Experts,

I need some guidance here. Bought a group of Chinese quads, and have been able to get all of them running and mobile but this one. It claims to be a SUNL 100cc.

Starter is turning the engine, and its producing a nice strong spark, but I can't get ANY life out of the engine.

I can feel a nice push of air from the piston with the sparkplug removed, but this doesn't really mean I have good compression.

Even if I remove the carb from the mix and shoot high-performance starter fluid directly into the cylinder I don't get nothing, no pop, no short run...nothing.

Now from my days of small lawn mower repair, this typically would mean one of two things:

1. Timing is off for some reason
or
2. No compression

I'm sorta hoping you guys might be able to help me with potential alternative issues that I may have missed being that I'm not familiar fully with the ATV engines.

Thanks in advance

Lord Vokk

 

Is your quad a four stroke? If so have you tried adjusting the valves?

Compression is best measured with a compression tester, but many have use the "thumb over the spark plug hole" method. Put your thumb over the spark plug hole and seal it as best you can. Crank the engine. Can you hold back the pressure or does it force your thumb off (and make a loud "pop" at the same time)?

 

Lynn,

Thanks for the reply! I'll be checking the compression and the valves over the next couple of days. I'll report back the findings.

LV

 

Lynn,

Again thanks for your help. Just to follow-up. Compression is fine and valves are adjusted. Timing is also great, right on the money. However, no change in overall status.

This one truely has me baffled....I have spark, fuel and compression, but no starting.

Can you explain to me what powers the 'spark' while starting, is it the battery or the stator?

Also, what controls the 'charging' of the battery, is this a function of the voltage regulator? In an old Chevy the voltage regulator is what determines if you are using battery power or switched to using the power generated by the alternator. Does the voltage regulator fulfill that same duty on an ATV?

Thanks in advance,

LV

 

So you have spark, fuel, and compression. And the timing is correct. Then it should start.

Out of curiousity, how did you check the timing? What did you set the valve clearance to?

The spark is powered off either the 12 volt power bus, or off moderately high voltage AC from the stator. The AC from the stator is more common on older quads. Newer quads are now sometimes using 12 volts. How many pins on your CDI? If it is 6 pins (2 pins and 4 pins on two connectors) then it could be either 12 volts or AC. If it is a 5 pin CDI it is AC powered.

But the ignition system is much more involved than just having a power source. You need a trigger pulse from the stator (at the right time), a properly functioning CDI, and working ignition coil, and a good spark plug.

The battery charging system is somewhat similar to the alternator on a car. On a quad the stator generates low voltage AC by spinning magnets in the flywheel past coils of wire. The voltage is rectified into DC and regulated to 14 volts (+/- 0.5 volts) by the voltage regulator and applied to the battery. This keeps the battery charged.

There is no active switching between battery power and stator power. They are both simply wired up together. If the stator (and voltage regulator) can muster it, it raises the battery voltage up to 14 volts. This is higher than the 12.6 volts from the battery, and causes current to flow backwards through the battery which charges it up. If the stator and voltage regulator cannot muster enough power to raise up the battery voltage then some of the power to run the quad 12 volt bus comes from the stator, and the rest comes from the battery. As long as the charging system charges more than it discharges the battery will be OK.

 

Your post is aways full of good info, yet always opens a new can of worms :-)

The valve setting are as follows... .003 for the intake and .005 for the exhaust.

Now for this statement..."Timing is also great, right on the money". This was a poor choice of words, it probably should have read, "Timing chain looked good and the cam is in the correct relative position to the crankshaft".

This timing thing is actually where I'm focusing my energy currently. I've read in a couple of places that the stator could produce a strong spark, yet not accurately send the "pulses" to the CDI, leading to a delayed or inconsistent spark.

It seems this condition could be caused by a number of things, bad wire, bad connection, bad stator. My next series of tests are going to be focused on validing that the "pulses" are (or are not) getting to the CDI.

