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86ccord's Big Bear 250 Build!

86ccord

By 86ccord
in Yamaha ATV Forum

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86ccord Contributor

86ccord

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Starting this build thread to keep up with everything on my build and hope to motivate someone!

 

I picked up this 2008 Yamaha Big Bear 250 2 weeks ago. A guy that I hunt with parked it at the hunt club for a year or so before I asked him if he wanted to sell. He said " fill my feeder and throw some batteries in my cameras, and you can have it". Sounds like a deal to me! 

I have attached some pictures of how it sat under a tarp in the woods and when I got it home and cleaned up a little. 

 

 

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Edited by 86ccord
Change title to include model
86ccord Contributor

86ccord

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After poking around I managed to get it to turn over with the starter. I found I have a no spark issue...lovely. I printed some electrical diagrams and me and my multi meter got to work. Found I had 2 out of the 4 wires chewed off on my stator harness. Decided to order a new one and install. 

 

Tonight the new stator showed up, tore it down to get to the old one. Only had ro drill out 2 bolts to get cover off. Not bad. Gonna run to store tomorrow to grab some replacement bolts. Until then, this is where I'm at

Took a picture of the old stator 

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  • 86ccord changed the title to 86ccord's Big Bear 250 Build!
Gwbarm Grand Master

Gwbarm

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Doesnt look like the tarp was doing much good there, glad you rescued it before it got worse. Your old stator which is OEM might still be good it you fix the chewed and broken exterior wires. I havent had the opportunity to work on the 250 and have never seen one only 350 and 400, is that a newly designed engine for the Big Bear only, and 2008 was getting close to the end of the Big Bear run. 

86ccord Contributor

86ccord

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54 minutes ago, Gwbarm said:

Doesnt look like the tarp was doing much good there, glad you rescued it before it got worse. Your old stator which is OEM might still be good it you fix the chewed and broken exterior wires. I havent had the opportunity to work on the 250 and have never seen one only 350 and 400, is that a newly designed engine for the Big Bear only, and 2008 was getting close to the end of the Big Bear run. 

I'd have to re-pin and terminate the plug for me to keep using the old one. I assumed it was from 2008 which is why I just went with a new one. I'll probably just try and fix it to keep on the shelf for a rainy day. 

86ccord Contributor

86ccord

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Good news! 

I found some time to get the new stator installed. The ol girl fired right up! I couldn't believe it! Although it does idle very high, Im Thinking I've got a vacuum leak somewhere. But, she's alive!! 

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Edited by 86ccord
86ccord Contributor

86ccord

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Lil update.

 

Haven't had much time But got the carburetor taken off and found the choke plunger was missing, that's probably my high idle issue. Anyways, decided to tear the carb apart and clean it up. Currently waiting on a rebuild kit to show up in mail so I can get started. Also need to locate a throttle cover or make one. 

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Gwbarm Grand Master

Gwbarm

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Good luck with the carb, with a little work it should clean up nicely, plastics look to be complete and should also polish up, with a little elbow grease. Lindseed oil works wonders on plastic oxidation. 

86ccord Contributor

86ccord

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On 10/26/2023 at 1:20 PM, Gwbarm said:

Good luck with the carb, with a little work it should clean up nicely, plastics look to be complete and should also polish up, with a little elbow grease. Lindseed oil works wonders on plastic oxidation. 

The rear plastics are in great shape. The front has some chunks missing and bad repairs on cracks. I'm going to source a new front plastic and end up painting everything at some point. 

86ccord Contributor

86ccord

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Finished up rebuild on the carburetor, ATV starts up and runs like a dream. Now I have a new problem.... 

When driving under low RPMs creepin it does great. Soon as you give it some throttle the transmission kinda acts crazy. Almost like the clutch is slipping or popping out gear. 🤷‍♂️🤷‍♂️

86ccord Contributor

86ccord

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Yeah, I followed the instructions twist until firm then back it off. Been reading, some people say yamaha clutches are very picky on the oil used. I did use a synthetic 10w 30 ATV oil super tech brand. I may go pick up some 10w 40 valvoline SAE ATV to see if anything changes. I also read my foot brake switch could be causing the cdi to throw a Rev limit issue in there. 

 

Guess I'll piddle around and find out lol 

Mech Grand Master

Mech

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Having the wrong oil doesn't make such a difference that the clutch will slip with just a little throttle. You have either a worn out clutch or it's badly adjusted or..  you say it seems like the trans is jumping out of gear.. If it was jumping out of gear it would probably make some noise, either a bang if the gear was under load, or a crashing of gears as it tried to get back into gear or into the next gear..

