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Just one bolt

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I spent a long time, on and off, trying to re-jet my carb on my XR400 but I could never get rid of the sputtering and spitting at various, mostly high RPMs.  Then I began to wonder if the rev limiter inside the CDI module was malfunctioning and cutting out the spark intermittently.  I dove into the service manual and started reading about troubleshooting the ignition system.   While I was doing that, I discovered a loose ground wire to the coil.  Tightened down one bolt at the sputtering is completely gone.  Thought I would post in case this might help someone else.

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It's crazy how something so small can cause such a big problem.  I'm working on a project bike right now that has a mystery problem and I'm considering that it's a CDI/ECU issue but I should probably go through all the grounds first.  Maybe I will post up about it later.  

What jetting did you end up going with?  

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Funny how that works out sometimes. At least you caught it (hopefully) before you threw a lot of money at it, which has not always been the case in my experience. 

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17 minutes ago, tntmo said:

It's crazy how something so small can cause such a big problem.  I'm working on a project bike right now that has a mystery problem and I'm considering that it's a CDI/ECU issue but I should probably go through all the grounds first.  Maybe I will post up about it later.  

What jetting did you end up going with?  

I have now set it back to where it was before I added a new exhaust (168 main/45 pilot) and it runs good.  Needle is OC EM R.  Now, I will go through the normal jetting process to fine tune it. (this is a 440 big bore).

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yes on bikes now imagine it on aircraft....it's kicked our butts a few times in the past. don't trust your test meter....remove and burnish/clean reinstall. especially with all these new fangled digital systems.

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In any electrical or electronic circuit, the return path ( ground or Neutral ) is just as important as the hot side. Plus the grounds are much easier to trace. 

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On 8/19/2019 at 9:08 AM, tvscum said:

I have now set it back to where it was before I added a new exhaust (168 main/45 pilot) and it runs good.  Needle is OC EM R.  Now, I will go through the normal jetting process to fine tune it. (this is a 440 big bore).

FYI... down to 158 main/45 pilot

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