yz 125 problem

You have oil mixture ratio mixed up with what your fuel air mixture is.

You might be a little bit further along if you had read or tried a little more to accurately understand and describe the symptoms. Maybe you just haven't been around or seen and heard many engines run properly. I agree that your engine is running rich. Ie your carburetor needs WORK. Way too much fuel is getting to that cylinder from the looks. START with setting the float. I wouldn't do anything until you try that. Did you check the jet sizes? If not check them and write down the numbers and check them against the stock sizes.

I still think you need to find a dealership that can help you identify the exact engine you have , as that isnt the one that came in a 2005 here in the states. From what I am seeing yours is the earlier style.

Anyway, start the rest of the trip by finding out where the float should be set. anything else is going to be a waste of time if you want it running it's best.
will get hold of a manual then and try sort the carb out as best I can and get jet sizes I agree the float hight is wrong though as it does leak when petrol is left on without running, I still wiuld have thought it would ofnhad a lot more power even like this as have had carb problems on other bikes but they have all hit there powerband and reved higher than this....what year engine do you think it has then as its definatly not older than the 05 as the piston doesnt have a window on it which they do from 04 to the early 90s? I did try to get my engine numbers checked by a local mx shop but they wernt very helpfull
 
screw the window in the piston. lots of aftermarket pistons if ordered that way come without them. if you look at bike bandit or similar you will see that your whole engine is different than what came in the aluminum frames, that cylinder slants way further forward, and has no external clutch actuator, those were my first tipoffs.

so either your friend is about as up on motorcycles as my neighbor's bird dog, or thinks you are.

Start with the serial number off the engine with a dealer either where you live or online.
 
screw the window in the piston. lots of aftermarket pistons if ordered that way come without them. if you look at bike bandit or similar you will see that your whole engine is different than what came in the aluminum frames, that cylinder slants way further forward, and has no external clutch actuator, those were my first tipoffs.

so either your friend is about as up on motorcycles as my neighbor's bird dog, or thinks you are.

Start with the serial number off the engine with a dealer either where you live or online.
ahh you seem pretty clued up on them then do you no what number on the engine confirms the year of it I no the frame is the 10th digit.... obviously got the wrong piston in it would explain alot
 
That series is a really good motor and once running right you will enjoy it.
yeah the guy I bought it off said it went like a bat out of hell and so did a few others who've seen it go so hopefully! Just been and checked the 8th digit on the motor is infact an 04 so the mx shop gave me the wrong piston which would probably explain alot! maybe the previous owners fault though as when I spoke to the shop they said the 04 pistons had the window and the 05 onwards didnt the piston origionaly in it didnt have a window either so maybe its been running wrong all along?! will have to try the 04 piston when I can afford one!
 
Like I said, some companies don't ship the aftermarket ones cut.


Hey you might be young enough to remember this. ... Have you ever seen or heard of guys cutting or shaving piston skirts to make the bike rev faster?
When I was young, way young I heard older guys talking about it. :noidea:
 
Yep. It's called increasing the intake duration. The opening and closing of the intake pOrt was controlled by the size and placement of the port in combination with the piston skirt. Cut away too much and you were blowing back through the carburetor when the downward motion started the transfer process. Once we started using reed valves you could have basically raised the skirt up to the rings. With a case breather like all the 125's ended up with the holes and windows are really not all that useful.
 
Yep. It's called increasing the intake duration. The opening and closing of the intake pOrt was controlled by the size and placement of the port in combination with the piston skirt. Cut away too much and you were blowing back through the carburetor when the downward motion started the transfer process. Once we started using reed valves you could have basically raised the skirt up to the rings. With a case breather like all the 125's ended up with the holes and windows are really not all that useful.


That's awesome info right there. Thanks!:thumb:
 
Yep. It's called increasing the intake duration. The opening and closing of the intake pOrt was controlled by the size and placement of the port in combination with the piston skirt. Cut away too much and you were blowing back through the carburetor when the downward motion started the transfer process. Once we started using reed valves you could have basically raised the skirt up to the rings. With a case breather like all the 125's ended up with the holes and windows are really not all that useful.
Thats the piston at its lowest point, look good enough do you think? Ill check the carb out this weekend see what settings its at and if need be set it back stock! Cheers ossagp youve been a massive help you know your stuff
 

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Yep. It's called increasing the intake duration. The opening and closing of the intake pOrt was controlled by the size and placement of the port in combination with the piston skirt. Cut away too much and you were blowing back through the carburetor when the downward motion started the transfer process. Once we started using reed valves you could have basically raised the skirt up to the rings. With a case breather like all the 125's ended up with the holes and windows are really not all that useful.
just checked my carb the main jet is 440 and pilot is a 40 sounds pretty big on the main surely it should be smaller??
 
pilot sounds useable. check and see what standard was for your year. the reason i recommend checking all bikes you buy is not only so you know for future reference, but jetting down is how the unknowing deal with rising float levels. they will keep jetting down and finally after buying trick heads, exhausts and reeds decide they just cant get their "old bike" to run right, so they sell it. there are people like me that spot those and buy things cheap. there are other people that buy them because they got their ears douched with what a find and great bike is being offered. if the second type of buyer finds out through some merciful act that their problems are float related and fixes them they run the risk of burning a piston once they fix the float situation, if the leaner brass is left in.

FYI bike bandit shows 390-450 listed for sale for that one. most that I see are jetted down some from the lowest offered there as I sated earlier. yours has a different head and it is anyone's guess that that changed, so i think you would be safe to set the float and give it a try. do you know how much clearance you have at the squish area with whatever piston you decided on?
 
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pilot sounds useable. check and see what standard was for your year. the reason i recommend checking all bikes you buy is not only so you know for future reference, but jetting down is how the unknowing deal with rising float levels. they will keep jetting down and finally after buying trick heads, exhausts and reeds decide they just cant get their "old bike" to run right, so they sell it. there are people like me that spot those and buy things cheap. there are other people that buy them because they got their ears douched with what a find and great bike is being offered. if the second type of buyer finds out through some merciful act that their problems are float related and fixes them they run the risk of burning a piston once they fix the float situation, if the leaner brass is left in.

FYI bike bandit shows 390-450 listed for sale for that one. most that I see are jetted down some from the lowest offered there as I sated earlier. yours has a different head and it is anyone's guess that that changed, so i think you would be safe to set the float and give it a try. do you know how much clearance you have at the squish area with whatever piston you decided on?
I dont no the squish but it has a tonne of compression I know that! the float does need setting correctly need to go buy some feeler gauges really as it was leaking fuel everytime I take the plug out it is soaked so defiantly too much fuel getting in
 
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