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Hi, I recently bought a used 2014 Yz250f (efi bike) and i have been having a problem with it. So i bought the bike from a guy who raced motocross, he kept the bike in tip top shape. When i got the bike, it had a fresh top-end with a high compression piston, and stage two hotcams and a aftermarket exhaust systems. I race a mix of woods and moto races so i figured i could just add a few things for the woods and it would be set to go. When i was riding the bike before buying it, the seller mentioned that the bike almost "hesitates" when going from low to high rpms, he said that this had something to do with the new sprockets but to just stay on the gas. i bought the bike not thinking much about that because it was all around a really nice bike but now i cannot for the life of me figure out what is a causing that bog. On a moto track you hardly notice it because your always riding in the top end of the rpm range, however in the tight woods it makes the bike difficult the ride. It almost feels like there is a gap inbetween the bottom and top end powerwise, and you have to roll on the throttle real smooth in order for it to not sputter. If your going slow and then try and grab throttle quickly (to get over a log for example), it sputters out and there is no power. I tried giving the bike more bottom end power by adding a bigger sprocket, which gave more bottom end but didnt make the bog go away. Then i bought a GYTR Power Tuner, thinking i could retard the Ignition timing and move the power to the bottom end. I haven't gotten to test it a ton yet, but so far maps have helped take away the bog. Aside from that the bike runs perfectly, i have looked online and found no one else who seems to have had this problem which is why i am posting this. Any ideas would be greatly appreciated, as i have no clue what to do next, Thanks.

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Don't change anything from above,   but did you say you retarded the spark in order to improve your low end response?

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8 minutes ago, ossagp said:

Don't change anything from above,   but did you say you retarded the spark in order to improve your low end response?

Yes is that not what i was supposed to do?

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If you already did that,  you may want to undo it.   Advancing the timing gives you more low speed response,  and takes away some on top.  You trade  heat in the cylinder to heat in the exhaust side of things as well.    Having that tool to do those changes makes me want an injected bike.  I would sure encourage some thoughtful play there.  Nice way to get your setup just where you want it. 

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I have close to the same setup. Compared to a stone stock bike, the cams lost a little right off idle hit, but I would not come close to describing it as hesitating or missing. Below is a link for the post I wrote about the cams. If you read through it, you will see a map I came up with that works pretty good. It basically a mix of the bottom end hit map and the GYTR head map.

https://www.thumpertalk.com/index.php?/topic/1200570-2014-YZ250F-stage-2-HotCams

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22 minutes ago, shane5350 said:

Ok I will try advancing the timing tomorrow and let you know how it goes, thanks.

Did you try the reset as described?

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Ohiodrz400sm, thanks I will try that map out tomorrow

Did you try the reset as described?

I can't test anything further until tomorrow but I'll be at track tomorrow so I should be able to try a few out
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I have close to the same setup. Compared to a stone stock bike, the cams lost a little right off idle hit, but I would not come close to describing it as hesitating or missing. Below is a link for the post I wrote about the cams. If you read through it, you will see a map I came up with that works pretty good. It basically a mix of the bottom end hit map and the GYTR head map.
https://www.thumpertalk.com/index.php?/topic/1200570-2014-YZ250F-stage-2-HotCams

I tried that map out today and while it did not completely take the sputter away, it seemed to improve it greatly. I will most likely just keep it like that until I can get stage 1 hotcams since that appears to be the problem. Thanks for all the input.

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Yeah,  you shouldn't have to switch the cams to keep it from sputtering,  not that changing cams isn't attractive.  

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Hey just an update it turned out my exhaust packing was almost gone, put the stock exhaust with the right packing back on and it runs like new!

 

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