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Discussion Starter #1
I recently got my daughter a bruin 250. Under normal operating conditions it has ran fine. When not in gear you can go WOT and it revs great. When in gear it bogs when hard throttling. I figured it was a dirty carb so I replaced the carb, air filter and plug. Still has the same problem. Does anyone have any ideas? Fuel air mixtures need adjusted?
 

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How old is the bike?
How many kilometers?
Do you know the maintenance history?

Is the engine doing the exact same thing after replacing the carb?
What kind of carb did you use, OEM or eBay Chinese special?

Have the valves clearances ever been checked?
When was the last clutch service performed?
Is the carb adapter boot cracked? (Boot between carb and cylinder head)
 

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Discussion Starter #3
2005
no clue
not at all
Yes no difference at all after Carb replacement
Cheap
No, Where do I get those specs?
I have no clue about the clutch
It was and was replaced. After replacing I sprayed around it with Carb cleaner and the idle didn't change. I didn't check it while throttling though.

It bogs so bad that if your standing up you almost get thrown over the handle bars.
 

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I would first start by servicing the clutches, both of them. Sticking clutches, especially one's that are not returning to lowest pulley ratio, can give you a bog.

Valve clearances should be checked. Pretty common on many Yamaha's to tighten up over time. Download a factory service manual. It's invaluable in information. Get them at tradebit.com for less than $20.
 

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How long after you WOT does it bog down. After it bogs does it come back and then repeat?
 

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Discussion Starter #6
How long after you WOT does it bog down. After it bogs does it come back and then repeat?
if you hammer on it you take off for a few seconds then it bogs. If you stay on it, it'll just sputter. If you let off then ease back into it, it'll run fine.
 

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Discussion Starter #7
I would first start by servicing the clutches, both of them. Sticking clutches, especially one's that are not returning to lowest pulley ratio, can give you a bog.

Valve clearances should be checked. Pretty common on many Yamaha's to tighten up over time. Download a factory service manual. It's invaluable in information. Get them at tradebit.com for less than $20.
I'll get to work on that as soon as I get some time. I'm guessing that the clutch and valve servicing isn't too difficult? Valves won't be a problem but I've never messed with clutches like in these semi automatic bikes.
 

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I would try running it with the petcock set to reserve if it has that position.

Can you check the ignition coil and the spark plug wire?
 

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Discussion Starter #9
Plenty of spark. You can see it sparking in daylight. I might pull it out of the shed tomorrow and see what I can get done before work. It's starting to snow here and she's wanting to play.
 

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I'm with Dezz, service your clutches. At the very least do a full service on your primary. Check out some YouTube video on the subject and you'll see its not that bad.
 

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I would first start by servicing the clutches, both of them. Sticking clutches, especially one's that are not returning to lowest pulley ratio, can give you a bog................
It appears that the 05 250 doesn't have a CVT.

That's why I'm thinking fuel supply or float level.

Bad coil...spark in daylight is not a true indication that the coil will produce steady spark under a heavy load.
 
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It appears that the 05 250 doesn't have a CVT.

That's why I'm thinking fuel supply or float level.

Bad coil...spark in daylight is not a true indication that the coil will produce steady spark under a heavy load.
Yep when I saw this last night I was confused cause I had always thought all Bruins were 350's and automaticd. Sure enough there were a couple years of Bruin 250's that had semi-auto trannies. Similar to Big Bear 250's it seems.
 

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2005
no clue
not at all
Yes no difference at all after Carb replacement
Cheap
No, Where do I get those specs?
I have no clue about the clutch
It was and was replaced. After replacing I sprayed around it with Carb cleaner and the idle didn't change. I didn't check it while throttling though.

It bogs so bad that if your standing up you almost get thrown over the handle bars.
I couldn't quite follow exactly... Is this saying you replaced the carb with a cheap Chinese carb?

If so, I wouldn't rule that out. I would always, always try to rebuild and clean an OEM carb before using a cheap Chinese replacement.
 

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Fuel/air mixtures should be adjusted as the stated turns out are a starting position & every bike is a bit different, have you removed the petcock or cleaned out the fuel tank(properly) & given it fresh fuel? If the fuel line is too long they can get a high loop in them which causes an air lock.
 

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Discussion Starter #18
It’s been a while since I last posted. No changes with the bike. I haven’t had much time to mess with it with just moving and being busy season in the liquor business. I’ve spent countless hours looking for how to service the clutches and have found nothing.
 

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I looked back through this thread to update myself on it.

Nevermind what I said about servicing the clutches. For some reason I thought it said "350", not 250.
The 350 is automatic. The 250 is not. Since you have a 250, there is no servicing of the clutches.

Since you have the same issue with 2 different carburetors, I suspect you have something else wrong.
First thing I would do now is check the valve clearances.

Intake clearance is: 0.002"-0.004"
Exhaust clearance: 0.004"-0.006"

Always adjust valves between middle to max clearance. Do not adjust them to the tight side.

If you have never done valve adjustments before, download a factory service manual for less than $20. The whole procedure is in there.

Btw, the Bruin 250 is basically an updated Yamaha Timberwolf 250 or BearTracker 250. Many engine maintenance procedures are the same for all models.
The Timberwolf was first. Then it became the BearTracker. After that, it became the Bruin. Then from the Bruin, it became Big Bear 250.
 

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Discussion Starter #20
I’ve never tried this bike but have adjusted many vehicle and motorcycle valves. Today would’ve been the perfect time since I had the fuel tank off. At least it only takes a few minutes to take off. I’ll do them tomorrow and post results.
 
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