Carb is driving me mad!

Joined
Oct 18, 2003
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#1
Okay.. here's the problem.

I picked up my 04 YZ125 a few weeks ago, broke it in properly, and it ran just grand.

The weather remained the same, in the 60-70's, medium humidity, and I'm alittle above sea level.

A week or so later I notice a 'burp' close to full throttle, I assumed it was the main jet, but I was then directed towards it being the float. I raised the float, and the problem went away up top, but it came back. Except, it was down low. The bike responds horribly when I wick it wide open off idle, or slightly below idle.

The bike I had before this, a 2001 YZ80, never did that. It responded perfectly. The only jetting issues I ever had with it was the needle, which I raised. It runs flawless, and it's practically stock. My 125 however, as I said, is a different story.

When the bog wouldn't go away, I assumed that either my pilot jet was to rich or to lean. I tried both settings. They both help, the leaner than stock pilot jet, and the richer than stock pilot jet. But in no way get rid of the bog problem, it still remains.

Also, with the new pilot jets, I can't adjust my air screw correctly because my idle remains the same until it is turned all the way in.

Also, the bike does not bog down low with the choke in, but up top it's terrible.

My second problem is the erratic (sp) noises I get when I let my bike idle for no more than a few seconds. I will open the trottle and at around 3/4 to full throttle, the bike pops, breathes in, and makes a terrible noise like it wants to die. If I hold the throttle in for a few seconds, this goes away. All the while, the bike doesn't smoke much.

I also noticed that the bike seemed to be getting pretty hot when it made these noises. Because after I turned it off, I looked down at the bikes shadow on the ground, and could see the heat comming from the pipe. The silencer also smokes after it is shut down.

My spark plug is blackish, but not carbon fouled. Sometimes it is brown and looks great, but the problems are still there. (I have gone through many spark plugs) There is no signs of it being extremly lean.

Here are my settings as of now..

Pilot Jet- 42.5 (standard is 40)
Needle- Stock, clip at second position (Stock is 3rd)
Main Jet- Stock, #410

Thanks.. I'm going riding tommorrow, I hope you guys can help.
 

marcusgunby

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#3
Sounds like a bad crank seal to me-its not unheard of on a new bike-they cause some very erratic problems and are not easy to diagnose.
 
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Oct 18, 2003
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#4
Is the crank seal a specific part? Like a gasket? Or are you reffering to the sealing of the cases?

If this is the problem... Would it require me to split the cases?
 

marcusgunby

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#5
I would take it back to the dealer you bought it from, as it sounds like it has all sorts of different symtoms-or set it back to std and start again.
 

NGE

Uhhh...
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Sep 6, 2003
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#6
dude, it's an '04 .... bring it back and make THEM fix it.... wish I could do that with my '82...