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Troubleshooting Flatspot

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So I bought a DRZ400 recently and it was 'perfect' when I got it. A few weeks later the Cam chain tensioner failed (a common problem with the earlier models I've heard). It started having a loud clicking noise but still rode perfectly fine so I did ride it a few times whilst waiting for my manual cam chain tensioner. (offroad was too much fun)

 

A few days before my new tensioner arrives it dies and refuses to start but would turn over, kind of like a battery problem but would sometimes not work even if hooked to a car battery.

I install a new cam chain tensioner and a new spark plug in the process and now she runs great, no cam chain noise, turns on without hesitation. Only problem is now I get a flat spot around 5000 rpm and a 'redline' around 7500-8000 (the redline is meant to be 11000 afaik?). Also, I had to adjust the idle screw so that it would idle, it used to idle fine how it used to be set. (Could something have changed in the carby?)

 

I checked the timing when I was doing the cam chain tensioner so that is fine although I plan to re check it.
The problem only seems to be obvious at a half throttle position, having it Open the bike will climb through the revs well enough. Also whilst the bike is cold it seems to work fine and then it begins to flatspot once warm.

So far from other forums the suggestions have been
-CDI
-Carby needing a clean/ adjustment
-Valves damaged

 

 

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In hindsight wasn't my best decision.
There are numerous videos with the clicking nosie that made it out to me like it was pretty normal on a DRZ to have a clicking noise of some sort.

Timing was still find when I got the valve cover off and realise just how screwed the Cam Chain tensioner was.

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What carb? What jetting?..what engine mods?

 

What are you using as a tachometer? Is it accurate?

 

Rev limiter is @10,000 rpm....power is starting to drop quickly @8,000 rpm on a near stock drz engine

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Fully stock AFAIK. Just bought it.
Has an aftermarket Tacho so it might not be 100%, but the 'redline' doesn't seem to be consistent. More worried about the flat spot at 5.5k.
Valve Clearances are within spec.

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Fully stock AFAIK. Just bought it.

 

 

If a jet kit is not installed , this is where I would start......stock drz400 are notorious for being lean from the factory...

 

 

JD Jetting Jet Kit S/SM  +ThumperTalk Fuel Mixture Screw is what I would install...

 

 

And do the 3x3 mod....http://www.youtube.com/watch?v=VtKWbs0N5lo

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Noticed that screw is for the S or SM model.
Doesn't that run a different carb to the earlier E models??

Thread the same on both?

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