I am trying to fix up my grandfathers 88' fourtrax 300. The only reason he quit using it was because he got a new one years ago. But it sat around for a few years and never got used. So we tried starting it 2 years ago, and it would not start, it wasnt getting fuel. I could put a little fuel in the cylinder and it would run for a few seconds, then die. So it sat for the past two years outside in the weeds, previously it had been stored in the barn all its life. So just recently I took the carb apart and rebuilt it, and I found out why it wasnt getting fuel 2 years ago, I have never seen a carb that dirty!! I can tell you for a fact that carb hadnt been touched since 1988! So I got the carb all done, new fuel in the tank, and when I went to start it I now have no spark. So I bought a new coil and put on it this morning, but still no spark at the spark plug, plug is also new. Any ideas? It sat for two years in the weeds and lost spark??? It doesn't appear that any wires are chewed by mice or anything. Thanks!
no spark on my 88 fourtrax 300
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Welcome to the forums. Make sure you have the kill switch in the "run" position. Check over all your wiring good. If you don't find any problems, I'm going to guess and say that your CDI is bad. A bad CDI is a pretty common problem on the Fourtrax 300.
I know the bike is in the run position, but I will tear in to that and see if the contacts are corroded, since it was sitting outside when something occured that caused me to lose spark. How do I check voltage at the coil? It seems like I have checked that with a multimeter, but got no results. I am assuming I should have 12v? Will 12v always be there, or only when I have the starter engaged? Or should there be 12v to the coil the instant I turn the key switch on? Hopefully it is something simple, caused by a bug, rodent, or even moisture from sitting out in the weather for 2 years. Does the CDI box go bad just setting over time??
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Yes, they can. I've never had a CDI go bad while the ATV was running, it's always after it's been off and when you try to start it back up. I'm not saying that they can't go bad while the ATV is running, but I've never had one do that. I've heard of it happening a few times, though.
ok so I took apart the run/kill swich off the handle bar, and I dont see how to get a visual on the contacts. I cant even managae to get the kill switch button off. Also how can I measure for voltage at the coil? can I have voltage at the coil even if the cdi is broke?
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im not sure that if the cdi is bad that you will get voltage at the coil or not, but you can use a test light to check at the coil. try checking the connection where the wire harness connects to the cdi, the contacts in the plug in can corrode and you won't get spark.
ok, I got the front fenders off and have access to the cdi. There is actually two "electronic boxes" up there under the front fender. I dont know which is which, but I uncoupled both of them, all the connections, and everything looks good and clean. No signs of corrosion anywhere, just a little dust on the "electronic boxes". Can I check voltage on the wiring harness at the connection point, if so, how?
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One box is the CDI and the other is the alarm unit. The biggest box should be the CDI.
There isn't a test for a CDI, other than replacing with a known good one. But you can test the wiring going to the CDI at the plug on the wiring harness side, but you have to have a peak voltage tester, a regular voltmeter or multimeter won't work. You will need a service manual for the specs. I have a service manual for the 1995-2000 Fourtrax 300, but the specs might be different than for the '88 model.
I have the clymer manual for this fourtrax, and I have a peak voltmeter also.....somewhere. By peak, I assume you mean one that keeps track of the highest reading? I still dont know how a CDI can go bad just sitting there. If I do require a new CDI, is it a good idea to get a "high performance" cdi? I have seen some on ebay that sound like they are better that oem.
well I just ruled out the possibility of my problem being the kill switch. Everything looks good and shiny there and a continuity test tells me that electrons can flow freely through that switch. Also checked both fuses back by the battery area, all is good, except for the 500 tiny ants I found living in one of the fuse holders......nothing a shot of carb cleaner wont kill!
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Yes, because it won't have a steady voltage, it will be a pulse.
I don't know, I've always used stock/OEM, but I don't see what it could hurt.
Also, it's possible that it could be the pulse generator. Your manual should tell you how to check that. You should be able to check the resistance at the connector plug with an ohmmeter.
I just tested the pulse generator, at the connection point, of course. As stated in the manual, my reading was 347 ohms, which is acceptable between 290-360ohms. I have tested the coil, I have tested the kill switch, the batter is brand new, both fuses are good, and I have 12v at the line side of the CDI box. I am not for sure what the alarm box does or if it is part of this mess, but would I be right to assume at this point that I need a new cdi? Any idea why it went bad sitting out for 2 years?
