I recently bought a 2007 Hensim 400cc ATV and it ran excellent when I had first bought it. I took it out on a trail for the first time and it had died halfway through the trail and would not start back up again (luckily my buddy was with me and we had a tow rope). I got it back home to assess what was going on and I was able to get it started however it dies as soon as you give it any gas or dies a few seconds after it starts up. It has a weird quiet popping sound coming from under the gas tank near the carb and every so often the exhaust will backfire extremely loud. I had saw that it had some old gas in it. So I dumped all the fuel, cleaned the tank, changed the fuel filter / spark plug / and air cleaner, cleaned the carb really good along with all the jets, and made sure that the fuel tank/reservoir selector was clean and good to go, however it is still having the same issues. I had a buddy come check it out for me and he did a compression test for me and it was sitting at 130 which he said isn't bad. He then checked the timing for me and the timing was off by one tooth and he was able to adjust it for me but we were still getting the same issues. He then recommended to me that I change out the ignition coil and the CDI box. I have already ordered them and they are on there way from some other country so its going to be awhile. I was just curious if anyone else has seen this issue before and want to ensure that the CDI box and the ignition coil will fix it. Thanks.

 

First off, do you have a nice fat spark, if you do, it is extremely unlikely to be the coil, and fairly unlikely to be the CDI.

 

What else could it be then?

 

i would go back through the carb. Its really easy to miss some of those small holes in the jets

 

I went through it again for the third time and I am still getting the same issues. What would be the symptoms of a bad ignition coil or a bad CDI box?

 

Well I replaced the ignition coil today and it fixed it. Thanks for y'alls inputs.

 

Is the tank vent clear? I'd validate it's getting good fuel flow to the carb bowl by removing the bowl cover (leave fuel line attached) and turn fuel on...you should see a nice constant stream of fuel flowing (this is messy so use something to catch the fuel), but will give you confidence that the carb is getting the fuel it needs...


Because it's starting then dying...I'd focus on fuel delivery