Yamaha Grizzly ATV Forum banner
1 - 13 of 13 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter · #1 ·
Hi,

I am working on a friend's '01 Big Bear 400 4x4. When I first got it, the battery was dead so I was pull starting it. It would run for a while, with an erratic idle, then die with a pop. I'm not too good with carbs, so instead of rebuilding I just put a Centric carb in it. And a battery. It fired up, ran a little rough, then stalled. It wouldn't start for a few minutes then when it did start, it did the same thing. When I pressed the start button it didn't crank, but the oil/temp light would come on. After sitting for a few minutes it would crank. It's full of oil so I'm thinking it's overheating but not sure why. I'm new to quads, and don't have a manual or anything for it so I could use some help. Thanks!

-Tim
 

·
Registered
Joined
·
541 Posts
Hi Tim, It is not overheating. Sounds more like you have a fuel problem. Not sure about that carb, was it new? Other things to check - fuel line for good flow, fuel strainer for clogs, gas cap vent for flow.

When you say full of oil, how full? You are checking with the dipstick, right?
 
  • Like
Reactions: Timbro

·
Registered
Joined
·
4 Posts
Discussion Starter · #3 · (Edited)
Hi Greg, thanks for replying. Yeah, it was a new carb. I put a little fuel filter inline, and it's getting fuel. Didn't know there was a fuel strainer, do you know where it is? The vent cap is not plugged, I can easily blow air through the vent hole. Dipstick says it has oil in it, at the correct level. If it's just a fuel problem why won't the starter crank when I press the button after it stalls? And when I press the button and it doesn't crank, the oil/temp light comes on and stays on until I let off the start button.
 

·
Registered
Joined
·
541 Posts
The fuel strainer is attached to the fuel petcock inside the tank. It is simply a fine mesh screen which may be plugged up with crap, but if you can see fuel flowing then that is probably not the issue.

Looks like you also have some strange electrical issues too. I don't want to jump directly to the cdi unit being bad, but someone else on the forum had similar electircal issues and it turned out their cdi unit was bad. If you have air, fuel and a spark then it will run, and the only issue here seems to be spark/electrical. Since it runs sometimes, and you get strange things happening after it dies, I'm leaning towards the cdi.

Maybe someone else knows something else to check here.
 
  • Like
Reactions: Timbro

·
Registered
Joined
·
4 Posts
Discussion Starter · #5 ·
Hey Greg,

I feel kinda dumb, but I just pulled the tank to clean out the petcock, and found what I think was water in the gas (I thought I had gotten all of the old gas out). So after putting in the new carb yesterday, I ran it with watery gas for about 5 minutes. Today I cleaned out the tank, put some new gas in, and it ran, but it's still having problems. It idles too high, then idles down to normail-ish, then back up too high and keeps doing that. But if I give it any throttle it backfires and sputters, or backfires and stalls if I give it more. It's definitely getting good gas flow, and finally clean gas. I didn't have any problems starting it after it stalled this time. I read somewhere these carbs sometimes don't come adjusted right, and you have to drill out a cap to get to the adjusting screw. I'm thinking too rich, but like I said earlier I'm not experienced with carbs. I really appreciate your advice. Does it sound like it's just running too rich, or could the cdi be causing the varying idle? Thanks again!!
 

·
Registered
Joined
·
175 Posts
Sounds like you might have a vacuum leak to me.

Too fast an idle speed.
If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft.

A rough idle or stalling.
A performance cam with lots of valve overlap can give an engine a lopping idle, but so can a vacuum leak. A really serious leak can lean the air/fuel mixture out to such an extent that an engine won't idle at all. An EGR valve that is stuck open at idle can have the same effect as a vacuum leak. So too can the wrong PCV valve (one that flows too much air for the application), or a loose PCV hose. The rough idle in these cases is caused by "lean misfire." The fuel mixture is too lean to ignite reliably so it often misfires and fails to ignite at all. Lean misfire will show up as elevated hydrocarbon (HC) readings in the exhaust, enough, in fact, to cause a vehicle to fail an emissions test.

Hesitation or misfiring when accelerating.
This may be due to a vacuum leak, but it can also be caused by a weak or inoperative accelerator pump in a carburetor, dirty injectors, or even ignition problems such as a cracked coil, worn spark plugs or incorrectly gapped plugs.
An idle mixture that defies adjustment. When setting the idle mixture adjustment screws on a carburetor, the idle speed should start to falter as the adjustment screws are turned in to lean out the mixture. If the screws seem to have little or no effect on idle, you have either got a carburetor problem or a vacuum leak.

The important thing to keep in mind about vacuum leaks is that they have the most noticeable effect at idle. At part and full throttle, there is so much air entering the engine that a little extra air from a vacuum leak has a negligible effect.
 
  • Like
Reactions: Timbro

·
Registered
Joined
·
1 Posts
I have an 01 big bear 400 4x4 was running great for awhile I put a new petcock in the fuel tank all new fuel filter and fuel line new carburetor new air cleaner new coil and new spark plug and it started acting up it will run good for like 5or ten minutes then starts sputtering out and will die when I give it throttle but if I open the choke it starts running a little bit so if you have and answers to what the problem is I would like to know
 

·
Registered
Joined
·
351 Posts
I worked on a Bruin 350 that would idle ok but when given throttle it would sputter and die. Checked gas tank looked good but drained anyway and filled with fresh gas. If the choke was on it would run with throttle. It was a fuel/carb issue. I wasn't in the position for a carb rebuild so I pulled the fuel line, ran engine until carb empty, and then filled carb with WD40 while cranking engine. Let sit full of WD40 for a couple of beers. Hooked up fuel line and it ran great. That was 2 years ago and they say it's still running good.
 

·
Registered
Joined
·
1 Posts
Great info overall from all participants, I have recently started working on a friends of mine, 2001 big bear, he had starting issues and after taking a quick look at it I found that draining the tank and throwing a carb kit in it was his best bet, it did not idle originally, after replacing these parts, cleaning the plug and draining the tank, it will run, it will idle, it will accelerate until mid throttle then it start sputtering and backfiring, I have not checked the valves or timing, before I do so are there any other issues that I should check first?
 

·
Registered
Joined
·
1 Posts
Will the vent cap on a 00 big bear 400 cause air bubbles in the gas line going to carb . And also my vent cap is pushing up gas bubbles through it.
 

·
Premium Member
Joined
·
12,491 Posts
You last two posters should start new threads for us to help more.....heat on the bottom of the tank can cause boiling gas.
 

·
Registered
Joined
·
1 Posts
Hey just joined because I was looking at issues and fixes yall were having. I'm working on a 96? 97? Yamaha big bear and guy from work brought it to me to get it running after 4 years and some general maintenance and I noticed it was acting cold blooded. Fixed what he asked , gave it back, now he wants the cold starting issue fixed. Took the tank off, checked to see if it was maybe valve lash? It would start up cold just fine but die a minute later , same issues, idle would climb then lower. Took the carb off because I was thinking of cleaning it again, low and behold - the rubber intake manifold had a Crack in it, chased it down and the aluminum inside of it oxidized and broke the rubber free from it and was leaking air 65% of the circumference of the intake . Don't know if that helps anyone but there you go.
 
1 - 13 of 13 Posts
Top