1998 YZ 125 quit on me!! Please Help!!!!

Joined
Mar 25, 2001
Messages
262
Likes
0
#1
I bought the bike in March of this year and it was completely stock upon purchase with the exception of a new piston and ring. Shortly after purchse I installed an FMF Fatty pipe and FMF Shorty Silencer, FMF Power Reeds. After installing these it started running rich and bogging down low but made huge improvements on top. I switched the pilot jet from a STD #45 down to a #40 and moved the neddle clip from the middle position to the 2nd from the top position.

Yseterday was the first ride with the new carb setup and it ran awesome for the first trip out on the track. Our second trip out I was play racing with my brother-in-law and we were pushing it pretty hard and on the second lap when I was going over a big up hill double I gave it a little panic rev to keep the front end up it kind of sputtered while in the air. I took it easy for the next few sections and then it died while going around a turn to a downhill but when I rolled down the hill it fired back up and then just kept cutting in and out till I made it back to the parking lot. Once there I could not restart it.

I cleaned the filter on Saturday for the first time since purchasing a new one a month ago in preperation for our ride on Sunday. I was pretty sparse with the filter oil when I put it on the first time so there was a lot of loose dirt. After taking the carb off there was quite a bit of dirt in the air boot and on the air box side of the carb. So I removed all the jets and used a whole can of carb cleaner and after reassembeling everything it still would not start.

I started to get woried that I had leaned the jetting out too much and fried the piston so I took the cylinder head off and there are no grooves in the cylinder walls or pits on the roof of the head. The only thing I saw weird was there is a little blow by on the front side of the cylinder and with as much riding we have put in this summer I am probably due for at least a new ring and it must have just recently started because it wiped off with no effort what so ever.

So, what do you guys think?
Do I need to give the carb another cleaning?
Do I go ahead and order a new ring and see if that helps?
Or, (Last resort) let a local dealer mess with it and pay through the nose to trouble shoot it for me?

I was planning on sending the motor to Eric Gorr this winter and having a big bore kit done but with DirtWeek just around the corner I can't aford to do both and I would hate to put a new piston and ring on to only get a few rides in before I spend the big bucks and have Eric do his magic to it this winter.

Thanks for the help in Advance!!
 
Last edited:
Joined
Apr 2, 2001
Messages
66
Likes
0
#2
[sounds like you fried your top-end and seized it, did you ever think of breaking it in whene the piston and ring was brand new, that the most critical part of a new op-end is breaking it in, you also might have leaned the jetting out too much i would have just left it on the 3rd clip
 
Joined
Dec 10, 2000
Messages
1,490
Likes
1
#3
Did you try a new plug?:think

If you seized the top-end, there would be obvious marks on the piston. The popping and sputtering are symptoms of a fouled plug. I'll bet it will fire right up if you change the plug.
 
Joined
Mar 25, 2001
Messages
262
Likes
0
#4
Dah!!!

The top end was new 6 months ago MoToMaNYz125 so I doubt I would just now be seing the effects of improper break in procedures.

Yeah I tried a new plug spanky!!!

Thanks anyways guys.
 
Joined
Dec 10, 2000
Messages
1,490
Likes
1
#5
It sounds like your problem is ignition related to me. If you tried a new plug, then you need to start troubleshooting the ignition. You should check all the electrical connections as well.
 
Joined
Mar 15, 2001
Messages
212
Likes
0
#6
It doesnt sound like you seized the top end. Did you check your reeds? It sounds like you may have a cracked reed... Is it getting gas? You may have dirt in the petcock too...
 

MikeT

Subscriber
Joined
Jan 17, 2001
Messages
4,108
Likes
8
#8
Maybe you somehow sheared the flywheel key... If you did the bike won't run at all.
 
Joined
Dec 10, 2000
Messages
1,490
Likes
1
#10
Originally posted by KC_BigDog_51
If I sheared the flywheel key I would not be getting spark. See above quote from earlier post.
This is not neccessarily true. You can still have spark, it just may not be timed correctly.

Let's start with the basics here. For an engine to run, you have to have fuel, air, compression, and a spark, preferably delivered at the correct time. These are all easy things to check. Once you know you have the basic ingredients, it is time to start delving deeper. Is the timing off, due to a sheared key or a faulty ignition box? Are the reeds cracked or broken, allowing the fuel-air mix to bounce back and forth through the carb, making it hopelessly rich? Did the float stick, flooding the engine? If you eliminate things one by one, you will find the problem, and be ripping up the track again before you know it.
 

MikeT

Subscriber
Joined
Jan 17, 2001
Messages
4,108
Likes
8
#11
Originally posted by KC_BigDog_51


If I sheared the flywheel key I would not be getting spark. See above quote from earlier post.
You beat me to it Spank. Yes you can still have a spark but at the wrong time. I'd take a closer look at the fly wheel key. It might only be partially sheared (offset a little) and that's enough.