XT 500, no spark... help???

23 replies to this topic
  • Stites

Posted December 03, 2006 - 08:03 PM


First off, hey y'all, and thanks for having me.

I've had for several years now a CDI-equipped XT 500 that was once a flat-tracker at Daytona, and is now my personal horse. Since I've had it, I've swapped the OEM coil for a Ford truck coil with Chrysler external resistor(when my original one went out, I didn't wanna get raped by the Yamaha shop in town for a replacement), and have had many, many long hours of good riding on it. The bike sat for a year and a half while I went overseas in OIF 1, and when I came home, I changed the oil, gassed it up, and was riding on the 3rd kick. All in all, this has been such a dependable and STRONG bike that, despite its hideously repulsive appearance(my fault), I can't bring myself to get rid of it!

And here we are at today. I just finished plumbing a new 1 3/4" exhaust into a car catalytic converter mounted in the stock location(had a headerpipe swung down under the peg and into a megaphone straightpipe... LOUD) to make it more woods-friendly, checked the spark, and found none. I've checked out the magneto/stator thingy in the flywheel, all wires, the coil resistor, and even bought a new coil to make sure that wasn't the issue. Still no spark, not so much as a jolt to the finger when I held the plug wire. All I can assume is that the CDI box is bad, so before I drop money on another'n, I'd like to know if there's anything I may have missed. Also, if I do need a new CDI, is there any other bikes that used the same box? I'd rather not have to get raped by the Yamaha shop(would you believe they want $5 for the same spark plug I got at Carquest for $1.89???), so I'll be hitting up a couple of bike boneyards in the area.

If it helps, I do know it's a NipponDenso box, and I have the part number at work if needed. Thanks for y'all's help, I'm hurting for a good ride!

  • Stites

Posted December 04, 2006 - 12:44 PM



Oh, the CDI number is NipponDenso 3H6-50.

  • beezerjoe

Posted December 05, 2006 - 11:33 PM


Hi there Stites I just helped out a friend of mine with his SR dirttracker that had lost spark.On this bike it had mototech ignitionwe removed it and put the SR ignition back on it ran great for two races then lost spark.We tested everything with a meter as per the book specs and it all seemed fine.We then changed black boxes,coils only to find the stator in the mag had taken a powder so we replaced with a good used stator and the spark came back even though the old one tested ok.If you find that you need to replace the cdi box Wayne Gum sells on ebay what he calls a HYPERPAK which replaces the stock cdi box and only costs about $150.His company is called electronics reseach and design.I personally have one of these units on TT600 and it seems to be fineand at half the cost is a pretty good deal.Also check your wiring and key switch tomake sure nothing is dirty disconnected or grounded out.Hope this helps you out.

  • Stites

Posted December 06, 2006 - 10:49 AM


Thanks, beezer. I 've been running a questionable flywheel for many years now, after I cleaned the stator and forgot to tighten the screws before putting the flywheel on... that was ugly. I've done similar checks on the stator, and it has continuity, but turning the flywheel with a drill at well over kicking speed produced only .6V the way I checked it, so I'm not really thinking the CDI is the culprit anymore.

Do you recall right off the proper way to test the stator? I haven't had my Clymer book in years. As for wiring, all is cleaned, and the key ignition was long gone before I got the bike. So I'm at a standstill till I can get this gremlin figured out.

  • beezerjoe

Posted December 07, 2006 - 12:23 AM


Hey Stites Joe here again.The only way I know to check the stator is with a multimeter.You have to disconnect the stator from the black box and measure the resistance between the circuts coming from the stator.I don't have the specs or wiring color codes with me at this point in time but my friend with the SR powered dirttracker does.I will suggest either a Hayne's or a real yamaha service manual.I personally don't care much the Hayne's but they do have a fair amount of technical info compared to most.The SR we just replaced the stator in when checked appeared to be ok we also checked the good used replacement stator and it showed to be the same as the inoperative one we took out by the readings on the meter so whatever caused the first one to fail is a mystery.If it turns out you need a stator I would get ahold of Mark at THUMPERSTUFF he probably has a good used one in his pile of parts.Let me know how it turns out and don't let that ugly bastard keep you down:thumbsup:

  • beezerjoe

Posted December 07, 2006 - 12:37 AM


I forgot to ask if it was a late cdi SR or XT stator or if it was a TT stator for points that has been modified to cdi.Several of the local racers have converted their TT's to the ford ignition coil but still use the original points for the trigger.The SR we were working on had an old mototech cdi that used the TT stator but it was old and breaking down so we put the stock SR system back in.

  • beezerjoe

Posted December 07, 2006 - 06:44 PM


Ok i did some digging and found the values for the stator they are as follows:
  • ohmmeter set at RX10 high speedwinding white/red to black = 16ohms + - 10% and low speed windingWHITE togreen/black =91 ohms + -10%
  • meter set at RX100
  • meter set at RX 10 charging/lighting coil BLACK to WHITE = 0.28 ohms + - 10% BLACK to YELLOW 0.24 OHMS + - 10%
charging coil high speed winding RED to BLACK = 390 ohms + - 10% low speed winding BROWN to BLACK = 381 ohms + - 10%
to check the ignition coil disconnect the coil from the harness and check the primary windings with the meter set on RX1 attach to the small wire and to the grounded part of the coil value should be 0.98 ohms+ -20% to check the secondary go from the grounded part of the coil to the sparkplug wire with meter set on RX100 the value should be 14K ohms+ -20% if any of the valuies do not match the stator or the coil will need to be replaced.This is for 1980 and later xt 500 models.Happy hunting.:worthy:

  • beezerjoe

Posted December 07, 2006 - 07:12 PM


It's funny how every couple of minutes I have another brain storm.Since from what I can see on your signature it has a 77 engine this should have been originally a points/condensor ignition and your stator should have only 4 wires coming from it.There should be white and yellow wires for charging and headlamp a blue from the neutral safety switch and a black/white wire for ignition.The book I have is a clymer and does not give a test procedure for the stator.What I have done in the past to check a dirt simple system such as this is to unplug the stator from the harness plug a separate wire into the B/W wire at the stator plug end and spin the engine with the bared end of the wire just lightly dragging on the rotor and see if if generates sparks,if it does then your ignition coil in the stator is probably good and the problem lies elsewhere.I just had another thought your neutral switch maybe grounding out and killing your ignition system if the blue wire is still there disconnect it from the engine end by the shifter or eliminate it completely and see if the spark returns.

