Okay, I need some wiring gurus here. The above atv has a weird issue. It will fire right up and idle great. Try to give it throttle and it breaks up like it is hitting a rev limiter. When I turn on the lights it clear right up and will rev out! Crazy, I know. So it must be feeding the cdi 12v some how when the lights are on. I am trying to find a wiring diagram to start staring at it until my eyes cross. Wiring is not my thing. But I have already had some great help with the wiring on a 2017 Recon from @merryman and @papa hogg scoot so I hope we can figure this out. Where would the lights overlap with the cdi? Could it be that the lights are drawing some overcharge from the stator? What I have checked is the battery charge from the rectifier and it maxed out at 14.5 when revving full throttle and is about 12.9-13.5 when idling. So I think the charge system is healthy enough. Ideas?

 

300s have a weird AC/DC hybrid CDI. I have had this problem with overcharging regulators, are you sure it isn't doing it intermittently? I have an old model 420 trade in at the moment, battery flat so started on pull start and checked charging, wanging away at 17.5v. Put a spare battery on, checked again and got a max of 14.5v. Thought all may be well. Then sent it out as a courtesy bike and it came back with a flat battery again. Tested, and again 17.5v, so looks like an intermittent overcharge, battery is now toast too. If it definitely isn't overcharging, it could be the CDI on its way out. I did have a 300 with what seemed like a rev limiter on it. Fitted a new CDI and all was well. Checked the CDI that came off and found it was for the wrong year, genuine ones are colour coded white, green or red wiring plugs depending on year.

 

Like merryman said voltage regulator would be the first thing I would carefully reinspect charging then CDI..The redneck way to check CDI lighty TAP the Cdi with screwdriver handle while CDI is in the rev problem and 90 percent of the time it will clear up while tapping I know this isnt the proper way to test but its the quickest if dont have an good test CDI which I do from over 40 years

 

I will try both ideas today. The intermittent charge is possible because a couple of times it seems to drop to 9.5v but I thought my meter was flaking out.

 

@merryman I ordered a CDI for the 88-94 TRX300FW and it has white plugs and is quite a bit smaller than the one on the ATV that has red plugs. I am a little concerned about installing it. Also I found the light green wire in the CDI harness badly chaffed as if someone skinned it to test?

 

88-93 are enterchangable not 94 the best I can remember

 

The ebay seller listed it for 88-97. I will hook it up and see it it runs.

 

I wanted to give and update so that people who find this in the future can get some ideas. So I hooked up the CDI and no start. So time to do some more diagnosing. Hooked up the original CDI she starts right up and is revving out fine without the lights on. Great! NO! After just 1-2 minutes it starts breaking up with throttle, couple more minutes and it won't rev at all just idle. Turn the lights on and she clears up and starts revving out fine. Ok, let me hook up the meter and see what the battery is doing when I turn on the lights. Start is back up with meter on and no light and she is revving out fine and the battery is reading 14.2...14.3...14.5...14.6 starts breaking up. Turn on lights and voltage drops to 14.3 and she is revving again. Turn off light voltage starts climbing again. This time unplug green wire to regulator and battery drops to 12.7 and she is running and revving great. I'm going to call it: REGULATOR. As soon as it starts it is already at 14 plus idling and in just a few minutes as it gets warm the voltage climbs until at 14.6 the CDI starts flaking out. I repeated this several times to confirm. My other ATV's all run around 13.5 idling and 14.5 revving out. This thing starts at that and kept climbing to 15v the longer it ran without lights on to draw amperage away. I'm going to return the CDI and order a voltage regulator and see what we get.

 

A lot of regulators go just over the 14.5v, though not many 300s, as their alternators are not all that powerful. Fairly sure there were more than three different CDIs. All the non genuine ones have white plugs, 96 on CDI had a wire for the fan, with bullet connector, sticking out of CDI and single plug for the rest of the connections. Earlier CDIs had two plug CDIs, identical looking apart from colours.

 

@merryman the regulator kept climbing as the bike warms up. I did not wait to see what it peaked out because I was in a closed garage working on it. I need to let it run and see how high it goes. The CDI definitely flakes out around 4.6 or higher. So maybe the CDI is bad also? It doesn't take much google-foo to see that these machines were prone to electrical issues over the years. A brand new Honda regulator for partzilla is $257! That is why we are all stuck buying chinese junk parts for these things. Maybe I will put a regulator and a CDI on and see what I get. I did see a factory used regulator on fleabay for $20. Maybe I will risk a used one.