UPDATE: Hot Cams auto decomp exhaust cam in YZ400

Took my first ride with the Hot Cams auto decompression exhaust cam installed in my all stock '99 YZ400. Starting the bike was amazingly easy..it started the first kick with my flip-flops on. Once started, I noticed that the valves were noiser. The profile of the HC cam is taller and more narrow than the stock cam, so the valve must be hitting into the valve seat harder, therefore making more noise. It's not distracting loud, just a bit louder than stock. It sounds like loose valves, but everything is well within spec.

From what I understand, only installing the exhaust cam shouldn't change the performance of the bike, but I noticed some differences. I tested the bike on my enduro circuit which includes fire roads, singletrack, and double track. The first thing is the bike felt like it had less power. The midrange hit seemed to be less present, and was slightly higher up in the rpm range. Now, let me expand on my "less power" statement....at first the bike really did feel less powerful, but as I would come into each corner, I noticed I was going much faster than usual. After settling in a bit, it became clear that the bike wasn't slower, but the power was more dispersed if that makes sense. I'm not sure if it has more low end power, but the power is just spread out much better. It's pretty deceptive on how fast I was going since I felt slower....kinda hard to describe.

At this point in the test, I turned the bike off to see how it would start after running for an hour in 100 degree heat. It started on the first kick with no hot start. Excellent.

Now, on to stalling. On my circuit, there are many tight, switchback, downhill corners. Before the mod, I would come into those with mostly the front brake on, feathering the back brake since the bike would stall if the back brake was applied to hard, then after stalling the rear wheel would lock up and it was a trick to bump start it through the exit of the corner apex. After the mod, and much to my delight, I held my speed up right before the corner, then I jammed on the back brake to create a controlled rear wheel slide just like a 2-stroke and guess what...the bike didn't stall...it just idles through with the rear wheel locked up. I can tell it wants to stall, but the auto decompressor must be just letting it click over since the rpm's are low enough. Further, I did stall the bike on some really steep downhill singletrack and it was like it never happened since it bump started so easily. No more locked wheel downhill rodeo rides after stalling the bike! Amazing.

So far so good!


You are right on of your assesment. The power is now in a different place that's all. I remember after I installed my HC cam, the first 15-20 minutes I thought "that was a waste of $200!) After a while though I noticed my transitions were smoother and like you said, I was carrying more speed into the corners. Now I love it. If you miss the low end punch you were getting, and if you do not have the PowerNow, give it a try. I think you'll like it. Have fun, be safe.

I had Hot Cams intake and exhaust cams on my 426...it didnt make less power...just moved more it to the mid and top range of the power. I hated it at first but it made the motor alot like a REALLY fast 2 stroke and eventually learned to love it.

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