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Jetting tips

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Hey guys I'm working on a 2000 Yz 125. With a new plug in the bike starts with no problem. After 2 min of riding the bike completely bogs down and will not start back up. I remove the plug and see it's very oily (black). The bike did hit top speed while I was riding also. I remove the carb and the main jet is 410, pilot 40, Needle 6CHY3-75, and slide is 6.5.. Any know the factory jet specs? Or tips how to fix the problem.

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Did you measure the float / fuel level ?

'seems to' isn't precise enough.

 

With an engine that old, if you don't know it's previous maintance records,

installing new crank seals can avoid many headaches in tuning or even an engine seizure

if the seals decide they've be in service for too long.

Edited by mlatour

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It's the right hand crank seal (behind the clutch) that, if damaged can suck in gearbox oil.

The only way to check it is by a crankcase leakdown test.

Left side crank seal if damaged would make the engine run lean (suck in air)

 

A too high float & fuel level would make the engine run super rich,

perhaps less apparent when the engine is cold but once warmed up, enough to foul the plug.

Edited by mlatour

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Yes sir you are you right once the bike warms up the plug fouls instantly... I don't have a leak down tester is there another way? Or should I lean more towards the float height? Can I just remove the clutch assembly and inspect the seal? Thanks for the help

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You can make yourself a leakdown tester for about 25$, (a must for anyone who works on a 2-stroke)

you just need a bicycle tire pump to pressurize the crankcase only to about 7psi.

 

Rule of thumb is no pressure loss during a 15 minute test at 6psi,

recently checked mine and got less than 1psi loss in over 60 minutes under pressure.

 

Not sure about the 2003 model year YZ125 engine design but some models you can

replace the seals externaly, other you have to split the cases.

 

If the crank seals are original 2003, even if they aren't leaking they're likely due to be preventatively replaced anyway.

 

 

There's no reason not to check the float & fuel level as well, cost : 0$

Edited by mlatour

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Is the a place that sale or DIY tool to measure the float height. I'll be out today look for the material to make the leak down tester.

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My service manual ('10) states a 'Yamaha Fuel Level Gauge Adaptor'

but I've made my own with a spare float bowl drain plug.

 

Drilled a hole in the bottom of the plug and inserted a lenght of clear tubing.

 

When the tubing is held verticaly next to the carburator (can be checked either on of off the bike)

you can measure the fuel height versus the bowl's mounting flange, just like the Yamaha tool.

Edited by mlatour
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Hey thanks you are the best. Now I have removed the right side case to inspect the seal. The seal wasn't sitting flush, it was pushed inward towards the bearing. So I removed the seal and I have ordered a new one. This should help solve most of my plug fouling. While disassembling the right side case I noticed a few of the case thread holes where damaged. The 8mm won't tighten you can just pull the bolts out. Can I tap that hole to another size?

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Best bet is to fix the threads with a Helicoil insert,

local auto part store will be able to get that for you.

 

Bring them a bolt so they can check the thread pitch.

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Now I have the seal fixed and the plug fouling has stopped. I have the bike idling perfect and she rips instantly but as I ride I can feel the power but she Boggs almost halfway and beyond throttle I'm confused on what to adjust. I have the need clip next to the top where it would be leaner. Any help any one

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