Hi All, I have been repairing ATV's for many years. Have not done many Hondas.
I have here yet another TRX300A with a NO Spark / Intermittent Spark Issue. I say yet another because after reading the posts here as well as other sites over the past 3 days it seems there is a lot of these. Here is the other thing I noticed. Anyone that has the problem I am about to describe seems to never update the posts with the solution unless it was something simple like a new CDI or other easily swappable part. But the people that have replaced every part and are still having the exact same problem as I am experiencing never seem to come up with an answer to fixing the problem.
So, Here we go.
1994 Honda TRX300A Fourtrax 2WD
ATV is in great physical condition and sat for the last 6 years from a no start issue. No one had worked on it and all the parts were original. I determined right away it had no spark. I went through the entire ATV checking everything. Bought a brand new battery. First I checked all the wires to the CDI Box because I know this seems to be the biggest issue with these. All wiring was good, I especially checked the grounds. A friend has the same model year TRX300A, so I took the CDI and tried it in his ATV. NO Spark.. I ordered a new CDI for this particular model. I also hooked up his CDI into my TRX300 and got no spark. Put it back in his and it works great. Tried the new CDI Box in his and it worked fine. I put in the new CDI and still no spark.. I tested the ignition coil and it was fine. Have a new coil also for testing. Spark Plug Fine, Had a new plug to also test with. Tested the Pick Up coil. Readings were outside the spec so I purchased a new pick up coil. Tested the new one before installing and it was dead on with the spec. I not only used Hondas method of testing in the service manual I also used the specs from rmstator.com , they are a great source of information and specs for individual models. They give you the specs and testing results you should expect. I was having some inconsistent readings from the stator so I got a new one. Just to add, I do have a DVA Adapter. I installed the new Stator and Pick up coil. Once installed they tested to spec. I had been testing the spark the usual way. Remove spark plug , hold it against the head and crank it over. As I had read so many times in different forums, people were getting a brief bright spark from the plug when turning the key on and while cranking the engine you got the same bright spark while switching the Run / KilI switch off and on, but no spark while normally cranking the engine. I was now getting that Bright spark under those same conditions. It seemed the new stator, pick up coil and CDI box were now letting me see a spark. put the old CDI in and no spark at all. So the CDI was bad. I then tested the Neutral reverse switch at the plug and it tested fine. The Neutral and reverse light are also functioning properly. While cranking over the engine checking the Stator showed within spec. Since these have a wire running from the Rectifier to the CDI I got a new Rectifier for testing. Still same spark results. I then went through all the wiring, checking and cleaning all ground contacts. I tested all Handlebar switches and ignition switch for continuity and function. Everything checked out. Checked all fuses and connections. The only suspect connection I found was on the starter switch plug. I completely cleaned it with contact cleaner and it was shining like new. Put in some Dielectric grease and it was good as new. So the only two parts left are the Magnetic Flywheel which has strong magnetism observed while putting in the stator and small encased diode that goes to the neutral light. I have a new diode coming even though this one seems to be testing okay. I guess you could consider the alarm box, but from everything I read it cannot interfere with the spark. Am I wrong?

Does anyone know of someone on this forum that replaced all the parts, still had no spark and was able to figure this problem out?

Thanks for any help, I am stumped as of this moment.

 

Have you tried kick starting it, with the new CDI fitted? Your problem sounds a lot like the "won't spark until you take your finger off the start button" issue. Most owners learn to live with it as, if you keep pressing button on and off, one spark will "catch" and the engine will run. I did cure the fault on a 350 (same CDI as late 300s) It turned out to be the neutral wire. This increases the spark in neutral so, if faulty, doesn't give a powerful enough spark for engine to start when power is also being used by the starter motor. Trouble is, Honda kept changing how that pale green wire worked on the 300, and changing CDIs to suit. Fit the wrong CDI and it will be getting the wrong signal from that green wire.

 

Hi, Thanks for the reply. When kick starting I get no spark at all. The spark it gets when turning on the ignition I believe is just from the battery power as the engine is not even turning over, something must be letting that voltage feed through initially. I can't say I have looked to see if I have a spark once I let go of the starter button. I will check today and let you know.

 

Hondas are a strange mix of DC and AC CDI. Can't remember if a stator yellow wire is fed to the CDI on 300s, one is on the 450s, which uses one of the 300's CDIs but power for the spark comes from the battery. 450s won't run if the regulator fails, but you have fitted a new reg so it can't be that. If there is no spark when cranked by foot, it seems like you are not getting the pulse signal from the trigger coil. Have you checked the pulse AC voltage at the CDI plug when engine is spun over? As I wrote above, the wrong CDI for the year can cause problems too. They have colour coded plugs and sockets, but non genuine CDIs all come with white sockets, so it is bad to tell if you have the right one, someone on here recently was sold the wrong CDI by a supplier who didn't know the difference.

 

Honda ATV 1994 OEM Parts Diagram for Wire Harness | Partzilla.com

 

I have had several of these photo 12 go bad its a diode

 

Yes, a stator wire does go to the CDI box on this one. I had tested the pulse coil, before I installed it, after I installed it ( Ohm reading was perfect ) Then I tested it while cranking and the voltage was in spec. After I read your post today, I figured I would do all the tests again and write down the results to post here. I decided to do the voltage test while cranking first. The voltage showed up and a second later disappeared then I tried it again and it was there. Tried it a third time and it was gone. I took off the crank case cover of the stator. I did a continuity test on the Pulse coil lead to the three pin plug at the end of the harness. I kept moving that wire for a while and I finally found it. There is the slightest break in the wire right at the Pulse coil connector. The break is inside the wire jacket. I cut the wire back and soldered the connector on. Hooked it up put the cover back on, filled it with oil and it cranked and started. That was the issue. Then I went back and reinstalled each old part I had replaced. The CDI was Definitely bad. Original Pulse Coil was bad and original stator was bad. Original Rectifier was good. Original coil was good. Original Spark Plug was good. All other related parts were good. Now I need to rebuild the carb and get it running its best. Once I am done I will mark this thread solved. Thanks for your post. It made me run all the tests again.