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The plug does not have to be tight for the engine to run, but if it's not tight enough to prevent leakage, carbon from combustion might fill the threads and lock the plug into the hole. Get it running first and then worry about the plug later.
 

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The plug does not have to be tight for the engine to run, but if it's not tight enough to prevent leakage, carbon from combustion might fill the threads and lock the plug into the hole. Get it running first and then worry about the plug later.
Okay so I’m getting spark now and fixed the stripped stud nut and torque all of the stud nuts to 32 foot pounds and brand new head gasket so no compression leaks out but I’m still getting 90 psi for compression. I’m pretty sure now it don’t start because of low compression what should I do to get it started other than push starting it??
 

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Okay so I’m getting spark now and fixed the stripped stud nut and torque all of the stud nuts to 32 foot pounds and brand new head gasket so no compression leaks out but I’m still getting 90 psi for compression. I’m pretty sure now it don’t start because of low compression what should I do to get it started other than push starting it??
Did you check the compression while holding the throttle wide open? If yes, check the valve clearance and if the valves are right, then push start it - once fired, the compression will probably come up some more.
 

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Did you check the compression while holding the throttle wide open? If yes, check the valve clearance and if the valves are right, then push start it - once fired, the compression will probably come up some more.
Yes I did do that wide open and yes my valve clearance is right but I think I have to push start it like you said and let it warm up and then try to start it with the kill switch it should start. Thanks for the help really appreciate it!
 

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A leaking head gasket will not cause a loss of spark, but it will keep the engine from running. It needs a minimum of about 110 to 120 psi to start - under 100 it would have to be pull or push started
Hello I finally got the bike running it turns on good now and gives good spark and compression thanks a lot for the help!
 

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Now although all the parts you say you installed new are available from Honda, I seriously doubt you spent $835 for parts in your quest to fix the issue. I suspect you bought parts from Amazon or Ebay, so you have a collection of Chinese counterfeit parts on your vehicle, so this complicates matters because instead of troubleshooting the parts that were working prior to the failure, you decided to throw parts at it to see if it would stick.
New member here. Hello all. Glad op got the quad running. Just wanted to point out the above advice for anyone finding tis thread via "no spark" searches. Do not parts swap, especially on electronics. Good parts are too high and the "other" parts are likely bad to begin with. Do not cut wires and jump switches. Go buy a good Fluke multimeter with a min/ max button. (model 110,115,117 are most common range from 100-200 dollars) and study. The meter will last a lifetime of abuse. You can wire your house, diagnose a bad receptacle, fix your car etc etc etc forever. I see them in factory use every day. EVERY electrician I know uses a fluke meter. Find out which part (singular usually) is bad. All the info you could possibly need is online. Download a service manual if you need one and go step by step. People are lucky to have the internet and folks like the above mod.

I own and operate an auto shop. Lately I've taken to more and more atv. I've ridden and worked atv since my first 84 (iirc) moto4. Back before suspension was a thing on quad. Ive owned yamaha since. Never an issue. Dad had an 88 fourtrax 300. I just got it back to running yesterday (no spark.... surprise). I found these threads hunting for a pin out or service manual. But I work on all brands. Honda makes good machines (excluding ES hondamatic models) Worked on them and chainsaw for many years out of my basement. Then built my shop. I believe more money is there to be made on atv than cars actually. People don't question why it took two hours labor to change a 1500 dollar front end in a sxs (thanks polaris) . They do question why it took two hours labor to change a rusted in place 50 dollar wheel bearing assembly on a car.

Parts swapping as we call it is far too common in the auto industry too. Taking off parts without properly diagnosing. Taking off good oe parts and putting on cheap parts store parts. Or worse, Amazon knock off parts. If your going to do that, at least do it one part at a time and if the problem remains... put the good oe part back on. Parts in the atv/sxs world are even more stupid high priced than cars. And with the internet there is no reason to not study up. Back pre internet we did have to do some switch jumping and such. Lol

On cars I've fixed thousands of dollars in damage caused by cheap sensors that most likely replaced parts that weren't bad. Cheap wheel bearings, axles, interior parts, pumps, racks.... go for it. But anything electrical (or a carb) do not.
 

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HelloI finally got spark on my bike but I have a question I put a longer stud nut in my cylinder to replace the stripped one but now I don’t have space to torque the spark plug im getting spark but would the bike start with the spark plug loose just tight a little bit or would I have to tight it to it’s torque?? Because I left it loose tight it wit my fingers and the bike wanted to start and was shooting blue smoke from the exhaust ???
So what ended up being your cause of no spark? Currently dealing with the same issue on my bike
 

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So what ended up being your cause of no spark? Currently dealing with the same issue on my bike
Well, it's been two months since Cristofer631 was last seen and it looks like he's not going to answer, so let me see if I can help you.

