03 yz125 carb help

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4/10/2018 7:14 PM
Edited Date/Time: 4/10/2018 7:29 PM

I’m confused. Last week I bought this yz brought it home idled and reved up fine. Rode it around and ran fine. Adjusted floats because it leaked a bit of gas out of the overflow ran and checked jetting. Pilot is 45 and stock is 40 so really rich (5000 ft elev). Was gonna wait til I got to the track and got the bike warm to adjust fuel screw. Went and rode it it ran great. Forgot to check fuel screw. Noticed a little bog while riding and it did it even more brought the bike back and fuel screw was missing it fell out. So I loaded up and went home. Bought a new fuel screw and took it to the track this weekend. It just really boggy and I think rich off idle and a little higher like 1/4 throttle. It would sit and idle tho but really low idle. Figured it was too rich. Ordered a 37.5 and a 35 pilot and tried them both. Bike will not idle and not run right at low rpm. Turning the fuel screw does nothing and the idle screw is all the way in. It will not start unless you give it gas. Took the pipe off and looked at the piston and cylinder from what I could see it looks ok.

Could the pilot circuit actually be clogged and it be real lean. Seems rich to me but what do I know I guess. Have not tried to clean the carb again yet. That is next on my list. Guess it could have sucked something in through the fuel air screw hole when it fell out.

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4/10/2018 7:29 PM

First thing to do is a compression test and a leak test. If both show ok, then clean the carb.
When jetting gets to be confusing there is normally another reason causing this issue. Air leaks, bad reeds or bad crank seals can normally be the route cause if leak test and compression test are good.

Paw Paw

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4/10/2018 7:51 PM
Edited Date/Time: 4/10/2018 8:08 PM

I’ll try a comp test maybe this weekend. It is smoking a lot and it is smoking out of the power valve hose some. It is starting to leak oil out of the exhaust and when I changed the plug it looked wet.

It could be something not carb related but I feel like it’s not. Why would it run so good then just not run good at low rpm and not idle. It still rips up top. Something has to be up with it.

I just thought if the air screw pathway got clogged that would make it really rich. It runs and idles like if you were to run the pilot screw all the way in.

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4/11/2018 6:55 AM

Guess for a leak down you gotta build some contraption out of crap from Home Depot.

I’ll try the carb clean first, makes sense the air circuit that the air screw goes into and is apart of is clogged. It ran fine until it fell out then started running worse. Could be something else but I’ll start with the easy stuff.

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4/11/2018 7:08 AM

Maybe some videos would help. These are a week apart.


Running good

Running bad

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4/11/2018 11:47 AM

On the parts diagram the air screw just shows the screw and a spring. When I ordered it it came with that plus an o ring and a small washer. I figured it went oring-spring-washer-airscrew. Is that what I'm supposed to do or should I not be using those parts or in a different order.

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4/11/2018 12:54 PM

lcgordon711 wrote:

On the parts diagram the air screw just shows the screw and a spring. When I ordered it it came with that plus an o ring and a small washer. I figured it went oring-spring-washer-airscrew. Is that what I'm supposed to do or should I not be using those parts or in a different order.

Airscrew,spring,washer then oring

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4/11/2018 1:14 PM

That actually makes sense. The spring would tear into the o ring maybe if the washer was not there. Thanks

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4/11/2018 3:03 PM

No problem I just did mine and that oring was hard as a rock and stuck in the carb.

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4/11/2018 8:16 PM
Edited Date/Time: 4/12/2018 6:05 AM

Got it fixed. Thanks guys for the help. I bet it sucked in something when the air screw fell out when riding. Do have to buy a new air screw set up because I ripped the small o ring.

I need to trust myself a little more, I get so stressed when I don't know what the problem is but I knew what it was. I don't do all this reading and researching for nothing.

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