  • Stites

Posted December 08, 2006 - 07:05 AM


Just... WOW.

Joe, I do appreciate the tips and info you've offered. As for the stator, it's all late model stuff, so I'm wondering now if I have a later engine than I thought, or the previous owner did a thorough CDI conversion. If it helps any to ID the engine, the numbers on the cases are 3H6-001729(1981???).

I put my old stator and flywheel back on last night and checked voltage output on AC... DC showed .4 volts max with a drill turning the engine over at about 350 rpm. However on AC settings, the brown wire showed 23V, and the red(or pink, I can't tell) one showed 38V. Now this is a DC ignition system, right? Could there simply be an inline diode that needs replaced?

So the Ford coil is a favorite among racers, eh? That makes me feel better. Now I may be crazy, but I'd like to see if a GM HEI module could take the place of the CDI box.

  • beezerjoe

Posted December 08, 2006 - 06:27 PM


From what I can gather the ignition system is A/C although it does have a charging system that is separate from the ignition system that does D/C.As far as your engine serial number I did alittle checking and found it to be a 1980 XT500G model.If you can get that GM module to work that would something.Glad to help out let me know what you find.

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  • nsman

Posted December 09, 2006 - 01:31 PM


All north american models to 1981 h models xt500 were equipped with points ign,all sr 500 came with cdi.

  • scooter-mike

Posted December 09, 2006 - 01:56 PM


I disagree with that the 1980 G XT and 1981 H XT both had cdi units, 1976 through 1979 had points and all tt500's had points,(1976-1981) according to yamaha's parts catalouge.

  • beezerjoe

Posted December 09, 2006 - 06:25 PM


I disagree with that the 1980 G XT and 1981 H XT both had cdi units, 1976 through 1979 had points and all tt500's had points,(1976-1981) according to yamaha's parts catalouge.

You are right Scootrmike the last 2 years of production the XT was equipped with a cdi all TT's came with points and as Nsman said all SR's had cdi.

  • bulabula

Posted December 10, 2006 - 09:40 AM


Years ago, my brother got rid of a TT600 basket case that had a bad CDI box.

Knock on wood with my XT's CDI ignition; but what's available now and where, should my CDI take a dump?

  • beezerjoe

Posted December 10, 2006 - 11:32 AM


Years ago, my brother got rid of a TT600 basket case that had a bad CDI box.

Knock on wood with my XT's CDI ignition; but what's available now and where, should my CDI take a dump?

Check on EBAY for a unit called HYPERPAK.I got one for my TT600 before the overhaul started and it seems to work fine but my engine had unseen damage internally which kept it from running properly.The cost is about $150 which is less than half of what yamaha charges.They are built by Wayne Gum at electronics research and design in New Zealand.He also makes cdi boxes for SR's XT's and Suzuki gsxr's and the like.

  • nsman

Posted December 11, 2006 - 11:56 AM


Scootermike and Beezerjoe,
You guys had me second guessing myself.I have checked today at work as I am a Yamaha dealer in Canada .The 1981 xt500 Canadian model code 4t9 did infact have points ign....nsman

  • bulabula

Posted December 11, 2006 - 06:30 PM


Scootermike and Beezerjoe,
You guys had me second guessing myself.I have checked today at work as I am a Yamaha dealer in Canada .The 1981 xt500 Canadian model code 4t9 did infact have points ign....nsman

What is the code 4t9? Is that part of the VIN? I was just curious because the VIN's on my two Yamaha's are nowhere near being close for being "almost" identical.

  • nsman

Posted December 11, 2006 - 07:10 PM


4T9 is the model code as in the first three # of the serial number.The number on the frame for the 1981 Xt500H cdn model would be something like 4T9-0001234 .It is interesting to note that the USA version of the XT500 has a model code of 3H6 and has a cdi ign.Up untill yesterday I was unaware that the CDN and USA models were different.Guess there is always something new to learn!
I have a 1978 and a 1979 Sr500 and they both have the cdi system.

  • beezerjoe

Posted December 11, 2006 - 08:16 PM


I found a site that has V.I.N number prefixes posted.I don't know how to post a link so I'll type it out http://www.siue.edu/...SR/sercolor.htm What I found for number prefixes are 1980 XT500G 3H6 SR500G 3H1 TT500G 1T1 and 1981 XT500H 4R9 SR500H 4R8 and TT500H 2Y0 .Nsman the Canadian models may have not been subject to the same requirements as U.S models but I can't say for sure.Because of our emisson laws for road going models they may have mandated electronic ignitions.This also might the reason for for the different numbers on the engine and frame.

  • Stites

Posted December 13, 2006 - 08:07 AM


Welp, I still have no spark after how long? I'm beginning to think the CDI is the culprit once again. I've tried every way possible to get fire out of it, and still have nothing. Does anyone know if you can check one with a multimeter? And how to do so if you can?


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