Do you have a peak voltage tester? I presume not, so we'll do this the hard way. There are only 4 main components of the ignition system of the TRX400EX. Excluding wiring - the stator, the rotor (flywheel), the CDI unit and the coil. The spark plug cap and spark plug are components, but are actually terminations and while important, are not part of the SYSTEM. (the battery is just for lights and to run the starter motor).

First step is to disconnect the kill circuit - disconnect the black/whte wire from the CDI unit - if spark is restored, just find where the black/white wire is shorted to ground - if still no spark, then we start checking connections and if your is later than 05, the there is another component as 05 and later had reverse and a reverse limiter.

Product Rectangle Circuit component Slope Font
 

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@Cristofer631 @here to help this forum has been a great help with certain aspects of the diagnosis.

IM in the exact same predicament as chrisofer631 .. no spark changed parts ect

My crank and tdc is fine. Please can i have assistance on the testing of the exciter wire red and black wire would this need testing at the CDI or as soon as it comes from the stator .?

Thanks in advance
Ps trx 400ex
2004
 

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IM in the exact same predicament as chrisofer631 .. no spark changed parts ect

My crank and tdc is fine. Please can i have assistance on the testing of the exciter wire red and black wire would this need testing at the CDI or as soon as it comes from the stator .?

Ps trx 400ex
2004
Testing the exciter coil - blk/red wire to ground - should test appx 45v peak - you need a meter with a peak voltage function or a PVA (peak voltage adapter) for a standard DC voltage reading
 

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Thanks for the quick response. Okay so i have this multimeter (TIS 258 Digital Multimeter With Temperature Probe)
Unfortunately i dont think this measures peak voltage. Ill buy a adaptor. Ive dont a ac voltage check with the above multimeter, red probe on the black and red wire and the other to ground .. when i crank the engine i get 50acv
Ive checked continuity of all the ground points and all is fine.

Is there any checks i could be doing in regards to voltage checks with my current multimeter to dignose the issue before i buy a new meter.

thanks again
 

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Thanks for your message. Ill look at buying one asap .. what doed the peak voltage symbol look like. My understanding is that it gives a min and max output.. am i correct with this ?
 

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Can't say for sure - each mfg. uses their own marking, but generally min-max is the indication for measuring transient voltages
 

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Thanks for your response... ive now ordered a peak voltage adapter. Ive spend the whole day going through my wiring ensuring the issue has nothing to do with the clutch or neutral switch. They seem fine.(Found a wiring diagram online)

I noticed you said to check for continuity from the pulse wire. I guess the purpose of this test is to determine if the wire coming out the stator to the cdi is fully connected to the CDI with no breaks. No issues here

Im wondering whether the pulse wire is correctly gapped when i replaced the stator. I didnt recall seeing any room for ajustment they just bolted in.

Could i do simple resistance check when cranking the engine to see if i get a fluctuating reading from the pulse wires as it spins the crank

Lastly as im inpatient i tested the ac volts with my meter again on the red and black wire (exciter) And got a steady 70 when cranking

I know its not the proper tool but delivery for this is around a week.
ive also tested the black and yellow wire into the spark coil and the ac reading seem low. Does this seem normal.

thanks
 

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Normally, I would say no, but if you use an analog meter set on the AC or DC scale and see movement of the needle it is usually a crude indication of a trigger pulse - then the only thing left is the CDI unit, coil, spark plug cap and spark plug.
 

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Hi,

So today my peak voltage adapter arrived.

These are the checks ive done so far
Exciter wire
Red probe on black/red wire
Black probe on green/ white wire.

Set the multi meter to dc voltage
My reading i got when cranking was 116.3dcv
I believe this is okay.

Next test i did was ignition pulse generator.
Red probe on blue/yellow
Black probe on green/white

From the front of the atv i get no reading when cranking 0.00

From the back where the wire comes from the stator i get 2.78dcv unplugged from harness and checks stator side)

Now i find this very odd. I have a new loom on the atv and have checked for continuity from the green and white wire going to the cdi plug to the plug on the stator all is fine.

Ive also check the continuity cdi plug and rear of the blue/ yellow all seems fine

Im not sure if 2.78dcv are correct but i definitely know that having nothing at the plug end by the cdi is wrong.

Any advice would be appreciated

Thanks
 
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