tvscum 43 Posted August 19, 2019 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. 1 Share this post Link to post Share on other sites
tntmo 882 Posted August 19, 2019 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? Share this post Link to post Share on other sites
TexasDualler 32 Posted August 19, 2019 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. Share this post Link to post Share on other sites
tvscum 43 Posted August 19, 2019 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). Share this post Link to post Share on other sites
robertaccio 405 Posted August 19, 2019 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. Share this post Link to post Share on other sites
Bagstr 287 Posted August 19, 2019 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. 💡 Share this post Link to post Share on other sites
tvscum 43 Posted September 4, 2019 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 1 Share this post Link to post Share on other sites