Bike won't start- suspect ignition problems

[Power93]

Hi guys, I'm new to the forum and new to pitbikes too.
I picked up my first pitbike the other day for next to nothing (2013 assassin 125cc). Guy who sold it barely rode it and couldn't start it when I went to pick it up so I got an even better price. Anyway, about the bike.

Couldn't start it so checked the plug. Was black and ****ty so replaced it. Still didn't start so took the carby apart and found it to be clean and jets clear of debris. Compression tested it and measured 110psi cold (used a ****ty universal fitting one I had which didn't fit well so could be higher).

The new spark plug and also the old one after I cleaned it had a weak spark. But, I was able to hold onto the plug and only feel a tiny little jolt. I'm a sparky but have no experience with auto electrics... I thought spark plugs were supposed to put out a thousands of volts and that definitely wasn't even close.

This leads me to believe it is the ignition system at fault. So, before I go out and buy a whole new kit, is it worth trying to get an individual component, if so which is more likely to be the problem?

Thanks heaps for the help!

 

[Blender]

Welcome to MiniRiders Power

have you checked your lead for kink/burns ? You have the lead attached to the coil tightly?

Does your lead have a metal cap? if so, make sure its not touching the head.

 

[Snaptrax]

Hmm if you are getting spark and fuel it should fire. Check the timing as well and also adjust your valves.
The valves should be adjusted to 0.003 of an inch on the exhuast and 0.004 on the inlet.
There is an awesome video on how to adjust valves but i cant seem to find it.

 

[my67xr]

to check your ignition coil,

set your multimeter to 200 Ohms
measure across the primary side of the ignition coil,
put one lead to the + terminal, other lead to the earth (mounting point)
it should read around .8 Ohms

then on the secondary side, set your meter to 20,000 Ohms,
put one lead to the + power terminal on the coil
and the other lead into the end of the coil lead (with the plug cap taken off)
it should read 3-5 ohms

 

[my67xr]

to test your stator output
find the stator wiring coming out of the l/h side cover and up to the loom, unplug it where it joins to the loom

set your Multimeter to 200 Ohms,
put one lead to the green wire, and the other lead to the blue w/white stripe wire it should read around 130 Ohms

now set it to 2000 Ohms,
put one lead the the green wire, and the other lead to the black w/red stripe wire, it should read around 380 Ohms


also these china bikes are reknown for having cheap terminals which can cause bad contacts, also the wiring is that thin, it can easily fracture or break
use some Dielectric grease on all the terminals to help stop corrosion and dirt from causing problems later.

CDI's, Coil Leads, Spark Plugs etc can fail too, use good quality ones when u can
if you have a china spark plug, chuck it and fit a decent NGK C7HSA, or an NGK Irridium CR7HIX


ps, Welcome to Miniriders too,
dont forget to drop by and say g'day in our Introduce Yourself thread too while you are here.

 

[Power93]

Wow, you guys are great! Thanks so much for the quick and informative replies!
I'll do a check on the components and let you know what I find.
What is involved in a valve tolerance check and do you need specific tools?
Oh and I replaced the china plug with an ngk.
Do you agree that being able to touch the plug as it fires isn't normal? Just thinking, it could be a loose earth as well. I'll have a look sarvo!
P.s don't know if I already mentioned it but I drained out all the old fuel and replaced it.
Thanks again

 

[zwebx]

"Do you agree that being able to touch the plug as it fires isn't normal? Just thinking, it could be a loose earth as" you should be getting a shock a pretty decent one too
make sure you have the plug earthing on the head or somthing like that..

To do the valve clearances you need a feeler gauge a 8mm and a adjustable spanner or a 9mm spanner.. i have done mine with a 9mm socket the last 5 times but that requires some skill..
as long as there a tiny bit loose at tdc of the crank *and bottom of the lobes on the cam* then there not a issue (and not excessive loose)

 

[zwebx]

some pliers would help too if there too tight, or you could buy the valve adjuster tool from dhz or somthing it takes the coordination out of it (need to hold the screw and tighten lock nut) you will see when your in there its very easy

 

[DustyFork]

Start with the wiring and if it has connectors check them for dirt or corrosion. Take off ya ignition cover and check pick up gap and it's all clean there. Check earth point aswell. If all fails maybe a cdi ignition box gone faulty but usually when they blow ya get no voltage in my experience. Sounds like you have a high resistance in ya wiring

 

[Power93]

Okay so here's what I've found. An earth wire that was completely disconnected at the lug.
The measurements I took were
Green to blue/white= 112 ohms
Green to red= 384 ohms
Green to coil+= 0.5 ohms
Coil+ to plug lead= 7.5 kila-ohms (extremely high!)
Green to motor (continuity test)= 0.1 ohms

All connections were pretty dirty.
Couldn't find the earth bolt but continuity was good anyway.
I'm thinking it's the lead??

 

[Power93]

Or it could be the coil, the lead and coil don't seem to detatch

 

[my67xr]

just take the end cap off the lead, unscrew this part that clips onto the spark plug
the cap alone is 5K Ohms