yz125 revs crazyy without touching throttle

[erionpipe]

iv got a 99 yz125 i just picked up. The bike hasnt been run in 6 years. so i pulled the top end off, put a new piston and ring in it and cleaned the carb to perfection. first start up went good, i just let it idle to normal temp then shut it down untill the next day. Second start i rode it for a bit and realized it was wayy to rich and was spitting oil out of the silencer, so we leaned it out a bit and was running alot better. As i rode the rev would stay a little high after pulling in the clutch but eventually would drop down again. Now the third time i try to ride it as soon as i start it, it tachs itself out without me even touching the throttle. So i check all obv. things like throttle cable and reeds and all seems well. so i start it again and it idles Perfectly for about 5 secs then without even touching the throttle it tachs itself out again. I did however manage to take it for a ride and all the power is there it doesnt cut out or sputter and is smooth as silk and has no issues except when u pull the clutch in the rev goes super high. So i cant figure out why its revving like crazy without even touching the throttle. Any Ideas???

 

[IndyMX]

Cracked boot between the carb & reed block.

 

[_JOE_]

You have an air leak. Most likely a cracked front carb boot, reed cage gasket or left crank seal.

 

[daniel19805]

Mine is doing the same...but doesnt sound as smooth as it should... If the crank seal was bad wouldnt it leak oil?

 

[whenfoxforks-ruled]

The left crank seal can make it run lean. You really need to get that fixed, or it can melt your motor, top and bottom ends. Could be a simple jetting change, ignition, or an air leak. A quick look at the plug to confirm?

 

[Matt90GT]

left crank seal is dry. change it

 

[daniel19805]

What needs to be done to change the crank seal? Tuff job?

 

[whenfoxforks-ruled]

Do you have a manual, then its easy.

 

[daniel19805]

Yah I have the original manual. Going to check it out right now. Just drove her from my moms t omy house maybe 1 mile or so away. Started right up & the idle didnt jump. I had it on reserve tank though...it hasnt done it on the reserve for some reason... Then she just shut off once I stoped at my house... The battery is dead , I had to jump it to start

 

[whenfoxforks-ruled]

Your petcock and/or screen has an issue.

 

[daniel19805]

So change the petcock valve? What screen?

Can you go into a little more details please

 

[motodr9]

Try this to eliminate some causes....

First and most serious is the left crank seal leak. Start the bike and then put the crankcase breather hose into a glass of water...does it really bubble? Your seal is bad- change it. No stream of bubbles- seal should be ok.

Petcock screens clogged...pull the fuel line off the carb and put it into a fuel jug, then turn it on and observe.

Air leak (my guess too) around the reed block/carb... inspect with a flashlight inside the boots and flex 'em to reveal tears. You can also run the bike and spray carb cleaner or propane next to the boots- if engine speed increases you found your leak. Inspection is the best way though.

You leaned out your jetting after breaking the new top end in? Is it possible you went too far?

 

[Matt90GT]

a yz125 does not have a reserve on the petcock.

So either you have a WR type of petcock, aftermarket or not a YZ125.

TTR125 maybe????? It has a reserve.

 

[whenfoxforks-ruled]

Nice Matt, but I am not for sure if Daniel19850 the thread hijacker has a YZ even? May be a ttr?

 

[1SWEETYZ]

Check the routing of your throttle cable, I have the same bike and it did the same thing, turns out its too much tension on the cable which makes your bike rev really high

 

[daniel19805]

I have a 1989 125NX enduro.

4 stroke

 

[whenfoxforks-ruled]

I have a 1989 125NX enduro.

4 stroke

What company markets the NX?