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Socalmotorider

Need electrical help on a yz400f

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Thanks to Tim (Vacman) i have a project bike hoping to get back on the saddle.

It's a 1999 Yamaha YZ400F and does not want to spark/fire so i downloaded the manual to check voltage etc. and here is what i found.

First i checked the obvious getting fuel,stop switch and spark which i am not sure but the spark is there but looks pretty faint but seems to jump across.

Next i broke out the meter to test the coil and CDI and here are my findings

CDI magneto inspection read 282 should be 248-372 GOOD

Source coil 1 resistance read 332 should be 720-1080 BAD

Source coil 2 resistance read 46 should be 44-66 GOOD (barely)

Secondary coil resistance read 11.57 should be 9.5-14.3 GOOD

Ignition coil jumps around ALL over the place and should be 0.20-0.30

Sooo hopefully some one has a better idea than me on my next step before i start throwing money around i don't have Haha Thanks in advance

Also bike does appear to have a aftermarket stator and i am guessing it's either a bad coil or stator ???

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Coils rarely fail, Yamaha CDI's were pretty good as well. Searching Ebay, it looks like you can buy a coil, stator, wiring harness and CDI for under $100 for used parts. At that price, you can't hardly go wrong.

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Wow awesome find, I always seem to forget about Ebay Haha think i will order all of the above just to be safe for that price although i would like to upgrade the Stator (or hope the after market one is good that's in there) as i would like to eventually get it plated so need to run a headlight.

Thanks i owe you a beer :)

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If you want to run a headlight you could try to find a WR 400 or 426 stator, I bet they could be located at a decent price.

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Before you go swapping YZ for WR stators do a little reading at Thumpertalk. I think the crankshafts for certain years are different and some YZs won't accept/ cannot get higher output stators without swapping to a WR crankshaft.

One reason I went with the FI YZ was the stator produces enough excess power to run lights for a future street legal project.

Good luck with the troubleshooting.

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It already has an aftermarket stator so hopefully that's not the issue. Or if it is at least it can be replaced with the same thing. my money is on the coil as I also tested it as bad. If I had more time and motivation I would have replaced the coil and sold it for a bunch more! :)

Lol, glad it went to a good home. Look forward to riding with you soon, Chris! Call or text if I can help.

Tim

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The older YZ/WR 400/426 can accept either stator. Not sure if the rotors are different. WR426 stator is the best one, more output than the 400.

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Thanks for the info. guys and i am pretty sure it's the coil as well so think i will start with that even though ricky stator seems to think its the stator.

And nice meeting you as well Tim and hope you enjoy your new toy in 10 day's :) i look forward to riding again hopefully soon.

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According to Ricky Stator source one coil which is way low means Stator and others have mentioned the bad reading i am getting on the Coil itself is because the number is so low it's hard to get a accurate reading unless using a "real" meter so what do you guys think ?

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I haven't seen a bad coil on a motorcycle newer than 1980, and I have worked on a few. There's a first time for anything, though.

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Ok so a little update today. I had some time in between doing 10 other things and first of all started with cleaning the carb. which was surprisingly dirty with the pilot being almost completely clogged and when i put it back together after a few kicks it actually started for about 2 seconds then after trying for another hour i could not do it again so i went and found a new coil and plug,installed them both and spark looked way better but still would not fire so i then pulled the plug right after trying to start it for a while and the plug was not even wet nor smelled of gas so ?????? i had to get ready for work so had to stop there but any more suggestions would be appreciated. Thanks

Chris

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Clean the carb again. I had a TTR that I pulled the carb a half dozen times before it would finally run right.

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Check that the float valve is filling the carb.

Sometimes the float valve gets sticky and won't allow fuel flow..

also clear the air director.. with compressed air and carb cleaner.

plus pull the air/fuel screw.blast that idle circut with carb clean and compressed air. Return the mixture screw to the factory setting.

Personally I would just go buy a new pilot jet.. $5 motoworld... maybe the next size up....

Always put in a new pilot jet if you want it to kick right over and idle smooth.

