I don't think it is the carb (not ruling it out though). I have had the carb off 3 times this weekend. I had put a dyno-jet kit on a few years ago and I went back to the original main jet and needle to try to eliminate as much as possible.

I am going to try the spark plug tomorrow. I wanted to measure it when running correctly and when messing up but I was afraid that the voltage would be too much for my voltmeter.

 

Check battery voltage when it is running good and when it acts up, at idle and supposely at 5000rpm. At the high rpm it should be from 14 to 15.5 volts. Their has been several on here that acts up like yours and it ended up being a bad voltage regulator going to high, like 18volts freaking out the cdi unit.

 

New development with my quad, I think the coil finally went. After it quit on me yesterday, I left it in the building. I bought two new plugs this morning and went out to run it and try measuring the battery voltage and check the spark when it was messing up. Never got to check it. It would not start. Grounded the plug to the case, hit the starter and NOTHING!!

Thinking about ordering a coil in the morning. Hoping that is the problem.

 

deerslayer if you have a good Dealership like mine if you remove the old coil and take it to the dealer they will check it out free of charge , i've taken electrical part's to my dealer that were a different brand [ even before i bought my 2006 AC 400 FIS Auto 4x4 from her ] ; and she would do this for anyone even if they didn't buy from her !

I know not all Dealership's are as good as mine and some will ask you to bring the quad to the shop , [ telling the owner's that they can't test electrical part's unless they're on the quad ] But that is when you can tell if you have an honest dealer ; my dealer told me she could check these part's without having them on the quad !

Good luck with your quad !

williebee........

 

Sounds like you got it.

 

Has anybody measured the resistance on the ignition coil. I have mine off the bike and it is measuring about 6.5 k ohms from the spark plug output to either of the "inputs". The inputs are showing that they are shorted.

Does this seem correct?

 

my service manual says the following for AC 400/500

Ignition coil Resistance
- (Primary) 0.4-0.6 ohm terminal to ground
- (Secondary) 5200-7800 ohms high tension plug cap removed to ground

Also, I had an old Suzuki atv that did something similar to yours.It would start and run for a spell then just die. You could crank it until the battery was dead and it would not run. Let it sit and it would start back up. I discovered by accident that if I kept my CDI cooled it would run for as long as I needed it.

I replaced the CDI and my problem went away. I am not suggesting you blindly "replace" the CDI though as it is VERY spendy. However, if you rule out the coil you might look into that as well.

Swampy

 

Looks like I am going to have to buy a service manual. From looking at the one online that Fossil referenced, it has a ton of invaluable info for troubleshooting. Wish I had found that sooner.

Anyways, the online manual does not have the wiring diagram. It is missing from the last pages. Does anybody have one for a 2003 400 4x4 auto. The manual says that the voltage on the blue/white wire should be 31 VDC with the switch on and 130 VDC with the starter engaged. Mine is reading around 300 VDC before hitting the starter and I don't see much change after hitting the starter. need to trace that wire to see what it is coming from. The parts diagram on arcticcatpartshouse.com looks like it might be coming straight from the CDI.... I surely hope that isn't bad!!!

 

deerslayer01,

There is a file on the same website which has all the wiring diagrams for AC ATV's and Snow machines for 2000 - 2009

Link is "K&T Parts House Lawn Mower Parts and Chain Saw & Trimmer Parts"

6th one down in the list

Large file 450 mb

 

Thanks fossil. I found a white/blue in the harness at the cdi. checked it with my meter and it is the same wire that goes to the coil. Now I need to figure out if something on the input side of the cdi is causing this high voltage or if the problem is the cdi.