2008 Yamaha yZ125 - Answered Questions & Fixed issues

Yamaha YZ400 E Owner Manual

I don't have an exact for your model but resistance issue will be very easy to spot as when you test you will get usually zero as the reading if faulty
roughly speaking you would expect 240 - 380 and 720 - 1000 and 40 - 66 on the three pairs of wires coming direct from stator if you get zero as the reading on any of the 3 pairs then the stator is the fault... Rarely does the coil pack fault without impact or over heat but for the coil pack 0.08 - 0.10
let me know if you need clarification on testing ... Good luck!

You say it's flooding - is fuel coming out the overflows? If so, you might need to replace the needle and seat, but based on the age of the bike, I wouldn't think you would have to do that yet. Even with a bike that is raced, you can get many, many years on the needle without having to replace it - unless something damaged it. Inspect the needle and seat closely for nicks or imbedded **** in the sealing area. Also - I assume you set the float properly. This is an important step. Personally - I think the factory setting is too high - since about 2001 I have set the float 2MM lower than recommended. Otherwise you will have fuel pouring from the overflows on the faces of jumps or in the whoops.

If the engine is "flooding" - it could be down on compression which will make it run rich. Or you might just have to re-jet but I would only re-jet if the engine is fresh. You can also try running a B8ES pluf - it's a step hotte than stock and what I ran. Keep in mind that the ring in a 125 doesn't last long at all. There's only one ring. I would replace the ring before each race when I was running 125s - this happened every week during the season. 2-3 ring replacements per piston, 4-6 piston replacements per cylinder.

If you provide more info, I can give you a better answer on your exact problem - I don't know if I really know exactly what the problem is.

Scott

1) Is the choke stuck on? Solution: spray carb with WD40 and make sure it moves freely when you pull the choke on and off.
2) are you using the correct 2T oil? It may be that it is pumping too much oil through. TIP: Take out plug and look at colour. if it is brown/tan it is ok. if it is white then there is not enough fuel going in. if it is black and sooty then there is too much fuel (choke stuck on) if it is black and oily wet there is too much oil (adjust the oil pump as per handbook)
3) Could be ready for a decoke. How many miles has it done? Solution: REDEX teaspoon down spark plug hole, turn engine on kickstart with ignition turned OFF. Wait a few mins and start up bike as usual,a few revs should chuck out loads of smoke and clear its guts out.

JYACEO5C6YA003794 is not a valid VIN. However, JYACE05C6YA003794 is valid. The letter "O" is never used in a VIN. Below is the info requested. :-)

There are a lot of tiny fuel and air passageways in the carburetor that must be kept clean it order for your scooter to run right. Carefully, take the carburetor apart. This can be relative easy. The carb has tiny passages that can get gummed up. Your bike will not run correctly if the carburetor isn't completely clean, so take your time. I use a gallon container of carb dip (you can get a gallon at your local auto supply store).
First, remove all of the rubber and gaskets or they will get damaged. After a 20 minute soaking in carb dip, I blow out the carb with compressed air. You have to get all the jets and the passageways clean. Be sure the jets are clear, especially the starter jet. Sometimes carb cleaner won't clear out these tiny jets. Use a guitar or a piano string, a strand of copper electrical wire, or a tiny drill bit pin vise. Be sure not to increase the size of the hole in the starter jet or you'll change the tuning. Carefully reassemble everything, checking for cracks in the rubber carb boots and the gaskets. Replace them if they are old and cracked. Be sure and remove all rubber and gasket material first or they could get ruined. Spray carb cleaner also works if you're diligent.
If you have an electric choke, check it to make sure it works. Check the resistance between the wires - you should see around 10 ohms or less. Measure the length of the choke assembly. Remove the choke from the carb and plug the wires into a 12V source for 15 minutes. The choke body should be warm. Measure the length again - it should increase by around 1/8".
Next, consider whether your exhaust pipe is clogged. This is especially a problem with older two stroke scooters. The unburned fuel/oil mixture builds up in the exhaust pipe along with carbon over time. If the exhaust pipe is clogged, your scooter will run terribly or not at all. It can be difficult to tell if the exhaust pipe is clogged. The easiest way to tell is to remove it and try starting your scooter. It will be a bit loud - two strokes will sound like a chain saw. If it runs with the exhaust pipe off, you know that is the problem.
put a meter on the kill switch to see if you get voltage across it and check the magneto i would think that the contacts have gone rusty clean them with some fine sandpaper
also if the bike has been standing for a long time(six months or more) then replace the fuel because when its old it loses some flamabilty

