Question about 2003 Yamaha YZ 125

5 Answers

I have a 04 blaster I just bored 40 rejetted the carb and removed the air box and replaced it with filter and outer wear. Now it will start and idle but when you give it fuel it will not rev it makes the sound like its sucking to much air or something.

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  • tj_2187 Jul 18, 2009

    I tried putting the air box back on the 04 blaster and adjusting the needle and air screw, but it still will not rev. Could it be the crank? Or could I have the oil mixed wrong?

  • tj_2187 Jul 19, 2009

    I'll give it a try. It has a br8es NGK plug, so I should do a br10es. Is that what you are saying?

  • tj_2187 Jul 20, 2009

    I found oil leaking out around the exhaust, it smokes real bad when giving it throttle and it stays reved up for a few seconds. But it won't rev very high. Could it be something wrong with crank?

  • tj_2187 Jul 20, 2009

    I found oil leaking out around the exhaust, it smokes real bad when giving it throttle and it stays reved up for a few seconds. But it won't rev very high. Could it be something wrong with crank?

  • tj_2187 Jul 22, 2009

    I tried to put the air box back on but the same thing is still happening! I had it bored and while the cylinder was in the shop I jetted the carb and put the filter and outerwear on it. But one thing I did not do is replace the head gasket. Could it be sucking to much air from that?

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You bored it and jetted the carb,but did you adjust the timing to compensate for the extra fuel and compression? if not that is the first step,Just back it up about 3 degrees ,Then you should unhook the self oiler if it's still hooked up and make you a gallon or so of 30:1 mix and see how that works.

Also you should check and make sure you installed the jets correctly

Posted on Jul 22, 2009

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Put the orignal air box on it and the problem will disappear, trust me on this.

Posted on Jul 21, 2009

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There are a couple things to try, first ensure that the height setting on the needle is set to appropiate level most needles have three or four grooves that you can set the c-clip at to attain the desired affect, just remember to note where you started before pulling the needle throttle piston assembly out and resetting, it sounds like the needle is sitting too low so set the c-clip down a notch this will raise up the needle and provide fuel earlier when the throttle is applied. I hope this helps. Good luck

Posted on Jul 19, 2009

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There are three things wrong, oil mix being the primary problem and your not running a hot enough plug for the new fuel mix. try a ac two steps up and you will solve your problem, lean it out just to were it turns brown and it should get it on. the other thing is air flow put a K&M filter on it to get more HP out of it. If your operating at above 5000 feet jet down, want he right size jets just send me an answer to this problem and I will fix you up.

Posted on Jul 18, 2009

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Very simple,your combustion chamber is not getting enough fuel to burn and dies out as too much air is coming in. There are 2 ways to solve this :
- either put back the filter, hence less air, balance petrol
- or you need to increase the flow of petrol going in, either move up the needle(if it has one) or you need to go up the copper like screw that allows petrol to jet into the combustion chamber.

Posted on Jul 18, 2009

  • heeman mohun Jul 19, 2009

    it's nothing to do with spark plugs here going up with br10es will not make a difference unless the br8es is faulty..You clearly have a problem with combustion, I guess it's a 2 stroke, then remove the carb and check the valve,the valve may be stuck or a a piece of it snapped or broken..

  • heeman mohun Jul 21, 2009

    it's a 2 stroke engine is it? It's quite normal to have oil around the exhaust,there is a copper ring like seal which needs replacing to stop this.Your problem is not that easy to solve, as if the engine revs ok, then there may be a problem with other stuffs like the seals are not perfect somewhere allowing air in which in turn is causing this problem,other than that sometimes faulty CDI stops the engine from high revs..I would check carb, if the throttle is pulling all the way up first,then valve, then the next step the CDI and last is an engine rebuilt.

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