yz 125 hesitates need help

[JoshMeinke]

I have a 98 yz 125 i bought it a few months ago. since i bought it, it has a dead spot. when i am in first gear in the field riding around i will take off and it will be fine until mid rpm or so and then it looses all power and hesitates. when i am at the track it does it all the time and it doesnt matter what gear. now it doesnt want to ilde once it is warmed up. when it is cold it idles fine. any ideas? also i was wondering if this one is a higher performance model it has an orange frame, i havent seen any 98 125cc like this one before. it seems to be faster and a bit taller then other 125s

 

[OriginalRider]

Higher performance model?no such thing.Sounds like you should adjust your air screw or check your needle valve setting or drop your main jet 2 edit:REEDS TOO!

 

[whenfoxforks-ruled]

No way, the orange power band 125?

 

[_JOE_]

It's an old bike.....how many hours on the engine? Could be due for a complete rebuild, or simply need a needle clip adjustment. There's also many other possibilities like air filter cleanliness, silencer packing, carb cleanlinesss, sticky power valve.......

 

[JoshMeinke]

orange power band model what's that about? How do I tell if the reed are good, I have never worked on 2 strokers except for my sons pw 80 I have to clean the carb every other month or more, are the carbs about the same?

 

[OriginalRider]

JOE brought up a great point it could be getting tired.Get your self a compression tester i got one for 20 bucks.It should be atleast making 160 psi.As for the reeds its really simple take off your carb then the intake monfoild and they are right there.Usually you can tell when the piston is going when its taking alot of kicks to start and not hitting band like usually good luck!

 

[_JOE_]

The reeds should seal all the way around the petals where they touch the block. Just take them out(have a new gasket ready) when you clean the carb and do a visual, if you're not sure post a couple clear pics and we'll tell you. A compression test will only tell you how well the rings seal, a leak down test will verify the crank seals. You'll want to pull the cylinder and replace the piston if you don't know how old it is. Crank bearings are easy to check with the top end off. It might cost you soome money to put right but once you ride a fresh 125 you'll want to keep it that way. It will be night and day better than a tired one. The 2 strokes are really simple and not too expensive to fix. Let us know what you find!

 

[_JOE_]

And do a search for "powerband"........ ;)

 

[mathd]

Just like joe said.
Am pretty sure its the top end or carb pilot/needle adjustment.

 

[FNG]

Step 1, figure out what parts are in the carb, step 2, figure out what is SUPPOSED to be in there. Step 3, determine what mods are done that may affect step 1. When the carb is off inspect the reeds for damage.

Clean the carb, replace the needle/seat and install the correct jets/needle/settings for your bike then see how it runs.

If, like others have said, you don't know how old the top-end is, then it is time to replace it.

The other side to this is I had an issue where my bike ran fine at idle and putting around to 1/3 throttle until I loaded the motor and hit the power band it would miss horribly. It turned out the plug cap to wire connection was old/corroded and dirty. I clipped 1/2 in off the wire to get some shiny wire and replaced the cap and away I went.

 

[JoshMeinke]

compression read 175 cold. should be good then correct? what is the spark plug gap supose to be? what about cdi box or anything like that? i am going to tear carb down and clean that and check for wear after i clean air filter and check gap.

 

[whenfoxforks-ruled]

Is the bottom end sealed?