hope this helps

John

Hi and welcome to FixYa, I am Kelly, Cylinder nuts= 22 ft-lbs / 264 inch lbs
Head nuts= 20 ft-lbs / 240 inch lbs If you had to change any crankcase studs the stud torque is 9.4 ft-lbs. / 112.8 inch lbs Thanks for choosing FixYa, Kelly

best to remove them

ATF is normally about 12 weight. You can use it if that weight works for you. I'll let someone else handle the how much part of your question.

I don't have the factory manual for the 83, but if the bolts are M8 x 1.25, the torque specs are 30NM. The oldest YZ book I have goes to 96, I checked for 96 to present is all the same. That is the standard torque for a fastener that size. Good luck!

It may be pop riveted, I know on the WR the plastic guard is fitted in Australia, not Japan, and they use what is called a rivnut, which is like a rivet but leaves a thread to screw into.
So if it looks like a pop rivet, it may be.

On a MX race bike like that you really don't check them just replace the oil regularly - every 2-3 hours ride time would be OK but if you can afford it then more often the better
Just double check with your local Yamaha shop for exact amount to refill back in to be certain is correct amaount but it will be approx 650mL

This is a highly ill - eagle act to do. In the old days we would put an electric drill on the drive cable, but now they make them tamper proof so they only go one way. The bezels are crimped on so you can't get inside them. I expect modern one may be electronic. How will your insurance company know what mileage you have done? I have never known an insurance cancel or fine due to mileage. You should have just disconnected it when you got close to the limit. Buy a used one and use them for 6 months in turns. There are two or three here 23K and one with 36k https://www.google.com/search?q=2002+yamaha+sr125+speedometer ..

Not mentioned in the Service manual http://www.badrad600.com/Yamaha_Radian_Factory_Service_Manual_OCR.pdf https://www.google.com/search?q=1986+Yamaha+YX600+Radian+remove+USA+speed+restriction Something like this?

Removing 95bhp restriction ' Yamaha Star Cycle V-Max ...

vmaxforum.net https://www.vmaxforum.net > threads > removing-95bh... Jan 14, 2013 - Air jets could easily become blocked. Step 3: Removing the speed restriction. On the back of the speedo-needle a disc with two different . ..

Check the diagrams here https://www.google.com/search?q=yamaha+sega+81+firing+order ..

Question edited for a lot more clarity, add maker. Question moved to Yamaha Motorcycle. Unlikely to be a carburetor problem as this appears to be fuel injected! https://www.google.com/search?q=Yamaha+Mio+125+MX+no+start ..

Make sure the fuel is getting to the valve and passing through it. Possible blockage in fuel line or in the tank.

It isn't called a Magneto, that was for really old bikes. It is a 'stator'. Service manual https://drive.google.com/drive/folders/1OFbBW2YhLpL1-Xbsw9vexi84Y7aXGTdG Parts List https://www.cmsnl.com/yamaha-rt100-1990-l-usa_model9624/partslist/ https://www.google.com/search?q=1990+yamaha+rt100+wiring+diagram ..

First make sure that the new battery has been fully charged and is not defective. Next make sure that the proper voltage is reaching the started. You may have a bad post connection or loose connection at the starter. Try jumping you battery with another known good battery.

Above the master cylinder on each brake.