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The alarm unit is part of the oil temp system, it receives input from the oil temp sensor and operates the oil temp light.
If I were in your situation, I would try a new CDI, since you've pretty much ruled everything else out and a bad CDI is a pretty common problem on the Fourtrax 300 when they quit firing. I can't guarantee that's the problem, but that's what I think it is. I don't know how or why the CDI can go bad just sitting, but I've seen that happen, so I know it can.
speaking of the oil temp unit, it seems to me as a kid that when we would start the four wheeler the oil temp light would come on when the key was turned to the on position. Now when I turn the key on, the only thing that comes on is the neutral light. Does this have anything to do with the problems I am having. Maybe the CDI box and the alarm unit box are both bad? Also, should I have any voltage to the coil, if the CDI is bad? I have tried testing for 12v at the coil and I get zero, but of course the coil is on the load side of the CDI, so if the CDI is bad, maybe the 12v cant get past the cdi to the coil? My neighbor has a big red three wheeler, could I use his CDI to test and see if it will work on my fourtrax 300?
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Yeah, the oil temp light should come on for a few seconds and then go back off, when you turn the key on. I don't think that will keep it from firing, but I could be wrong. I know when the oil temp light comes on, they will still run. The service manual should tell you how to test the alarm system.
I doubt it, because the CDI fires the coil. Also, it wouldn't be a steady voltage, it would be a pulse.
I doubt if it would be the same, but I can't say for sure, because I've never tried it.
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i don't think that if the oil temp unit is bad it will keep it from firing. i just worked on an 88 model 300 that sometimes the light would work and other times it wouldn't, and it ran fine. as for going with a performance cdi, if it were a sport quad i would put a performance cdi in it, but since its a utility bike the stock cdi would be fine. the big red cdi probably won't work because it uses a different wire harness but if the plug in on it is the same as the 300 its worth a shot.
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38,589 Posts
have you checked your pulse generator ?..checked the stator ?..and also there is a diode that's in the wiring warness ..this also will keep this atv from firing. try kick starting it..watch your nuetral light..does it glow when you kick it over ?..if so..then your charging side of your stator is working at least...there is two sides to a stator..one fires the c.d.i..the other charges the battery...if your stator is good..your pulse generator is good..and your diode is good. and your kill switches are ok..then this means your c.d.i is bad...before you go buying a new c.d.i..check all your ground wiring..also unscrew the spark plug cap off the coil wire..try cranking it over while you hold the spark plug wire alittle ways from the engine cylinder...if you get spark then..means your spark plug boot isn't letting spark through the wire..strip the coil wire back some..screw the the boot back on the new coil wire..then see what you get...as for testing the diode..use a paper clip..jump the conections with it.then crank it over..see if it fires..if it does..then your diode is bad...DO NOT RUN THE ATV WITH THE PAPER CLIP IN IT !!
SUCCESS, maybe? Well, I tried testing the diode thing, and I couldnt get an ohm reading between the two terminals. So, I just pulled it out, bypassed it with a paperclip, and wallah the darn thing runs! So I put the diode back in, and to my amusement, it still runs! So I start it and then pull the diode out while it is running, and it still runs! The only thing that changed when I pulled the diode out while it was running was, the neutral light went off; when I plugged it back in, the neutral light came on. Oh, also my oil temp light is now working properly also. When I turn the key on, it comes on for a few seconds and then goes off. Before I monkeyed with the diode, the oil light never worked either. So really I have no idea what I did to make this thing start getting spark, I must have wiggled something. So then I started it and while it was running I started wiggling connections, but I could not get it to die or lose spark. Any ideas are appreciated. Thanks for the help so far........I am sure glad I didnt go and buy a new CDI box, which was what I was going to do by the end of the night. Again, thanks to all who posted in an effort to help me, and an effort to keep these bulletproof machines on the trail.
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your welcome !..that diode controls the nuetral light in the wiring harness..if the c.d.i doesn't know your in nuetral..it won't fire at the plug..soooooo..when you checked it like i said..it probally was not making good conection..glad you found your problem !
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