I'll keep this thread updated. The weather here in NC has slowed my abililty to work in the shop, so it might be a few days before the next update.

Thanks again,

LV

 

Lynn,

My hunch was correct, I had a little bit of time today and did some testing.

I'm like 95% sure that my problem is the "pulse trigger". It doesn't appear to be generating enough voltage to trigger the CDI.

I've semi-validated this by doing the same battery of tests on a similar ATV and comparing the results.

If the "pulse trigger" isn't working what are the likely causes? Does this automatically mean I new stator is needed or is there potentially a 'fix' to correct the situation?

Thanks again,

LV

 

I don't think this where your problem is. If you don't get a trigger signal from the stator then you don't get spark. Or to look at from a different angle, if you are getting spark then you are almost certainly getting a trigger pulse. There is no in between. You either trigger the CDI and get a spark, or you don't trigger the CDI and don't get a spark.

This is also worth noting: The trigger pulse amplitude from the stator is directly proportional to engine speed, so if you have a marginal condition where the trigger signal amplitude is right on the edge of triggering or not triggering the CDI, then anything that makes the starter crank faster will raise the trigger voltage (and bring it out of the marginal region). One way to do this is to jump the quad to your *running* car. The car alternator will raise the battery voltage at the quad to 14 volts (instead of 12.6 volts), and make the quad crank a little faster. But realize that this would be for intermittent spark, not strong spark but no starting. This is not your problem.

Above I said that "if you are getting spark then you are almost certainly getting a trigger pulse". The reason for the phrase "almost certainly" instead of "certainly" is that a defective CDI can sometimes trigger itself whether or not there is any trigger signal from the stator. When this happens the erroneous "trigger" will be at the wrong time and so you will have spark - but the engine won't run. This is a rare failure, but it does happen. On most quad you can test this: Look for an access plug in the engine cover above the flywheel that you can remove. [On quads that have these many new owners mistakenly add oil into this hole.] Shine a timing light down this hole and see if the ignition timing is correct. You will be able to see timing marks on the flywheel with the strobe light to check timing. But if this is your problem, then the CDI is the bad part - not the stator.

 

Lynn,

Let me take a minute to level set.

You were correct, the "pulse trigger" was 'working' <----air quotes

It was sending a pulse at a reduced voltage...somewhere around 1.4 volts. This was making the CDI spark, I could prove this by simply cutting the pulse wire. Cutting this wire caused the spark to cease.

Here was the kicker, the lower voltage pointed to a problem with the pulse and the problem was keeping the CDI from keeping good time.

---------

Believing this was still the issue, today, I pulled the cover/stator and I found that the cover actually had two cutouts forward of the front sprocket. These cutouts are part of the original factory casting.

So effectively, everytime you ride one of these ATVs, if the chain is getting wet or getting mud on it, that water/mud is slung all around under the cover that hides the front sprocket from view. Which also means that it's also being slung into these two cutouts.

So water and mud is able to basically get into the housing that covers the flywheel and the stator.

Effectively, the low voltage issue was due to the fact that the pulse coil was basically half covered in dried mud that entered the system per the process above.

I pulled the stator and the shroud. I cleaned them all up and reinstalled. Tried starting the ATV and it fired right up.

The ATV still needs some tuning work, but it now starts with little issue.

--------

Lynn, I want to thank you for all your help. Simply, having someone to converse with helped me keep some of my hair.

I hope this thread will serve to help others that may face a similar situation in the future.

Thanks again,

LV

 

I am also haveing the same problem, I bought a loncin 70cc 22E atv for my nephew. I have great spark blue and i used the old timers way my uncle recomended, sticking a screw driver in the plug cap, and it lit me up good!! timed it, checked compression did everything i can think of and ive worked on alot of atv'c over the years, at first it wouldnt kick over to save its life until i timed it and now it will kick and kick and sometimes start but cant keep it going, and i actualy dont have a battery in it i'm useing a boost on my battery charger to start it and it turns over great is there anything u can think of that i can do. thank u.