows. Its also possible your rings have not bedded in completely allowing for some leakage. do you have a leak-down tester?

I wish I had a leak down tester. I think the rings have bedded but the valves might be able to cause my symptoms and I just lapped them.
Once I get the cam dialed in to it's proper location I'll at least have eliminated that.
If the issue is still there, I think I may know where I can borrow a tester.
I think what puzzles me more than anything is how well it runs with so little indicated vacuum.

Well, that was an exercise in futility. I clocked the cam 4.84 degrees and any changes were negligible.
The intake vacuum is still low and the compression increased 5 pounds. It's now 105/105 with the throttle closed and 112/112 with it open.
At least I learned that the cam chain must be close to the end of it's service life and this engine is not very sensitive to a retarded cam.

4.84 ?
If you are moving your cam timing around { i.e. degreeing }
Set the intake centerline between 100 and 110 degrees.
This will bring up cranking compression since it would be advancing the cam vs. the 113 degrees which is stock from the factory.


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