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Discussion Starter #1
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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Lack of power 350 SE

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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Discussion Starter #3 (Edited)
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.
 

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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 ***** 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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Discussion Starter #5
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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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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Discussion Starter #7
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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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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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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Discussion Starter #10
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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exhaust is two bolts on the frame under the fender, and 1 off the straight pipe. all easy to get at. just turn and wiggle it out. just shake it out. youre probably ok. just a little rust...
see if someone can test your coil before you buy it, you might be looking at a new stator instead.
just a thought...
 

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yes. i was told that the 350's had bad stators for a number of years. the guy i got my bike from was adement it was the stator. he had given it to his brother to look at and his brother bought all new electrical parts, cdi box, coil, etc. i took his advice and just bought the stator. and it was the problem. there was spark with the old one, but dim and inconsistent, it should fire like a machine gun, and very blue.
 

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350 No Power

On the issue of the exhaust, because of your reply I will guess that you were unable to remove the baffle in the end of the muffler. If that can be removed you can look inn the muffler and see the spark arrestor portion and see if it is plugged. In older machines I was unable to get some of the baffles out, they are just stuck, if your's is stuck here are a few idea's. Ride the machine and get it fully warmed up, then carefully see how hot the muffler is, if the muffler is a lot cooler at the end pipe you may have a problem. I have see the support members in the mufflers break and restrict or clog the muffler, this is usually associated with a rattle, and again very hot at inlet to muffler and a lot cooler at the outlet end. Take the muffler off and shake it, does it rattle? I have also used a garden hose and put the water in the front and see how well it comes out the back, a clean muffler would flow water like trying to fill a bucket with a huge hole it it. Your test ride and impression will be the factor in a slipping clutch, I just not so sure that is your problem yet. Your description really sounds like a power issue. Maybe hold off on the money for new clutch. I doubt the coil is an issue, it starts, I have replaced many stators, almost never a coil, usually spark gets stronger as rpm's climb. Before you think coil try a new plug cap, they are cheap. Also you can make a cheap spark tester. Get a short length of same dia plug wire, unplug plug wire from coil to plug cap, put new wire into plug cap. put the two ends into a piece of clear fuel line that gives a tight fit, push wires together and start unit and start to pull wires apart and watch spark, and see what the spark looks like at higher rpm. You got a good one here! Good luck!! Reply with results, I am curious.
 

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Discussion Starter #15
Ok, I went and ordered a new stator, coil, and a new cintrifical clutch. My exhaust didn't seemed plugged but the muffler was just one I made up outta a old Tri-moto muffler and it was getting pretty rusty so I ordered a universal muffler too.

Let you know how it goes when the parts get here.
 

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No Power 350

The minimum thickness for the friction material on the shoe is 1.5mm in the illustration in the Yamaha man this is measured from the metal portion of the shoe to the top of the friction material. In the drawing it shows the deminsion about the same as the depth of the groves that are in the shoes. I found the earlier pictures you posted and the shoe was worn past the grove, that is worn out! A worn clutch will cause the engine to overrev and actuate the rev-limiter, this will be a missfire plain and simple. Many of the machines that I have worked on the clutch was slipping before it reached the bottom of the groves!

I was not aware that your exaust was not stock, I have seen stock exhaust systems plug, and on the Warrior the muffler will break on the inside and cause exh flow problems. Owners jump the warrior but not the Big Bear.

Stator failures fall into two groups, charging problems and running problems. My personal experiance has been that running problems are with hard starting, the pulse coil, a part of the stator if the run portion of the stator. Most failures make the machine hard to start but it will run OK once it is running. The charging portion is of course self explanitory, the darn battery goes dead!

If you purchased an OE stator from Yamaha you paid a price and I hope that you really need it. There is much talk about stator failures. Some make it sound as if they just go bad, heat is the devil that kills these components, almost every machine that I replaced a stator in had a plugged oil cooler. If your stator is bad please look at the oil cooler and make sure that the fins/vanes are clean. Even though I am aware of this I recently had to put a stator in my Rhino, the oil cooler and radiator were full of grass stems. I knew better, oh well.

I hope that the 350 will run well after this!!!!
 

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Discussion Starter #17
I would NEVER buy an OEM stator, lol. I got one on Ebay for $87 and a coil for about $30. My quad NEVER started good since I had it. Always cranked forever to get it going the first time. I put an Iridium plug in it and it helped alot but it never started with a push of the button like my uncle's Bruin. Perhaps this will fix that.

The clutch is OEM though so it was like $270 but I found an online coupon and basicly got the shipping of it free.

I'll take a look at the cooler tomorrow as I've got it all apart now anyway untill the parts get here.
 

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when you check the timing with the head/valve cover off and the screw out plug at the pull cord, what is the mark supposed to look like at the pull cord? i have looked and i know my eyes are bad, but i have a flashlight and still nothing. LOL
 

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Discussion Starter #20
There is an "F" mark and a "T" mark. Just the letters, one spaced a little ways from the other. Line it up on the "T" mark.
 
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