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AdamsZ

87 TRX125 - No Spark

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Hey Guys, I’m an experienced mechanic and have always been quite successful with electrical and electronics. I got a 1987 TRX125 for trade for some labor. This quad has not been modified and I was told that it just stopped running one day. This thing has no spark. I will try to give you the information  that I have collected. I have replaced the coil and cdi and spark plug. I have checked all the wires for continuity from end to end. Pulled the cover and ohmed out the stator.

The blue/yellow wire at the cdi has 300 ohms to ground and fluctuates while cranking

The black/white wire is open and grounds when using the kill switch in either direction

The gray wire has 12v with ignition on 

The black/red wire has 55vac cranking with the starter, 125v when pull starting

The green/white wire is open to ground and no voltage

The black/yellow wire at cdi no voltage, open to ground

The black/yellow wire at the coil has -4vdc key on and cranking

the dark green wire at the coil is grounded

i have grounded  the reverse switch and left it open and it makes no difference

The neutral light is on and the reverse light is out

I’m guessing I’m missing something simple or do I have a bad pulse generator? 
Thanks in advance for the help

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Moved this to it's own separate thread since your 87 is a bit different than the 85-86 models.

 

Welcome to the board!

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Welcome to ATV Honda @AdamsZ!

 

I would like to help but I don't have a wiring diagram for the 87 TRX125. I have a couple general tips that applies to all Honda ATVs though:

  • China aftermarket ignition/electrical parts knockoffs do not work on Honda's. So if any of your ignition parts are aftermarket, then the ATV cannot be diagnosed & repaired. Solution: Put all of the OEM parts back on it and then diagnose it.
  • If the CDI have failed you can usually revive them by heating in an oven at about 190 degrees F, for about 30-40 minutes.

Do you have a wiring diagram (or a service manual PDF) that you can share?

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This what I’ve been working from. I will try the oven trick. The cdi I bought is a China knockoff.

8C9514A8-BDED-4D34-8631-53B6ABAC769F.png

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Thanks! I found another diagram after scrounging around the 'net a bit more.

 

TRX125_1987_wiring.jpg

 

I would put all of the OEM parts back on it and then diagnose the ignition again from scratch. The OEM CDI should be labelled CI540 (if the model number has not rubbed off). Link here:

https://atvmanual.com/honda/honda-cdi-identification

 

Each of the Ignition component resistances should measure like so (Link)

 

ing-specs.png

 

Let us know what you learn as you go if you can. Hollar if ya have any questions!

 

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I put the cdi in the oven and that didn’t work. That looks like the same schematic I’ve been working from. I watched a video from RM stators and he said tha the cdi is either ac or dc not both. Can’t understand why the gray wire would have 12v on it and 55vac on the 

black/red wire if you only need ac or dc. I’m currently looking for an OEM cdi

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3 hours ago, AdamsZ said:

Can’t understand why the gray wire would have 12v on it and 55vac on the 

black/red wire if you only need ac or dc

 

The TRX125 have AC-CDI ignitions which operate on AC voltage supplied by the Exciter coil. The grey wire at the CDI has DC voltage because it is tied into the black (+) battery voltage wire with a resistor near the neutral & reverse indicator lights, so voltage on the grey wire is normal while the trans is in neutral and the ignition switch is on. Voltage on that grey wire should not exist while the trans is in reverse though, since the reverse switch grounds that voltage. So the grey wire provides a sense circuit to the CDI. I circled that resistor in the diagram below.

 

TRX125_1987_wiring-resistor.png

 

 

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Here is an update. I attempted to wire the Chinese knock off as an ac only cdi. Still no spark. I don’t mind spending $130 for a new cdi but I don’t like to throw parts at something. 

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Yup throwing money at problems usually turns out to be foolish. Does the exciter coil, the pulse generator and the ignition coil Ohm out to specs when each is measured?

 

ing-specs.png

 

The ignition switch and the kill switch in an AC-CDI ignition system shut the motor off by grounding the ignition coil primary voltage out. So if the exciter coil, pulse gen & coil ohm out check the ignition & kill switches again. Let us know what you find out after rechecking those.

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Ok, I fooled around again this morning. Made up seperate jumper wires to the components. Eliminated most of the harness, eliminated the switches, coil ohms out at .5 ohms. Is it possible for the trigger to ohm out and be bad? 

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2 hours ago, AdamsZ said:

coil ohms out at .5 ohms

 

Which coil, the exciter, pulse gen or the ignition coil? Whichever it is .5 ohms is not within spec for any of the three...

