I finally broke down and got into ATVing. To see if I would like it I shopped around for a used one. It is a '91 Big Bear 350 4x4. Not the fastest thing in the world but strong as an OX. The previous owner maintained it very well. I have a couple of questions regarding this machine.

1) Idle: When it is first started, it idles really bad until it warms up. It even stalls sometimes. After that it runs fine. Is this normal or something wrong?

2) Heat: When running slowly in the summer the machine gets so hot that you that you think your legs will burn up. Any advice for cooling this down. One person posted a solution of using Synthetic 5W50. Any Opinions or options ?

3) Brakes: The front brakes require pumping to get them to work. Normal ?

4) Front diff.: I recently took it out into the snow. I noticed that if I lost traction on the rear wheels only one of the front wheels spins. I thought they moved together. My friend has a '95 HONDA TRX300 4x4. All his wheels move together.
Any comments? Is it right ?

Thanks

P.S. Great site.

 

i hope i can help you it sounds like nothing out of the ordinary to me first i have been riding yamahas for ten years and all of my buddies ride them also with the exception of 2 and every one i've been around is acold blooded machine and takes a few minutes to reach temperature to smooth out on the idle. Secondly the big bear is a air cooled motor and during slow putts through the woods and leisurely riding will heat up the motor due to not enough air being moved around the motor which happens at higher speeds. Thirdly pumping the brakes is a real good indication there is air in your line remove the cap on your master cylinder and check fluid and locate bleed screw and pump until no air bubbles are present this should solve your problem. And lastly your machine is equipped with a limited slip differential and both wheels will not spin in loose ground only the wheel that is sensing the most slippage i hope this helps.

 

I agree with Jed totally on all his answers.The front brakes may have air in them but the shoes are probably worn out. I would pull a brake drum off and check the thickness of the shoes. Bleeding them might help but if your shoes are worn out they will have to be replaced I had a Big Bear and I know that the front shoes dont last very long.

 

1. Check to see if you have a manual choke on the side of your carburetor. My '96 BB does and will idle relatively smooth in the colder weather with the choke pulled out to the first notch when it's first started. In the warmer weather, no choke is necessary. But, in any weather condition, you may find your ATV idling a little rough until it reaches a normal operating temperature.

2. My '96 gets warm too, but the over-heated light doesn't come on. Oil can make a slight difference but as Jed already mentioned, it's an air-cooled ATV and will tend to run hot at idle or slow riding speeds. If you're sitting around on a hot day waiting for riding buddies to catch up to you on the trail (or just admiring the view), 5 to 10 minutes of shut down time will allow your engine to cool down enough to make a difference.

3. Sounds like you need to bleed your brakes. Also, your brake shoes may need replacing if they're worn too far (can also cause you to have to pump the brakes to apply them sufficiently). It's been posted before to use aftermarket brake shoes that have grooves cut in them to improve braking performance.

4. Agree with Jed. You do NOT have a posi front end. Very few makes/models come with a true locking front differential. However, there are aftermarket designs to convert to a locking differential but they too have their drawbacks such as a gain in turning radius.

Good luck!

 

OK....they are right about all the questions....but my bigbear never does get hot..mine is a 97 and it has an oilcooler on it but im not sure if 91 model does...if it does the fins could be bent or it could be clogged with mud

one other thing....to all BIGBEAR owners with the 350cc engine....my bigbear is in the shop now with a broke crankcase....the dealer said this is a VERY COMMON problem with these machines and there is nothing they can do about it except replace it....but i found out today that it is going to be fixed for FREE since this is so common so take yours in and have it looked at..im not sure what year models have this problem but it sure is a pain since it will be in the shop for 4 weeks

 

BB4x4: How did the crankcase break? From the outside in? (i.e. rock smashing the case) From the inside out? (i.e. throwing a connecting rod)

Is it just fractured? Or is there actually a hole? What were you doing with the ATV at the time this happened?

FYI, I believe most BBs come with external oil coolers. Like you, not sure if the '91 does (assuming it does). Mine only gets hot on a warmer day AND if I was riding the trail hard and fast - whether or not the oil cooler is clean or caked with mud & debris.

 

Broken crankcase is a common promplem!WOW what a promplem!

 

Thanks for all the feedback. The crankcase bit really has me scared.

I too would like to know what caused the crankcase blowout.... We will know what NOT to do.

F.Y.I. the '91 does have an external oil cooler. During normal riding the quad is OK. When driven slow in summer you can really feel the heat.

But... The oil light never goes on. The oil has come on for an instant when driven under the following situation.

1) Driven for awhile.
2) Turn off the quad for a few minutes.
3) Restart to continue.

I don't think it is bad since the light goes out right away. I do get the impression that the oil is being pushed pretty much at it's limit.

 

If oil will help use a hight tec. oil like mobile 1 snythtic and change more often than recomended.