2003 Yamaha YZ 125 - Page 4 - Answered Questions & Fixed issues
Where is a power band at on a 2 sttroke
The 'poer band' is not an object in the engine. It is a term that refers to the RPM range in which an engine produces the most power. All engines have a power band but it is a term that is most commonly associated with a two stroke because almost all other engines have a very smooth transition of power yet the tuned, performance 2-stroke engine has a very clearly defined RPM range where it produces substantially more power - hence the term.The power band in a 2-stroke is typically in the upper RPM but it can be moved and altered by changing the compression of the engine, the weight of the flywheel, the carburetors settings, the port timing of the cylinder, the shape of the combustion chamber and the exhaust tract among other less popular mechanical alterations.I hope this clears things up.
Do I need a new part or is this a regular problem with these bike?
If there is no hose or restriction, the cylinder will do that. There is no check valve or other device to prevent backflow - it has to backflow otherwise the brakes would not release. If it is not producing pressure then it may need to be either cleaned or rebuilt. These are simple to rebuild.
How to bore out top end of motor? and how much
Honestly - it's just as cost effective to just buy a new cylinder complete from Yamaha - unless you have a lot of porting done to your cylinder. The cylinders are plated and you typically don't bore them - you have them re-sleeved.I have raced semi-pro for many, many years (AMA District 13, A-class). When I raced 125s (1998-2002) I would usually go through 6 to 8 cylinders per season and I would rebuild the engine after every race (every week). I never bothered getting the worn cylinders resleeved because the sleeves cost almost as much as a new cylinder from Yamaha.Price out a new cylinder then price out the re-sleeve. You'll see there's only a slight difference. I recall the new cylinders being about $245 and a sleeve was around $225.Once you get it rebuilt, keep the ring fresh and make sure you run at least 28:1 mix. I raced at 26:1 to get the engines to last. They are single ringers and the piston ring just doesn't last. Yamaha recommends changing the ring every 2.2 hours for maximum output. I couldn't get 2 hours on a motor running 32:1, so I switched to 26:1 for more lubrication and better sealing of the ring. Long story.I hope this helped.
Bike dose not pick up
Sounds like it's trying to sieze if it's fluctuating and won't wind up. You may have to pull your cyledar back off and mike it to see if it is out of round and within specs.
I DONT KNOW WHAT MY AIR FULE SCROW AND IDEL SCROOW
Hi..both screws r on outside of carb your air flow screw is the bigger of the 2 with a spring on it usually by top where throttle body is.. Outher is kinda set in on same side b careful u dont loose lil washer and turn small turns to fix your issue.good luck bud..
I have a Yamaha yz
This is telling you your oil and water seal need replacing ASAP do not ride until fixed as you will seize bottom end guaranteed !
there is small seal each side of your water pump impeller when you take the impeller out replace both even if only one needs doing as you will be going back to replace the one left soon after as they always go together..
Most people would not do this repair without replacing the impeller as well - usually the impeller starts to wear groves where it spins inside the seals then damages the seals So you get the theory behind replacing the whole lot as old impeller can damage your new seals
The seep hole is designed to give you warning of burst seal before its way to late as without the seep hole leak you would have no idea you are leaking coolant into the motor
You can do your self its a bit of work but not complicated - if you do your self don't forget to change your engine oil couple of times after first few rides reduce any risk of having coolant inside it where it should not be
good luck regards Jamie
Is it ok if i
Not sure what your question is from how it's written?
But what I interpret is you mix your fuel in the gas tank of your bike - to this the answer is simple
NEVER DO THIS always premix in container then add.
If your asking what ratio to mix then it depends what riding you will be doing, race or recreational very hard and fast or just slow riding but most would run 40:1 to 50:1 ratio in a YZ125cc
regards Jamie
How much oil can it hold
Hi,
It needs 800ml( a quart ) of lubricant, don't forget to clean or replace the oil filer.
Hope that helps you!
I just got a 1994
if the plug is sooty your float is set wrong the air filter should have oil on it to catch dirt.sounds like a carb problem although it could be the power valve
My yz 125 starts first
you might want to check your air filter first .. mine was doing the same thing ,.. and i checked the air filter and it was covered in oil so it wasnt getting enough air when i tried to take off ,.. if the air filter looks good , you may want to pull your spark plug and look at it ,.. if it is covered in black it is time for a new one .. or a really good cleaning ,.. i found a wire brush and penetrating oil works well ,.. blow it out with compressed air and wipe off all that you can before you stick it back in ,... other than those i hear the rings are only good for about 20 hours (non-racing)
thats where i would check next ,.. let me know if this helps =D
[email protected] locked up
Two things that commonly cause a lockup are the kick start mechanism and bent shift forks. If the engine kicks over properly then the starter can be ruled out. That leaves bent forks. I don't recommend the repair be done by the home mechanic. Some special tools are needed and the shop will charge more to fix a basket case than if you just take the bike in. Check the estimated cost for the repair. Now may be a good time to trade it in for a new bike.
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