I have a 2002 400ex. Ever since I got it (brand new) I have had trouble starting it. If I put a new spark plug in it will start up, but after riding the plug will be totally black and will not start again. I brought it back to the dealer and they say there is nothing wrong with it and it could be from stale gas. The dealer told me that u have to put stabalizer in the gas even if u ride every weekend. Is this true? Can anyone help me out with might cause the plug to carb up all the time? Also, the atv is totally stock, what octane gas should i use? thanks for your help

 

the jetting is most likely your problem, you could try leaning out the main and/or the needle jet. i am not sure what the manufacturer recomends for octaine but i have always put in 89 or 91 octaine. putting stabilizer in your gas if it will only be sitting a week is bull crap, i wouldnt ask that dealer for any advice on anything else if i were u.

 

when starting the bike don't keep hitting the throttle. just pump it a couple times at most then hit the start button without hitting the gas any more. if you do, you will flood it and your plug will be really black. also, make sure your not driving it with the choke on. this would richen up the air/fuel ratio causing a black plug too.

 

You cant flood the bike by pumping the throttle. It works on vaccum in order to get gas to the cylinder. If its not running the theres no vaccum. Try to lean out the main, I think thats your best bet.

 

What about the accelerator pump. Are you saying it works on vacuum. I thought it was manual.

 

Go to your bike and see. It will not flood. I gaurantee it. Maybe some of the new bikes like the predator may cause I think it has a fuel pump on it.

 

The accelerator pump is manual, it shoots gas into the intake port when you pump the gas, the polaris predator uses a vaccum setup. Just pump the gas a few times before you start it and it will start every time.

 

Does the motor use any oil?
Is the air filter dirty and plugged?Is it oiled with air filter oil?
does it have any drivability problems, hesitation, backfire, missing, bogging?
If it doesnt have any drivability problems A simple solution would be to go one heat range hotter on the spark plug.
Gas should stay fresh for 2 months, if you use it up, before 2 months, you dont need stabilizer.

 

no, it doesnt have problems while its running. the only other thing it does, is after not being able to start it, and then changing the plug, once it starts up it will blow black smoke out of the exhaust in the beginning and then be fine

thanks for your help

 

You are absolutly right about the pump. I changed my jets today and I noticed everything, I was thinking "man I was wrong". But anyway Sorry. Im just used to my old 350x.