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As I write this, the issue is solved but I used this forum and others along with a shop manual to repair my 1998 Honda Foreman 400 TRX400. In all my research I didn’t see many definitive solutions so I figured I’d post this in hopes that someone else would find it helpful in the future if faced with the same problem.

In a nutshell , if you are having a no spark / intermittent spark issue then consider replacing the voltage rectifier / regulator. $27 on Amazon and 5 minutes to replace. It’s not always the CDI / ICM.

Now for the details .. went to crank the bike and it wouldn’t start (had been running fine a few hours before). Would turn over strong but wouldn’t start. Didn’t matter if using the electric start or the pull rope , same outcome. The diagnostics began. Fuel checked out fine , battery checked out fine , all switches on and operational , no blown fuses , no burnt or chewed wires , bike was in neutral , etc. All the easy stuff wasn’t it.

Replaced the spark plug , still won’t crank. Pulled the new spark plug and did a spark test .. grounding it to the block external. 90% of the time , no spark. Every once in a while, especially at the instant the starter button was released it would spark once but intermittently. If the starter button was double or triple tapped versus holding constant , it would spark once. But otherwise no spark.

Found a copy of the shop manual which contains the detailed electrical diagrams for the charging and ignition systems. Also provides the continuity and resistance (ohms) indicators for operational components. First check was the ignition coil , checked out fine. Next was the plug wire and boot , all good. Next was the wiring down to the stator and ignition pulse generator , all good. Individually checked all wiring and grounds in the entire harness , all had continuity where they should and path to ground where they should. Checked for operational switches (mainly the ignition and engine kill switches) , all good. Had the battery load tested at Interstate battery , all good. Getting frustrated at this point ...

Checked the online forums and also called a local dealer and internet parts house. Was led that it was most likely the CDI / Ignition Control Module (ICM). Spent $100 on a new OEM unit but nothing changed. Back to square one staring at the electrical diagram.

Consulted the forums again as well as the dealer and parts house. Next suggestion was replacing the ignition coil. If not that, could be the stator or ignition pulse generator. Basically throw parts at it until it’s fixed! But .. on this forum I found one person who said they had replaced their voltage regulator / rectifier and that solved the problem. I figured it was worth a shot. Looking at the electrical diagram I could see one single wire connecting the voltage regulator / rectifier to the ignition system along the path to the CDI / ICM.

Got the new regulator / rectified in this evening and voila the problem is solved. Sparking strong and it fires right up like it once did. Awesome!

Hope this helps someone!
 

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Good write-up, thanks.
 
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