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Yz 125 problem! Should be easy fix!

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My yz 125 will do fine up till third gear you'll hit the power band and the bike will just bog down and will not start by kicking it, it has to be push started and it's not fouling plugs so I'm not sure I think it's a fuel problem or something with the needle. Please help!

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Sounds like a new top end is ready for ya the worn out top end can pull the easier gears but once your really start putting load on it it just gives out, the only other thing I can thing of that would cause that is if it was running extremely lean but I highly doubt it is

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Sounds like a new top end is ready for ya the worn out top end can pull the easier gears but once your really start putting load on it it just gives out, the only other thing I can thing of that would cause that is if it was running extremely lean but I highly doubt it is

It has a brand new top and bottom end and I'm not sure about running lean it's probably is tho

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Sounds like a new top end is ready for ya the worn out top end can pull the easier gears but once your really start putting load on it it just gives out, the only other thing I can thing of that would cause that is if it was running extremely lean but I highly doubt it is

it feels like it's running out of gas

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Did you measure the cylinder before the new top end was put in? Because if the cylinder is worn out with a new top end it will still run crappy. Also do a compression test to check. I can't imagine that it is the cylinder though because with the nickasil plating it doesn't wear out nearly as much as if it had a sleeve.

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Yeah give us a lil more here. When did it start acting this way? Were you ever able to ride threw all the gears? Is it broke in? Was the carb cleaned? Different jetting changes in between rebuilds? Do you have compression at the kick starter? Erratic idle? The scenario you are describing, are you full throttle pinned through 1-2-3 or just screwing it on in 3rd? You could be running out of fuel causing it to die on you but that wouldn't explain it having to be bump started. Check all fuel system like vent hose, petcock, or floats/fuel inlet needle in carb.

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My yz 125 will do fine up till third gear you'll hit the power band and the bike will just bog down and will not start by kicking it, it has to be push started and it's not fouling plugs so I'm not sure I think it's a fuel problem or something with the needle. Please help!

Next time the engine starts to bog, pull the choke, if the engine suddenly comes to life and accelerates then yes you have a serious lean condition, or lack of fuel . It's a good idea to dissasemble the carb for a good cleaning. Make sure fuel is also flowing freely from the petcock. Lastly it would also be wise to buy/borrow a compression gage and measure compression. Just because you have a new piston does not mean you have adequate compression. Heard your same story a million times. Most of the time it's a new piston that was used in a junk cylinder.

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Yeah give us a lil more here. When did it start acting this way? Were you ever able to ride threw all the gears? Is it broke in? Was the carb cleaned? Different jetting changes in between rebuilds? Do you have compression at the kick starter? Erratic idle? The scenario you are describing, are you full throttle pinned through 1-2-3 or just screwing it on in 3rd? You could be running out of fuel causing it to die on you but that wouldn't explain it having to be bump started. Check all fuel system like vent hose, petcock, or floats/fuel inlet needle in carb.

Everything is good now it was bad fuel

Flow

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Next time the engine starts to bog, pull the choke, if the engine suddenly comes to life and accelerates then yes you have a serious lean condition, or lack of fuel . It's a good idea to dissasemble the carb for a good cleaning. Make sure fuel is also flowing freely from the petcock. Lastly it would also be wise to buy/borrow a compression gage and measure compression. Just because you have a new piston does not mean you have adequate compression. Heard your same story a million times. Most of the time it's a new piston that was used in a junk cylinder.

. It has a brand new top and bottom end and the problem was bad fuel flow it all good now it hasn't died at all or even had trouble starts first kick every time!

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Did you measure the cylinder before the new top end was put in? Because if the cylinder is worn out with a new top end it will still run crappy. Also do a compression test to check. I can't imagine that it is the cylinder though because with the nickasil plating it doesn't wear out nearly as much as if it had a sleeve.

It has a new cylinder and piston and crank every thing is fine the fuel line I bought was to long and was causing bad fuel flow

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You do not give enough information for people to actually help you. Maybe you should get the manual and read it first.

It's fine now I bought new fuel hose line for it was to long

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It's fine now I bought new fuel hose line for it was to long

Well, I guess you found the issue, but I am at a total loss as to how a "too long" fuel line can cause fuel starvation ?

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Well, I guess you found the issue, but I am at a total loss as to how a "too long" fuel line can cause fuel starvation ?

Possibly routed wrong and was being pinched shut by something would be my guess.

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Possibly routed wrong and was being pinched shut by something would be my guess.

 

Vent valve was in Backwards :)

Rookie Mistake?

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Well, I guess you found the issue, but I am at a total loss as to how a "too long" fuel line can cause fuel starvation ?

I don't know either I just pulled the carb off and the float bowl and put the gas line on and held the carb by the peg Because I was setting on a stand and held the floats closed and opened them and it was getting good flow then I held it were it would be on the bike while riding and it was not near as good of flow so I cut the line and put it back on and it hasn't died yet and iv rode it a lot and got out of third gear so it good for now!

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