I bought my grandson a used 50 cc atv, it ran when I bought it and he rode it 2 times. We went out to start it and it would not start. I had a friend look at it and he did some adjustments on the carb and got it running, When you opened the throttle full it would spit and bog but it still ran. He told me I might need to adjust then idle/air screw all the way in and back out 1 3/4 turns. I adjusted it in and it turned 4 1/2 turns till snug, then I adjusted it back out the 1 3/4 turns and now it will not start. I went back to the 4 1/2 turns and 1/3 turn in between and still no start. Any suggestions? I am hoping the screw with the spring around it was the screw I was suppose to turn. Pleasr help///

 

The screw with the spring is the idle screw the one you want to adjust if you are trying to adjust the air/fuel mixture is the one left to it almost all the way in the carb...

now does the quad start and die? what if you started it and kept on the throttle does it run? you want to back out that idle screw get it idling then you can play with the mixture following the thread on top this forum for adjusting the carb on chinese atv's

 

I figured out that I was adjusting the wrong screw. But now I cannot even get it to start. I checked to see if the plug was fouled out and I replaced it, as I was doing that I checked for spark and noticed that I could not see a spark, then I would see it arc once then no spark again, I adjusted the screw out as far as 6 1/2 turns, then started adjusting it in 1/4 turn at a time and still no start. I did then adjust the air/fuel mixture out to two turns and tried it, then 1 3/4 turns, still no start, I feathered the throttle to try to start and also tried to choke it and still nothing. Have no idea where to go from here. My friend who got it running for me the first time said he noticed the spark patteren too but he did get it to start. Is this normal spark procedure for this ATV. Help please.

 

You can do whatever to the fuel adjustment screws, but if you don't have spark you won't have a quad that will start.

Let's make sure your checking for spark correctly: Pull out the plug. Reconnect the spark plug wire. Turn on the ignition switch, apply the brakes, and set all kill switches to the run position. Hold the plug threads against the engine block. Crank the engine. You should see a steady stream of sparks occuring at about 10 times per second.

Do you see that?

If not then...

How many pins on your CDI? 4? 5? 6 (2 pin and four pin)? Do you have one of those left handlebar kill switches that require you to set it back to the center position and then *push it in* until it goes *click*?

 

Yes I did try that. I was getting no spark then I would see 1 arc and then nothing. what do you mean by pins on my cdi. How do I tell. No I do not have a kill switch or fuel shut off valve. Just a push button on off switch on the left handlebar side is all there is. It was running and starting fine( started hard when it sat over nite sometimes) until I moved that idle screw in,??????

 

Look at the following:







See anything that looks like your quad CDI?

I'm particularly interested in the "1 arc" thing. Is this repeatable? Please describe this in as much detail as possible. Don't hold back. Let it all out...

I also need to know what CDI you have based on the above. If you have the six pin CDI we may need to go through another gauntlet of questions to see if it is DC aor AC powered...

 

It looks like the middle one. I have not taken it off but there are 4 wires going into it. As far as the spark, watching it I will see no spark, then I will see 1 arc, then nothing again, It is very intermitten when it does it. My friend who fixed it said he noticed there was no spark either but he got it running and when I picked it up it ran for 3 days, I adjusted the throttle screw in so it would not go fast as this is for my 4 year old grandson, it started to bog when he would get going full throttle, thats when i thought the air/fuel mixture was not correct. When I adjusted the idle air screw on accident,then it wouldnt start at all.

 

I've never seen a five pin CDI with only four wires going to it. Are you sure it is a five pin (middle picture) and not a four pin (first picture)?

The difference between the two CDIs is important. The four pin CDI is powered off 12 volts DC, and the 5 pin CDI is powered off moderately high voltage AC (a couple hundred volts). The troubleshooting procedure is different for the two CDIs, so we need to nail this one down accurately.

If you do have a five pin CDI, which of the 5 wires is missing? Ground, AC Power, Trigger, Ignition Coil, and Kill are the choices. I think you can see that all five of these are necessary...

What are the colors of the wires going to your CDI?

On the intermittent single spark: Does this single spark happen only at the start of cranking (when you first push the start button), only at the end of cranking (when you release the start button), or does it happen at totally random times (including the in middle of cranking the starter over several seconds)?

 

lynn, im just stabbing in the dark here but if its the 12v dc cdi then would the strength of the battery have anything to do with it not sparking? although i suppose it wouldnt be turning over great if it was.. because if it did then hooking a car battery to it in parallel it might sort it out...
but as i said im just stabbing in the dark

 

Since it is really hard to know what someone elses design does with presented with a low input voltage it is hard to say. It is a possibility at least, and jumping the quad battery to a car battery is easy to do. So it is a worthwhile test...

The one spark issue (if it happens only when the starter is being first engaged, or only when the starter motor is disengaged) sort of points toward problems with the timing trigger signal - but only if it happens at the beginning or end of engaging the starter.