98 yz400f.. problems cranking

14 replies to this topic
  • yz400f

Posted July 04, 2004 - 11:30 AM


Sup guys,
im having difficulty cranking my 98 yz400f. it had been cranking fine, usually within 2 kicks or so. i had ridden it about a week or two ago and just sprayed it down afterward with the hose. the only other thing that i have done is i had taken the exhaust header pipe and silencer off, cleaned it, and reinstalled it. i didnt remove anything else. i changed the spark plug today. im sure the valves are not sticking open because it still has compression. i tried spraying a little starter fluid under the seat and that did not help at all. any sugggestions welcome! thanks

  • yz400f

Posted July 04, 2004 - 12:28 PM


well i re-took the header pipe off and made sure it was seated correctly and it is. i continued to try to kick it off but it never fired up. so i took the spark plug back out. there is no blackness at all on the spark plug, but htere was some gas on it, leading me to believe that the bike is not sparking. what all controls the ignition on the bike? i need to find a way to test the coil, and if its not the coil find out what else it could be :thumbsup:

  • rush66

Posted July 04, 2004 - 01:04 PM


take the spark plug out and put it in the lead and touch the spark plug to the head kick it over while watching the plug you should see it spark if not somthing in the electrical system is wrong

  • yz400f

Posted July 04, 2004 - 01:21 PM


i dont see a spark.. what should be the next thing to check?

  • sirthumpalot

Posted July 04, 2004 - 02:24 PM


Try a new spark plug before you go further.

  • yz400f

Posted July 04, 2004 - 04:52 PM


already have, tried the one that was in it and 2 other brand new ones

  • Hamish

Posted July 04, 2004 - 10:17 PM


unscrew the HT lead from the plug cap. Place the bare wire end close to the engine case and kick it over looking for a spark. The 'fun' way to do it is to get an unsuspecting frind to hold the lead whilst you kick it over :thumbsup:
If that fails check the voltage on the primary of the coil (it will be AC). Never try and measure the voltage on the HT lead as it will smoke your multimeter every time. Easist way to do this is to remove the plug (or hold in the decomp lever) and push the bike with it in top gear. If you have no voltage there check the kill switch wiring. If thats ok you have a dead CDI or stator. Hope this helps.

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  • YZFan

Posted July 05, 2004 - 01:05 AM


Before you get to deep in diag. check to see if the kill switch is bad unplug it under the tank and try to start it. I had the spring in the kill switch break before and it caused the same problem. Good luck.

  • yz400f

Posted July 05, 2004 - 05:36 AM


alright, i checked out my kill switch with my multimeter and the switch is working properly. my question now is, the wire i should be testing for AC voltage on, is it the little wire on the bottom of the coil? its not the ground or the wire going to the spark plug.

  • yz400f

Posted July 05, 2004 - 09:22 AM


well i got out my yamaha service manual and it appears that my pick up coil is bad. it also appears that to replace the pick up coil i have to buy the entire stator. i was wondering if there was anywhere i could just buy the pick up coil, and splice it into the wiring harness, or if i do indeed need to buy the entire stator. also, where is a good place (price wise) to buy these parts?

  • Hamish

Posted July 05, 2004 - 09:01 PM


Down here in OZ we have a local guy that specialises in motorcycle stator rewinding. I'm sure there will be someone in your area too. Check with the bike wreckers as they are always getting stators rewound. Re the coil voltage, measure from the small wire to the frame. Check ya manual

  • yz400f

Posted July 06, 2004 - 05:58 AM


i measured the three coils and it looks like the pick up coil is bad. i measured it 3 times and 2 of the times it measured out of spec. problem is to replace the pick up coil i need to buy the entire stator assembly. where is a place i can get good prices on yamaha oem parts? my local dealer is known for ripping people off. i need a price on a stator assembly, and quite possible the CDI. thanks

  • yz400f

Posted July 06, 2004 - 01:51 PM


well i have actually determined its either in the spark plug boot or the computer. im going to be replacing the spark plug boot first. are there any good aftermarket replacement computers for the yz400f? how much are they? thanks


Posted July 08, 2004 - 09:27 AM


Dude you are bouncing all over the electrical spectrum here. Your best bet is to take it to a dealer and pay the diagnostics fee. Most places $65.00, you will then know for sure what the problem is and can decide how to attack it. Additionally most diag fees are deducted from the repair if you let them do it. Finding a reputable repair facility is the trick. At the rate your going now you're going to spend a grand on a couple hundred dollar problem.

Bonzai :thumbsup:

  • yz400f

Posted July 08, 2004 - 10:11 AM


i got it running, thanks for the help everyone

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