Yamaha Big Bear 400

Hi!

New member here and I've got lots of questions. A little background: a
friend of mine has a farm in NH. He uses his Big Bear to work in the
fields, etc, etc. Recently it has stopped running, and in exchange for
getting it running again, I get a toy for the winter. Today I got it
running; all it took was a charged battery, free an apparently stuck float
and some clean gas. I'd like to get it running the best I can for him so
that's why I'm here. First off, neither he nor I know what year ATV it is.
I poked around on the motor for a while looking for a vin plate with some
year information, but to no avail. I'm quite mechanically inclined, so I'm
looking forward to the work, however I'm not an ATV guy so I'm going in
pretty blind. Here's the list of questions that I have:

1. Where would I look to find the model year? Is it stamped/plated to the
motor someplace?
2. I assume 4 quarts (or close anyway) of oil. Any reason to go full
synthetic over a synthetic blend? Not knowing how many miles are on it, I
don't even know whether it's ready for a synth-based oil.
3. I found the air cleaner under the seat. Worth chaning to any
aftermarket-type filter? Without changing the exhaust or fuel levels,
would it really help out any?
4. I'm not sure whether the plug that's currently in it is correct. Does
anyone know what gap and heat I should be using?
5. Are ATV service manuals available for download anywhere? I know that
all my questions will be answered in there!

Thanks for all your help with this. Look forward to being part of the
forum!

Mike

Should be more like 2 quarts and regular oil should be just fine for it.
Wouldn't hurt to get a foam filter for it.
Best thing to do, would be to talk to a dealer, see if they could steer you in the right direction on finding out the year of the machine. They might even have a manual for it in stock.

Look at the front left framerail coming from the top of the frame.It should be somewhere in there or even possibly on the crossbar between the 2 front framerails.

It should take around 2 1/2 to 3 quarts of oil.There is no really advantage to running full synthetic if the motor isnt built for performance,you wont really get anything out if unless it is very hot where you live.



If it is realy dusty there then I would keep the foam filter,it does alot better job keeping the small dust particels out.I would look into a Twin Air filter or something along those lines.Also remember you have to keep foam filter oil on it or it will let dust in the motor.Dont use regular motor oil as it will drip off and the filter will be dry then.


Without knowing the year I really cant tell what plug to use but the heat range should be about an 8.


Dont know of any manuals you can download from the internet but after you find out what year it is you can go to ATV Parts,Snowmobile,Motorcycles Parts ATV,Snowmobile & Motorcycle Accessories and look up all the info you need.


Hope this helps some and welcome to the site..

Once you know the year, you can view your manual here:
My Yamaha Prompt - Owners Manual




By the way, to the site and glad you found us

If you have any picutres of your Big Bear 400, please post'em in the gallery. We'd love to see them

Enjoy the ride!

the vin # is behind the front left mudflap on the lower framerail, the best thing i did for mine was to go up one size on the mainjet in the carb