If you squirt a few drops of fuel into the plug hole, then get the same results (runs for 2 seconds) then do the carb again or at least switch the petcock to the reserve position.

there's a 100 you tube videos on how to do a carb.

Also on that bike you can bypass the idle circuit by pulling the choke plunger .

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If the carb got that dirty it would certainly explain the issue. I bet they got dirt into the tank when they filled it.

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Sharing some personal grief. You may want to look into the valve timing. I had a 98 or 99 YZ400 and the camshaft gear is pressed on the camshaft... the cam gear spun slightly on the shaft and would not start... took awhile to find. :weird:

Once you have proven your ignition/spark situation is ok... might look at TDC (top dead center) and valve position. Hopefully you do not have the same issue!

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Sharing some personal grief. You may want to look into the valve timing. I had a 98 or 99 YZ400 and the camshaft gear is pressed on the camshaft... the cam gear spun slightly on the shaft and would not start... took awhile to find. :weird:

Once you have proven your ignition/spark situation is ok... might look at TDC (top dead center) and valve position. Hopefully you do not have the same issue!

Thanks for the info. and i hope it does not turn in to that although it is starting to look more serious than i hoped for but we will see.

Finally had a chance to mess with it a little more today and so far pulled the plug,poured a little gas in then replaced the plug and still not firing so not sure of my next step Haha think i will have a beer and think about it :)

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So hooked up the meter and rechecked everything, got the same readings i got with the stock coil so ruling that out.

Leaning towards a bad stator,timing off or valves need to be adjusted.

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Timing check and valve check/adjust aren't difficult. Might be good to do it, just to rule it out.

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Timing check and valve check/adjust aren't difficult. Might be good to do it, just to rule it out.

Maybe for you Haha I did assemble the motor in my drag car so am somewhat mechanicaly inclined but am intimidated of a motorcycle engine for some reason Lol

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Well there's only three things that will make your bike run...

1.spark

2.fuel

3. Air

The same three element that cause a camp fire to burn. Figure out which one your lacking and boom your off to the races again.

If you can turn a wrench , and want to pull that valve cover off, PM me. if your not to far out of my way i can stop by and slide my feeler gauge under the cam, after I get done servicing these other bikes..

If you can catch me while im out in the service truck.

Or keep posting and working towards it...there's alot of gear heads on here that can help .

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Well there's only three things that will make your bike run...

1.spark

2.fuel

3. Air

The same three element that cause a camp fire to burn. Figure out which one your lacking and boom your off to the races again.

If you can turn a wrench , and want to pull that valve cover off, PM me. if your not to far out of my way i can stop by and slide my feeler gauge under the cam, after I get done servicing these other bikes..

If you can catch me while im out in the service truck.

Or keep posting and working towards it...there's alot of gear heads on here that can help .

Thanks that would be cool, I have the day off and am getting ready to head out to the garage in about a hour to mess with it. I have most of the stuff off the bike now so just need to pull cover off. It doesn't sound to difficult so think i will try to check them myself but appreciate the offer although if you happen to be in the Santee area feel free to stop by and help/show me what to do Haha I don't mind doing the work if someone can point me in the right direction. Thanks again to all for the advise

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Don't be intimidated by a valve check. I'm sure there are probably youtube videos if you search. Adjusting the valves, that's a little bit more involved but the basic check is simple. Let me know if you need a hand. I have valve shims if it needs adjusting.

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If it doesn't have spark and the stator is aftermarket I can tell you that's very likely the problem. As others have noted, the ignition parts that live outside the motor rarely fail. Aftermarket stators are sometimes tough to diagnose because they're often wound with much different ohm values than the stock stator which makes the value ranges shown in the service manual almost worthless.

If you end up replacing the stator and go the WR route you gotta get the WR flywheel and CDI module for it to work. The 00-02 WR stator makes more lighting coil power than the 98-99 stator so the newer ones are better. Also the CDI needs a small wiring mod to plug into the YZ harness but it's easy.

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Guest Big dog

I have wired two staters to charge batt. Hav illustration from baja desighn yz 400f and wr yz 400f

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