Help! Big Bear with no power - ATV Forum - All Terrain Vehicle discussion for Honda, Yamaha and more ATVs
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post #1 of 33 (permalink) Old 05-14-2011, 09:11 PM Thread Starter
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Help! Big Bear with no power

Ok, so last month I noticed my 96 Yamaha big bear 350 SE was lacking power. I took off the clutch cover and found the centrifugal clutch was very worn. I replaced the clutch with a 2ed hand one that was in good shape and has lots of material left on it. I also replaced the clutch packs as I figured I might as well for the extra $40 seeing as how I had it apart. Changed the oil. Have 10w40 atv oil in it now.

So I took it out today and still no power. It starts and idles fine but in higher gears it will bog down and if I try to spin the wheels by pushing against a telephone pole, ect it will just start to push and then bog down. It won't spin the tires at all under load.

-I've cleaned the carb a million times.
-No holes in any intake boots ect.
-Air filter is clean.
-I've adjusted the clutch from one extreem to the other with that little screw on the side with no change at all
-I've played with the air/fuel screw on the carb with no change at all
-I haven't really checked compression but it will blow my thumb right off the hole when cranking

It just started doing this suddenly and I'm running out of ideas on what it could be. Any thoughts?
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post #2 of 33 (permalink) Old 05-15-2011, 07:36 PM
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Lack of power 350 SE

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Originally Posted by Ljungman View Post
Ok, so last month I noticed my 96 Yamaha big bear 350 SE was lacking power. I took off the clutch cover and found the centrifugal clutch was very worn. I replaced the clutch with a 2ed hand one that was in good shape and has lots of material left on it. I also replaced the clutch packs as I figured I might as well for the extra $40 seeing as how I had it apart. Changed the oil. Have 10w40 atv oil in it now.

So I took it out today and still no power. It starts and idles fine but in higher gears it will bog down and if I try to spin the wheels by pushing against a telephone pole, ect it will just start to push and then bog down. It won't spin the tires at all under load.

-I've cleaned the carb a million times.
-No holes in any intake boots ect.
-Air filter is clean.
-I've adjusted the clutch from one extreem to the other with that little screw on the side with no change at all
-I've played with the air/fuel screw on the carb with no change at all
-I haven't really checked compression but it will blow my thumb right off the hole when cranking

It just started doing this suddenly and I'm running out of ideas on what it could be. Any thoughts?
A couple of questions. Does it seem like it is hitting top rev's or does it seem to strain and not get high rpm? Or does it hit high rpm and just not go fast? Is there any strange sound or vibration, any strange smell, like something hot or a smell of engine oil?
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post #3 of 33 (permalink) Old 05-15-2011, 08:22 PM Thread Starter
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It just struggles to pick up speed in 4th and 5th. It will be going along, and then fall back, the pick up a bit of speed again. And like I said, I can't spin the tires when against a phone pole. It just bogs out. It's excatly like I'm in too high a gear. Like if I'm tring to push on the pole in 3rd or 4th.

Actually, I took out that 2ed hanmd clutch today and it really isn't any thicker than my old one....I may have to get a brand new one, but I'd like to know that it's the problem before I do.

Last edited by Ljungman; 05-15-2011 at 08:39 PM.
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post #4 of 33 (permalink) Old 05-15-2011, 09:40 PM
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No Power

A 96 could have lots of miles, you didn't say and I don't know the environment where you operate, such as desert or swamp. I know you have been in the carb a bunch but a couple of thing to look at and you don't need to pull the carb to check. Does the carb slide lift all the way, and is the needle, some people call it the metering rod secured, meaning it can't be pushed up in the slide. While we are on the carb, there is/was a rubber flap at the back of the fuel tank that I have seen plug the intake, the intake tube should stick up through it. You may also have a plugged exhaust, the end pipe comes out and you can check it, they can be a bitch sometimes if they are really stuck. Don't buy clutch parts yet, if it is clutch, and it doesn't sound like it, it will probably be the shoe clutch, it drives off of the crank. Also what does the spark plug look like, is it sooty or white or wet. Is there any popping or sputtering, or just the rpm fluctuating?
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post #5 of 33 (permalink) Old 05-15-2011, 10:23 PM Thread Starter
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It has about 21,000kms (13,048) miles on it. I'm in Newfoundland and do mostly gravel road driving with ocasional bog.

Carb slide is good and needle is succure. My rubber flap isn't over the intake.

I will remove my exhaust tomorrow and check it. Though it seems to be blowing exhaust like normal.
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post #6 of 33 (permalink) Old 05-15-2011, 11:33 PM
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No power 350

I have reread the first post several times. It seems that you were drawn to the clutch, that may be correct. You can watch the action of the belt/clutch assy if you are carefull, get the wheels off the ground and make it secure, really! Get the big belt cover off and rev the machine and see if the belt action is correct, if the shoe clutch is slipping and or the belt can't get to top gear so to speak the machine will come up on e the rev-limiter and it will feel almost like a missfire. The carb, flap and exhaust are all problems I have seem many times, I have also seen slipping clutches, the shoe clutch, not usually the clutch pack, meaning the discs, also if the belt pulleys can't function correctly it is almost the same as a slipping clutch. Make sure the machine can't fall off the blocks and you can watch the belt action. The finger on the plug hole has allways been a good test, but if you can borrow a compression gauge it might be helpful. You have a jim-dandy of a proplem so far.
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post #7 of 33 (permalink) Old 05-16-2011, 12:21 AM Thread Starter
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I'm unsure of what you mean by the "belt". I know of no belt on this machine. Also, if I remove the clutch cover, there will be no oil in the engine, so I wouldn't want to run it.

My orignal centrifugal (shoe) clutch looked very worn and had many pits and chips gone from the clutch material. The 2ed hand one I bought, although in better shape, appears to have even LESS material on the shoes than the orignal. I may have to chuck out $300 for a new one, which I don't mind, IF that is the issue.

Fixing cars is SOOO much easier...they usually have a computer to tell you the issue...or at least a hint lol
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post #8 of 33 (permalink) Old 05-16-2011, 12:57 AM
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350 No Power

Sorry about the Belt issue, my bad. Afterall you did say Big Bear. I screwed up and got to thinking of the Kodiak and the Bruin models. I feel as dumb as a box of rocks, no don't run the engine with the cover off, sorry about the lapse of brain use there. Before you order the new shoe assy get the spec for the thickness of the friction material and measure it. I don't have my book with me now or I would post the spec, won't be back in town for 5 more days. It might still be exhaust issue, at least that would be cheap. Working on cars is sooo hard for me!
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post #9 of 33 (permalink) Old 05-16-2011, 01:53 AM
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350 No Power

Read 1st post again. This problem started suddenly, is there a lot of cam chain noise? I have seen a few jump time and have no power. It's easy to check, pull cam cover on LH side of head, 2 screws, and pull the inspection plug on the LH case cover and see if the marks match up!
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post #10 of 33 (permalink) Old 05-16-2011, 09:37 PM Thread Starter
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Did some more tests today.

Compression is great and built up fast.

Timing is spot on.

My spark however....refuses to jump anything over 2.5mm and the manual says minimum of 6mm so I guess I'm looking at a new coil. Also I'm trashing the 2ed hand Centrifical clutch in favor of a new one....$300....ouch....

Anyone know how to check my exhaust for restrictions? So I just remove it and blow in it or wa? lol
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