kx125412

Member
Mar 30, 2006
341
0
My little brother picked up a 1985 YZ125 thats in ok shape. The thing just has no power at all. Him and my dad believe in if its not broken don't fix it so unless it needs to be replaced it won't. The topend feels like its got good compression, I checked the powervalve and its moving, although it is a little sticky but it moves the whole rotation. Reeds I think are done, its hard to start. But when you're riding it has no hit and it won't even spin the tire and theres no chance you'll get that front wheel up. It revs out slow and theres no power on the top end like a 125 should have. That's why I checked the powervavle but its working. It could use a topend probably and reeds but I'm not fixing it I just want to know what you guys think. They're mixing it at 32:1 just regular gas. The jettings probably stock, when I rode it it felt a little rich but there was no lean bog anywhere. It feels the same as his old xr75, goes about as fast and almost as gutless. Both smoked they just sound different :)
 

Agitator

Member
Dec 21, 2005
210
0
just do a quick compression check with one of those gauge testers and see what you see (?)
I'd be surprised if a new top end job didn't get it back in shape. Even if you just honed the jug and did a new ring?
 

kx125412

Member
Mar 30, 2006
341
0
I live in BC
Haha, my dad said they'll cough up the cash when the bike goes "cough" :bang:
They'll have fun picking chunks of piston skirt out of the bottom end. Oh well not my bike.
 

ysr89

Member
Dec 4, 2007
108
0
kx125412 said:
I live in BC
Haha, my dad said they'll cough up the cash when the bike goes "cough" :bang:
They'll have fun picking chunks of piston skirt out of the bottom end. Oh well not my bike.


Gotta love that logic, "Instead of paying some money now to fix it, we'll wait until we can pay ALOT of money when it blows up!"
 

gb250

Member
Dec 2, 2007
16
0
I am currently bringing a YZ250 '85 back to life. I did the basic overall checks before trying to narrow anything down. New Reeds, new plug, fresh gas properly pre mixed, repacked silencer, new oil. It runs pretty good for a dinosaur, still dialing it in precisely. I found that previous owners had the carb all set out of wack, the floats were out of adjustment. Someone had been changing the needle clip position as well. I could be any number of problems, and may be an easy fix. Takes some dedication to it to get it done right. Doesn't sound like there is a big interest to fix it, so maybe you shouldn't waste your time with your brothers bike, work on you own instead :P
 

Bigdogdaddy69

Member
Feb 18, 2008
105
0
well its a 85 its not going to perform like the newer bikes. Sounds like you need piston and rings. could even be a bad cylinder thats robbing your performance. my buddy has the same bike, that was never fast either.
 

mox69

Member
Mar 26, 2007
236
0
My 1979 YZ80 could pull a wheelie with a little coaxing. It still had the "hit" even though it sounded more like a chainsaw than a dirtbike :)

It won't be as fast as a new 125, but it sounds like your missing some power somewhere.
 

kx125412

Member
Mar 30, 2006
341
0
Ya my buddy has a 79 or 78 YZ80 and it has a wicked hit and ya it does sound like a chainsaw haha. I had a 1982 RM125 and the hit on that thing was brutal. I'm used to the 250 but the 125 should have a lot more go than it does even if its old. Everyone here is so caught up with having a brand new bike when so many people just play around in the trails. If you're racing it would be a good idea but who cares how old it is to mess around in the bush you still have just as much fun.
 

Jeromeo

Member
Feb 26, 2007
187
0
Bigdogdaddy69 said:
well its a 85 its not going to perform like the newer bikes. Sounds like you need piston and rings. could even be a bad cylinder thats robbing your performance. my buddy has the same bike, that was never fast either.
must have had a junker. These bikes are quick regardless of what others say.
 
May 1, 2007
85
0
I have a 1986 KX 125 and a 1989 YZ 250wr, ride with a large group and swap bikes regularly. From what I have seen, handling and suspension is the only real benefit of owning a newer bike. I don't care if they are old or not, they still haul like no other. Definately should talk them into doing a topend and changing the reeds so you can ride together without stopping to wait for them. :)
 
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