Hi,

My son has some noname 110cc china ATV. He had been riding it, and it ran great (better than my 150cc ). The next day it wouldn't start. The starter turns/cranks the engine just fine.

So I tried 2 different plugs, but nothing.
Tried another working ignition coil, still nothing
Then I tore apart the carb (3 times so far) to clean it out, still no result. When opening the drain screw on the carb, gas is comming out.
I then tried with 2 brand new CDI's, same result, not starting.
I know all replaced parts are working, because they work fine on another quad.
Removed kill switch from CDI, just to rule that out, still not starting.

I have a spark, if I ground the plug to cylinder head.

I have done a CDI readout which I've seen in another post.

Ohm Should be
Trigger timer to ground 150 Ohm Reading: 124
Ignition Coil to ground 0.5 Ohm Reading: 6
Kill Switch to ground Infinite Reading: 460000
AC Ignition Power to ground 400 Ohm Reading: 599


Volt while cranking Should be
Trigger timer to ground 0.2-0.4 Vac Reading: 0.38
Ignition Coil to ground
Kill Switch to ground
AC Ignition Power to ground 40-80 Vac Reading: 73

I can see that the ignition Coil to ground is a little high, but is that enough to stop it from starting?

Any help would be appreciated

 

Forget about the electrical stuff. If you have spark, it's working. Have the valves (lash) ever been checked?

 

No, I haven't checked the valves while the quad has been here, aprox 6 months.

But that was also going to be my next move, and then the timing if that doesn't workout either.

 

So, I've been working with the quad 6 hours today, but it still won't start.

Turned out that the plug was periodicly faulty, the wiring connector to the cdi was also in bad shape, hence seeing spark when plug was out, but not in. Valves has also been checked for the right clearance. (Damn it was hard to find TDC. 3 marks on the flywheel)

I managed to get the engine to run today, but only 20 sec at the time, then it stalls, and I have to wait like 5-10 minutes before it will start again. When it runs, black smoke is coming from the exhaust (like a mist), and it smells kinda burnt.

Right now I'm thinking a carb issue, but I don't know. Any help would be appreciated. Thanks.

 

Yup, i think your on the right path. R&R that carb. Pay attention to those jets and float plunger. Clean it out real good. Pilot jet has very very small holes and must be clear.

 

I'd look into just replacing the carb. Mine had a carb issue, I took it apart and cleaned it, still couldn't get it running, put the new one in and it started right up. I bought a new one off loncinengineparts.com for $10.

 

So, today I've rebuild the carb with all new parts, jets, screws and everything, but no, won't start.

Tried a brand new carb, still nothing.

Tomorrow I'll try to pull the top off and check the valves, maybe one of them has become bend/smashed.

I'm starting to lose my hair!

 

The top has now been removed, and the piston and the valves looks fine. Black but not bend or smashed. Piston rings seems a little sluggish tho, so gonna order some new ones.

Still haven't found an obvious cause why the quad won't start.

 

Where are you located? Maybe someone local to you can assist? Did you pull compression before you disassembled the top end?

 

Check the compression too. I had a similar problem with a Coolster 125cc and did all the usual carb, ignition and valve clearance drills.
Turns out the head gasket was blown at the timing chain passage and was leaking compression internally to the crankcase.
Easy, $5.00 fix after sending time and money swapping parts.