Try and check it isn't jumping out of gear, and then if that's not the problem you need to pull the case and check both clutches for wear.

86ccord Contributor

86ccord

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47 minutes ago, Mech said:

Having the wrong oil doesn't make such a difference that the clutch will slip with just a little throttle. You have either a worn out clutch or it's badly adjusted or..  you say it seems like the trans is jumping out of gear.. If it was jumping out of gear it would probably make some noise, either a bang if the gear was under load, or a crashing of gears as it tried to get back into gear or into the next gear..

Try and check it isn't jumping out of gear, and then if that's not the problem you need to pull the case and check both clutches for wear.

I know, i know...I agree 100%... I'm trying to exhaust all simple fixes before diving in deep. It's probably cuz i already know my answer lol 

 

Changed oil, re-adjusted clutch according to service manual, no luck. Soon as higher rpms come in it bucks and makes all kind of racket lol looking like I will take the transmission side cover off and see what's going on. 

Mech Grand Master

Mech

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That  doesn't sound like any slipping clutch !  That  sounds like jumping in and out of gear. I don't think it's going to be in the side case.. but start there and hope. Perhaps try all the gears first and see whether it jumps out of several or perhaps it's just the one gear.

I think I'd ask the buddy about whether it had been doing that before.. Just sitting around unused doesn't make them jump out of gear, and when they jump out of gear forcefully when under load, which is what it sounds like you are describing, it's normally the engagement dogs on the gears. If it's just one gear and one of the lower two gears, it might be that there is no crashing of gears nosies because  it may have a gear pressed onto a shaft which can slip under load. That makes them buck and jump but there isn't any gear graunching noises, just a squawk sometimes as the gear slips on the shaft.The manual will warn you about using a gear like that, they say not to press them off and back on the shaft more than once or twice. Not all gearboxes use that system though so that's just a guess.

Just occasionaly there will be something preventing it getting it into gear, or that spring loaded roller is broken causing/allowing it to rattle out of gear, both of which will be in the side case. If you can't see anything there in the side case I think it's going to be a complete strip down.

Mech Grand Master

Mech

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21 hours ago, 86ccord said:

"it bucks and makes all kind of racket... "

This isn't what a worn clutch does.. The clutch may be worn, but then it wouldn't transmit enough power to make the gears slip. And clutches don't make noises, and they don't grab and buck. There must be a problem with the gears I think.. or the final drive ?

86ccord Contributor

86ccord

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21 hours ago, Mech said:

I thought you might have..  easily done..

You should check whether it does it in all the gears 86 in case it's a final drive making the noise...

I tested that today. It does the same as mentioned above in all gears. Jerky and noisy. I did take the side cover off, found some metal shavings in the oil filter housing. I'm not 100% sure how to test clutch, but I'm guessing the ol tranny is shot. 

86ccord Contributor

86ccord

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2 minutes ago, Gwbarm said:

Is this a 2 wheel drive or 4 wheel drive 

2 wheel drive 

1 hour ago, Mech said:

It's not likely to have blown all it's gears.. I'd check the final drive where the driveshaft joins the engine..  

Okay. I'll take a look at that next!

Gwbarm Grand Master

Gwbarm

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Good! I like those 2wheel drive ones so light and easy to handle, fun to ride.  I would jack the rear end up to proceed with the diagnosis, then you can turn it by hand in all the gears and get a good feel of what its doing. Evan start it to get the revs up so you can better pin point the location of the noise. I hope its not too bad.

86ccord Contributor

86ccord

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3 minutes ago, Gwbarm said:

Good! I like those 2wheel drive ones so light and easy to handle, fun to ride.  I would jack the rear end up to proceed with the diagnosis, then you can turn it by hand in all the gears and get a good feel of what its doing. Evan start it to get the revs up so you can better pin point the location of the noise. I hope its not too bad.

Thanks for the tip, keep em coming! This will be the 1st time I've worked on an ATV, I'm eager to learn. I do come from an automotive background so I don't mind turning some wrenches! 

86ccord Contributor

86ccord

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5 hours ago, Mech said:

Yeah as Gw suggests, jack it up and use the brake to apply some load and then put your fingers on the final drive and see if you can feel the jumping in that cover, or the rear diff.

Well boys, we did it! It's fixed! I put the rear wheels in the air and poked around a lil. I found the Forward and Reverse lever wasn't correctly adjusted causing it to drag under a load.  Once I reseated and adjusted that, the old girl rides like a dream.....aside from that busted wheel bearing 😂😂

The build continues!

 

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