Beartracker 250 timing - Yamaha ATV Forum
 
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post #1 of 10 Old 03-02-2016, 01:38 PM Thread Starter
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Beartracker 250 timing

Ok- I got a whole new top end.
My original problem was it somehow "lost" the timing gear keeper/dowell and the piston smacked the intake valve, lost one of the valve keepers. I bought a new valve and keeper and dowell, put it back together and it ran fine for a day and just bam! stopped running. Checked it out and no compression. Took it apart and this time it smacked the exhaust valve- must have jumped time?
Now I bought a jug, piston, and head. I have it all together, but am worried about the timing. There are three timing marks- turning the flywheel counter clockwise theres one thick mark, then the thinner F mark, then the thinner T mark. I timed it off the T mark (last one going counter-clockwise) it started right up. I adjusted the valves, but when I turned the cam gear one full turn, the valves seemed the same as when I checked it last, I never got to an exhaust stroke. Is that one turn on the cam gear, or one on the flywheel? The exhaust got hot right away, the throttle response is terrible. It will rev up and not come back down, and it wouldn't take fuel. I adjusted the air screw and ran it awhile and got some clean gas through it, it runs better but I am worried I don't have the timing set correctly. I cannot locate a good pic of the correct timing marks. Do I set it off the thick line or the T mark?
It also seems to have a lot of timing chain noise. I just want this piece to run I'm tired of working on it!
Thanks
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post #2 of 10 Old 03-02-2016, 06:16 PM
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It says the thick line next to the T... So you might be a tooth off on timing..

Here is some reading material -
Zippyshare.com - YFM250.pdf
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01' Raptor 720, Stage 2, FCR'd
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post #3 of 10 Old 03-04-2016, 01:56 PM Thread Starter
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I have that downloaded- but the first line is the heavy line- the next two lines are light, one with the F and one with the T.
If I tried timing off the heavy line would it hurt anything?
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post #4 of 10 Old 03-04-2016, 04:28 PM
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The instructions say to time off the line next to the T, not the T, which is what I think you are calling the heavy line.

I would try to re-time it with the heavy line. Just make sure to rotate the engine 2 full revolutions by hand.

The F is probably an ignition reference.

01' Raptor 720, Stage 2, FCR'd
97' 250 Vitos Blaster
06' Rhino 450
94' Banshee T-5's, Vforce, ported, Cool Head, 2-1
06' Wolverine 450 - Stock!
06' LTZ 440
94' Vmax4 750, 96' 600 MountainMax, 07' Nytro(b00sTed)
06' Vmax 1200
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post #5 of 10 Old 03-05-2016, 09:38 PM Thread Starter
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As the flywheel comes around counter clockwise, first there is a heavy line, then about maybe 1/2 to 3/4 of an inch there is a lighter line with an f next to it, a little farther there is another light line with a T next to it.
From what I have read from timing these and other Yamahas, you use the last line you see going counter clockwise, or the line with the T next to it. I did but I cannot seem to find the exhaust stroke- every time the mark on the cam gear lines up on top the valves measure the same. I just want to be certain I have it correct so not to do any damage to the new top end.
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post #6 of 10 Old 03-05-2016, 10:27 PM
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pull the plug and put your finger over the hole and turn the motor over. when you feel the compression make a note of the flywheel position. if you can see in the plug hole rotate the engine until the piston comes to the top again that will be tdc on the exhaust stroke. if you cant see in the hole use a drinking straw or a wood dowel to feel tdc
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post #7 of 10 Old 03-11-2016, 12:11 PM
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sorry but i just joined and not for sure how to make a new post. So I'm going this route. I have a Yamaha 250 bear tracker that I put a new carb on and new intake manifold. It runs like crap. Spits and sputters and backfires. Plus the exhaust gets glowing red. Could all this be a stuck or burnt valve? Just looking for any suggestions. I'm not the best mechanic. Thanks
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post #8 of 10 Old 03-11-2016, 09:29 PM Thread Starter
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Thanks Cory52000- I was overthinking it. I have the handy dandy inspection camera that looks right into the spark plug hole and I can see the piston come up and change direction.
I found most of my problem was a weak battery- I borrowed the warrior battery and it straightened out. Now the only problem I am having is it has no torque at the low end. I'm pretty sure that is in the carb. We are at 47000 feet and I think I need to re jet it somewhat or moove the needle.
baugusbrent - I would start with searching for a thread on adjusting the carb- these things are sensitive lol. Then check it is timed correctly. The exhaust runs pretty hot naturally, glowing may be excessive though. Mine totally jumped time ( somehow lost the timing gear dowell) and caused physical damage to the valve. Good luck! This is the pickiest thing I've worked on besides my Bayou.
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post #9 of 10 Old 03-12-2016, 10:58 AM
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baugusbrent are you sure you got your new boot in correctly. a broken or misaligned boot will cause symptoms like that or you are simply to lean. do a compression test to rule out a valve problem
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post #10 of 10 Old 03-12-2016, 11:01 AM
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viii take a look at your plug to get a place to start that will tell you if you are lean or rich. if i had to guess i would say rich at that elevation.
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