1984 yz125 no spark!! plz help

[mxken9]

i have a 1984 yz125 when i was idleing in the yard it stald and wouldnt start back up. i have tryed replacing the coil and 3 different plugs in it and still no spark. does anyone know what it could be???? any help would be greatly apriciatedcuz im going nuts trying to find out what it is :bang:
thx
ken


oohhhh p.s it aint fast without mixed gas

 

[CRazy250]

are you serious? please run mixed gas. check for broke or bad wiring, kill switch and check ground wire

 

[Glamis!]

I have a 76 or 77(Got from a friend, title was lost, checked websites and serial number came back as different years on diff ones) yz125 with the same problem. It started all right, and got proggressively worse, we had to pull start it at the end, then after I shut it off, came back to start it and wouldn't go. We checked, it had no spark, so we got a new coil, new plug, new plug wire. We have been thinking it is the CDI box, but I am really not sure. So it could be the same thing.

Josh

PS You really should run mixed gas, but I don't think that effects spark.

 

[wirefryer#85]

If your running it without mixed gas, it probably doesn't have enough compression left to start

 

[kx125412]

If it starts then after it warms up it dies it could be the stator. I've heard of stators warming up then dying but once they're cold again the bike fires up.

 

[chicoman]

Who said anything about not using mixed gas?

 

[apb]

Who said anything about not using mixed gas?

did you read the full [original] post?

 

[chicoman]

did you read the full [original] post?

I think so, if your refering to;

oohhhh p.s it aint fast without mixed gas

then I dont think he ment that he was running straight gas. It's an old saying "It aint fast unless it takes mixed gas" meaning it aint fast unless it's a 2 stroke. It's an old saying, dating back to when 2-strokes had way more power than a 4-strokes.

 

[apb]

Oh, I hadn't heard that saying before -- maybe mxken can clarify for us!

 

[thorman75]

First thing is eliminate the kill switch from the circuit. Then you'll need a Ohm meter to check the resistance of the pulser and exciter coils. If they check out, IE not a open or grounded circuit its the CDI box.
A factory service manual will give you the resistance numbers and which 2 wires to probe.

 

[chicoman]

If your stator passes the resistance test it doesn't necessarily mean that it's good. Most OHM-meters only use a few volts to check resistance, this isn't enough to break down weak insulation.

 

[thorman75]

OK, then how does he test the coils?
With my unit I would replace "Dosen't necessarily mean" with "I'd be willing to bet".Besiders if its an open even a $5.00 meter will show than.I know the electricians I used to work with used a Megger to find leaks in electrical systems due to bad wiring insulation.But that was 3 phase 440V systems, usually a leak arced out tripping the breaker or catching something on fire.( Aren't Steelmills exciting!)
Anyway its better than replacing the whole system 1 piece at a time till you find the fault.

 

[chicoman]

Actually, 440V isn't too far off what a stator coil can produce, and yes a Megger would be a better choice, but probably not available. I wasn't knocking the simple resistance test, in fact it's the first I do when I suspect a bad stator, I was just saying it's not as conclusive as some people think it is. Place something that vibrates against the coils while doing the resistance test, this will show any intermitant faults. One test he can do (if it passes the resistance test) is to dry out the stator really well with a hair dryer. Then pack silica beads (most electronic goods come with a package of these) around the coils for a few days to draw out any moisture that's worked it's way into the windings. If it works after this then there's your problem. Generally speaking: When CDI's start to go bad they usually work when cold but start to fail as the bike gets hot. When stators start to go bad it's usually the opposite, it's a pita to get the bike started but as the windings get hot and dry out they start to work better.

 

[thorman75]

Yeah I should have mentioned that those 440 systems at the mill had cables as big around as your arm and the motors were pulling god only knows how many amps. I know that in the electical sub tunnels, when we were in there, there was so much energy being transferred all the hair on your body would stand up.

 

[chicoman]

An 800 hp motor would Probably draw about 500+ amps from a 440V 3ph supply and would most likley be connected with 750 - 1000mcm copper. I did a co-op at a steel mill, never had my hair stand up though. The mill I was in had mostly DC motors (easier to control the speed) Some of the old guys would open up the knife switch to the armature and use the arc to light their smoke. crazy.

 

[chicoman]

BTW 1000mcm = 1" diameter, which is smaller than my arm.

 

[thorman75]

Well I worked at the 2 largest steelmaking furances in the northern hemisphere(Inland /Mittal steel #4 BOF)30 years.
. We had 5 cranes that were rated at 450 tons(900,000 lbs) on the main hoist, 100 ton aux, to tip the ladles and 50 ton pony hoists.They were all DC.I was a mechanic, to change the main hoist cables it took 4 spools of 1 1/4 cable 1165 foot long. Most people have never seen equiptment this large.Trust me, the feeds were as big as your arm.The ID fan motors in the pollution control area were 6 foot tall and probably 10 foot long.If i remember correctly they were 1000 HP. We had 4 of em and what a job to replace and align.

 

[chicoman]

Sounds like a woman I used to date.

 

[mxken9]

o srry the it aint fast without mixed gas is a quote from like the 1980's. i just put it in cuz im a die hard 2 banger fan. well ive changed the cdi the plug again and its got great compresion. it will spark but it will start as a weak spark then spark wicked good then just stops. i also have changed my kill switch. well if anyone has some ideas i can try them cuz i have a full parts bike

 

[chicoman]

definitely change the stator if you have a spare.