Hensim intermittent spark
 

I'm currently working on a 2007 Hensim 400cc utility atv that does not run. I replaced the battery, new spark plug, rebuilt the carb as it had been parked since it quit running awile back, and tightened up a loose ground wire behind the coil. The quad turns over and fires occasionally but it has an intermittent spark. What should I check next?

I looked, and couldn't find anything on a 400cc hensim engine. I'm wondering if anything (like the ignition system) is similar to smaller engine quads. I have a 150cc GY6 Hensim quad. Does your CDI look like this?

Attachment 18949

If not, can you post a pic of your CDi and a link to where you got it?

It looks identical. Should there be 12v going to the CDI?

Maybe, but maybe not. There are two versions of this CDI which look identical, but are completely different inside and not compatible. Most CDIs that look this are powered of moderately high voltage AC coming from the stator. But there are a growing number that are powered off 12 volts from the ignition switch.

It is easy to tell the difference using a meter, and often is the first step when trying to fix ignition problems:

1) Unplug the CDI. Turn on the ignition, and set all kill switches to the "run" position. On the CDI connector in the wiring harness measure the *DC* voltage on the AC Ignition power pin to ground. If you get 12 volts DC then you have a DC powered CDI.

2) If you don't measure any voltage in 1) above then switch your meter over to AC volts on the 200 volt scale. Everything else is still the same (CDI unplugged, etc.). Crank the starter motor. Measure the AC ignition power pin voltage to ground while the engine is cranking. If you get 50 to 85 volts AC then your CDI is AC powered.

Both style CDIs run on moderately high voltage inside. The AC version just rectifies the high voltage AC from the stator. The DC version has a power supply inside that takes 12 volts DC and steps it up to a couple hundred volts to run the CDI. It is important to know which you have if you ever decide to order a new one. If you install the wrong one it won't work, and it is likely going to be destroyed.

Do you have a wire in your harness on the Kill switch pin?

If we establish that you have power (and which kind) to the CDI, and whether we need to consider kill switch input to the CDI, then we can go the right direction from here.

One of the difficult things is that you have intermittent spark. That means that you have to correlate all your results with whether or not your are getting spark at the time you are measuring, and only pay attention to the results while you're *not* getting spark. Measurements taken while you *are* get spark will only show that the quad is working - which isn't helpful.

I checked and it's a ac powered cdi. The atv does have a wire going to the kill switch pin

Am I right in assuming that you got an AC voltage of 50-85 volts AC while cranking the starter? This voltage is important imformation. What did you measure?

With the CDI unplugged, the kill switches set to the run position, and the ignition swith on, measure the resistance of the kill switch pin of the wiring harness to ground on the 100K ohm scale. What do you measure?

Set your meter to the lowest AC scale you have. Measure the AC voltage on the Ignition Timing Trigger pin while cranking the starter. What do you measure?

Set your meter to DC volts on the 200 volt scale. Hook the CDI back up. Measure the Ignition coil pin voltage to ground while cranking the engine. Watch it for 10 seconds. Describe what you see in detail even if it seems strange.

Once again, you have an intermittent spark. This makes it harder. You must only pay attention to the values you get while you aren't getting spark. Any measurements you get while the quad is working only shows that the quad is working.