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The ignition coil that came with it is .5 ohms, the one I bought is .8 ohms. Everything else is within specs. I’ll see if I can find another ignition coil

 

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5 hours ago, AdamsZ said:

The ignition coil that came with it is .5 ohms, the one I bought is .8 ohms.

 

Both of those ignition coils are china garbage I'll bet ya. OEM Honda parts are the only parts that work on Honda's... that statement will always be true.

 

Glad ya finally found a fault (other than the suspect CDI). 🙂

 

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OK, the plot thickens! I replaced the ignition coil with a known good OEM Honda coil with .3 ohms. Still no spark. 
Todays numbers with all wiring harness and switches removed

Pulse generator 298 ohms

Exciter coil 226 ohms

Ignition coil primary .3 ohms

Ignition secondary w/o cap 3749 ohms

Time for a cdi? Where to get one? since they are obsolete 

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Yup, but lets do one more test before you shop for a CDI. Plug everything back in, then unplug the Black with White stripe wire at the ignition switch and unplug the Black with White stripe wire (kill switch) from the handlebar switches. See if it has spark with those two wires unplugged. If not, its looking like shopping time...

 

wiring.jpg

 

 

 

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I ordered a new cdi box today, guaranteed to work. I asked to return the Chinese cdi box and they refunded my money without returning it. Makes me wonder why they would do that unless they know they’re junk. 🤷‍♂️

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That china CDI you were sold is not even an AC-CDI, It is a DC-CDI with a harness plug put on it to match your harness. The china scammers only sell three different CDI versions (30+ different harness connectors "fit all" ATVs & motorcycles tho, haha) and all three are incorrect for the early Honda AC-CDI ignitions.

 

In fact, the CDIs that they sell to replace the early Honda DC-CDI modules actually fry OEM ignition parts the moment someone plugs one in. We have diagnosed quite a few of those... So yeah, they don't argue with ya if ya file a claim, they refund right away. They make lots of money on CDIs that don't match the application because most folks don't bother to attempt a return for a measly 15-20 bucks or so, on fleebay or scamazon.

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I wonder how they got a 98.2% positive rating on eBay. When I went to my account it’s as if the transaction never occurred. 
 

ive been following the schematic and I was wondering if anyone has a pin out diagram? Is it the same as most of the ac-cdi’s?

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10 hours ago, AdamsZ said:

I wonder how they got a 98.2% positive rating on eBay. When I went to my account it’s as if the transaction never occurred. 

 

Two reasons... first reason is eBay removes a portion of any negative feedbacks a seller have recently acquired every 30 days. That's eBay policy... they do it for every seller to make eBay look like a safe shopping experience. It's dirtbag behavior though, because eBay destroys buyer trust in doing so.

 

Second reason, once a seller accepts a return and/or refunds a buyers purchase that transaction is null and void. So a buyer cannot leave any feedback for a transaction that did not complete.

 

10 hours ago, AdamsZ said:

ive been following the schematic and I was wondering if anyone has a pin out diagram? Is it the same as most of the ac-cdi’s?

 

Yep, almost all AC-CDI ignition CDIs are wired up the same. Yours differs only by utilizing a battery voltage sense circuit that gets grounded whenever the trans is in reverse. Most other early Honda's do not have that reverse sense circuit.

 

So if the seller would have sent you an AC-CDI (rather than a DC-CDI) you could have wired it up correctly and it would have likely worked for a while.

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While I’m waiting for my cdi to arrive, I’m getting ready to reseal the magneto cover. When I pulled the cover the shafts and gears ended up n the floor. According to the parts diagram #8 is a collar that slips on that shaft. The collar fits very loosely on the  shaft. Do I weld it up and redrill it, or discard it?

3BB5BAC1-B5BA-4257-8E89-04B29C09D502.png

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Is that a spacer, or a reduction gear shaft support bushing? If it is just a spacer for the reduction gear I'd leave it alone. But if it is a support bushing for the shaft then it should be replaced, not repaired.

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The part description says “collar 10x11”. The shaft is supported by the crankcase and the left crankcase cover. I’ll check it next time I go out to the shop. 

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It's just a spacer for the gear then, doesn't matter if it fits the shaft loosely. It's ready to assemble once ya get the gasket eh?

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I had a chance to plug everything in and I have spark. Now to put the side cover back on and start this !!! Glad I got this for almost nothing cuz I have a ton of hours messing with this thing. 

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