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Old 03-10-2017, 06:37 PM
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Default 1999 YZ125 off issue

     

So I picked up an old 99 YZ125 for cheap, took it home and started my project. Long story short I have it running now but it has what I can only call a hanging idle/throttle and so I started to look for an air leak and I found it. There is a small hole on the left side of the head right where the reed cage goes in. So I plugged it eith my finger and voila problem gone. Issue is I have never seen this hole on any other 2 stroke and so I look up the parts diagram for the crankcase and find that a hose barb and hose is supposed to go on here. Refer to part number 2 and 3 9n the crankcase diagram. Anyone have any dragging idea where the hose goes or what this hole is 4? I currently have the hole plugged and the vike runs fantastic but I still want it right. Any help would be appreciated.
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Old 03-11-2017, 06:26 AM
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I have not seen the hole on OEM units, but it could have been some previous owner's attempt to make what was called a "boost bottle" back in the day, but not sure. If it runs good with it plugged, the have fun!

Paw Paw
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Old 03-14-2017, 01:35 PM
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I thought that as well but the parts fiche shows a barb and hose there and calls it a suction pipe. See part number 2 and 3 on the crankcase parts diagram for the 99yz125. I just checked the 2000 model and it had it as well.

I recently bought the barb connector and hose and was able to force the barb in place. I believe this is something that is press fitted in the factory. I connected the hose but need to know where the heck it goes haha? Any ideas?
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Old 03-14-2017, 01:48 PM
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It does not show on my parts fish. Are you sure it is a YZ 125 and not something else?

Paw Paw
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Old 03-14-2017, 01:51 PM
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It's a 99 yz125. I've rebuilt this entire motor using yz125 parts. In addition the motor stamp and frame vin indicate yz125 as well. I just looked at 2 different parts diagrams that show it. I'd post the image here but it won't allow me to get apparently.
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Old 03-15-2017, 05:50 AM
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I have gone through the parts book again and find nothing as described.
You state it is on the head above the reeds. There is nothing on the head nor on the engine cases above the reeds not on the cylinder.
The only possible thing could be the vent hose above the exhaust valves on the front of the engine above the exhaust. If that is it, it's a vent line for the pressures that build up in the valves. If that needs to be plugged for it to run correctly, you have worn out valves or cylinder. If you plug it, the pressure may cause other issues when the pressure builds up. If on the other hand it is the engine case vent line then you have a bad crank seal on the clutch side that needs to be addressed. If those are not it, then I am still at a lose.

Paw Paw
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Old 03-15-2017, 06:03 PM
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It is in fact the crank case vent. It doesn't connect to anything. You just route it down the back of the engine, along with the carburetor vent lines. Like stated above, you need to do a leak test and check the right crank seal.
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Old 03-16-2017, 08:56 AM
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The crankcase vent is existing and is in fact lower down near the back if the motor near the transmission and the hose is in fact routed as you describe.

This is right next to the reed cartoon the left.

I have a bearing going bad and currently splitting the case or i'd snap a pick. It makes no sense for this to be a vent since it is literally a hole in the intake right by the reed cage with a connector and hose barb on it. It woukd never vent anything. It woukd just suck in air and that in fact is exactly what it does

Anyone have a pic of the left side if a 99 yz125?

---------- Post added at 10:56 AM ---------- Previous post was at 10:49 AM ----------

I have a feeling that someone just tried to do some sort of stupid mod here and the part I'm looking at on the oarts manual is in fact the crankcase vent but not positive about that. It's called a suction pipe connector. On the diagram.
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Old 03-16-2017, 02:30 PM
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The crankcase breather/vent hose is attached under the reed cage below the intake.

What I'm looking at is on the left side of the intake. This hose sucks in just like it would if you put your hand over the intake and tried to kick start because it literally goes into the intake.

I guess I'll see if I can figure it out. Can't do a leak down test. I'm in the process of splitting the case and replacing bearings and seals and such anyways.
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Old 03-16-2017, 02:49 PM
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Would it be the fitting with the black rubber hose in this photo that's partially obscured by the clutch cable and running under the carb? If so it appears it is just a vent.

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Old 03-16-2017, 03:24 PM
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No but that's close. It's actually about 2 inches above that right there on the side of the intake. It makes no sense. I have never seen a hose in this location before. Currently there's just a fitting in this spot that allows you to attach a hose to it.

---------- Post added at 05:06 PM ---------- Previous post was at 04:58 PM ----------

http://www.motosport.com/ajax/oem/im...cq_4BQ2&zoom=5

See where part #2 and 3 are pointing? If I leave this hose just hanging it'll suck water right up as it pulls as hard as the intake. It coukd just be a vent but the word vent inherently means out not suck in.

---------- Post added at 05:24 PM ---------- Previous post was at 05:06 PM ----------

I think somebody had just done some sort of stupid modification on it. I'll probably just have to eliminate the whole or at least seal it or replace the crankcase or something I don't know. It runs perfectly fine when the hole is plugged. I might just leave it that way.
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Old 03-16-2017, 04:15 PM
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I did look at the parts fiche, but not closely enough. Now I see that #2 is actually the fitting for the crankcase breather and installs below the casting for the reed cage. I can't imagine why someone would drill a hole in the intake like that, unless it was as PawPaw suggested and formerly used to connect some sort of boost bottle contraption. If it were me, I'd probably pay someone to weld the sucker closed to eliminate any chance of a leak or dirty air entering the engine.
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Old 03-16-2017, 04:38 PM
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That's what I figured. I have never seen any sort of fitting on the side of the intake like that. Thanks for digging as deep as I did and confirming what I thought all along. Stupid people should never own a dirt bike lol. They could have put a tube into the intake boot like boost bottles used to be installed.

Last edited by Eligonzalez2010; 03-16-2017 at 08:31 PM.
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Old 03-16-2017, 07:08 PM
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Short sheet metal screw with silicone sealant !!!
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Old 03-16-2017, 08:31 PM
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I was using a flange bolt with sealant and I threaded the hole lol.
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Old 03-17-2017, 09:52 AM
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Quote:
Originally Posted by Eligonzalez2010 View Post
I was using a flange bolt with sealant and I threaded the hole lol.
That with a liberal dose of thread locker or some JB weld to eliminate the possibility of leaks is probably the best affordable solution. I'd just make sure whatever bolt you're using isn't protruding into the intake tract.
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