Just another "my bike wont start" thread...

Brandon H.

Member
Mar 26, 2009
199
0
Yeah so I picked up a 2000 CR125 yesterday, ran great. Started up first kick. Brought it home, started it again to show my friend and it started just fine. I pull it out this morning (changed the tranny oil, and topped of the radiator and cleaned the filter). Started up just fine (I think 2 kicks). Not expecting much anyways since the seller said there is only like 5 hours or so left on the piston/ring.

I took it out for a ride 5 minute ride today in the orange groves, warmed it up first and it ran great. Very fast, lots of top end power. No weird noises, nothing but just running a little rich. I ride it home and shut it down. Come back out 2 hours later to ride again, and it wouldn't start. I have been through a lot of stuff, but I just can't figure it out. I need help on this one. So bear with me, because I am explaining it below.
-------------------------------------------------------
I changed the spark plug. When rested against the head you can see a nice blue spark, you can even hear it. So it has spark, and it looks strong.

I took the carb apart and cleaned it. It looked very clean but I wanted to rule that out so I cleaned it anyways.

It has vforce reeds. I took the reed block out and inspected the reeds, reeds look to be in good condition.

Other then that, I took a compression test, came out around 110-120psi... pretty low. But it ran fine 1 hour before, and the kicker felt the same compression wise.

Sooo as a last resort, I tired bump starting it, just to see if it starts and its not because of weak compression.. and still no start. Motor turns over just wont even atemp to start.

WHAT GIVES??
 
Last edited:

_JOE_

~SPONSOR~
May 10, 2007
4,697
3
Hmm, do you have gas coming out of the fuel line at the carb? Out the overflow if you tip the bike? Plug wet after kicking? Too much air filter oil?
 

Brandon H.

Member
Mar 26, 2009
199
0
_JOE_ said:
Hmm, do you have gas coming out of the fuel line at the carb? Out the overflow if you tip the bike? Plug wet after kicking? Too much air filter oil?

I forgot to mention that info. Yes there was fuel to the carb, and if tilted far it would come out the overflow.

The plug I bought was brand new, in the right heat range. I compared it to the old plug, and to rockymountainatvmc.com Same stock plug

The old plug when taken out was a little wet. I took the plug out and kicked a little and ate lunch (assuming it was flooded), poped a new plug in and no start.. I have no idea if the plug was wet or not on the new plug, I have the head off at the moment. I could smell fuel though.

And the airfilter was not heavily oiled. I did it the same was as our other bikes, and they always ran fine.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
It would probably start, by pulling it with a quad. 5 hours is about the total time that your new top end will last. Check your crank and replace the seals while you are in there. Vintage Bob
 

Brandon H.

Member
Mar 26, 2009
199
0
whenfoxforks-ruled said:
It would probably start, by pulling it with a quad. 5 hours is about the total time that your new top end will last. Check your crank and replace the seals while you are in there. Vintage Bob

So what your saying is that my compression is so low that its obvious why it wont start.

Question is, why did it start first kick the last 2 times when started??

How many hours is a top end job suppose to last? I thought it was 40 hours untill next piston/ring change? Are you saying its only 5 hours?? Im not racing btw, just a trail bike.
 

holeshot

Crazy Russian
LIFETIME SPONSOR
Jan 25, 2000
1,823
0
Maybe it's just badly flooded.

Turn the gas (petcock) off, turn the throttle wide open and kick (or bump) until you're blue.

Make sure to turn off the gas at the end of the riding day to prevent flooding.
 

Brandon H.

Member
Mar 26, 2009
199
0
I figure while I am going this far, time for a new piston and rings and gaskets. Cylinder looks to be in good shape, haven't measured it yet though. I believe its standard bore. I was wondering who makes this piston in the pictures I am about to post, is it a OEM piston or ProX or...??? Also this cylinder look in decent shape to yall?? Scratches seem to be minimal, and don't catch the my fingernail.
100_2160.jpg

100_2165.jpg

100_2167.jpg

100_2166.jpg

100_2165.jpg
 

jb_dallas

Member
Feb 17, 2009
498
0
I always had good luck with wiseco pistons in 2 strokes. Keep in mind that compression testers are not always accurate. I had a RM125 that read 90 psi (on my cheap compression tester) after a rebuild and ran like a bat out of hell. If you arent racing it, I would guess a rebuild would be good for 30-40 hours on average. Most manuals will suggest a rebuid for the 125s at around 10 hours, but they are assuming you are racing the bike, since that is what it was designed for. Those 125s are not ideal for the trail, I sold mine for that reason.
 

Brandon H.

Member
Mar 26, 2009
199
0
I have heard stories about people and Wiseco pistons. Some people love them, some don't. I ordered from RockyMountianATVMC.com . I bought a Pro-x piston kit, gasket kit, top bearing, fuel filter, fuel line and vent line, and other small stuff like that. I had it overnighted as well. Hopefully it will be here tomorrow, and hopefully it will start once complete. I know 125's aren't best for woods, but after riding it so far I think its a lot of fun, I should get use to it fairly quick... might go through some plugs though.
 

Patman

Pantless Wonder
LIFETIME SPONSOR
Dec 26, 1999
19,774
0
The JD Jetting kit (same as the 250) did wonders for helping get my son's '01 CR125 spot on. I actually like that bike so much I'm thinking about doing a full CRE125 type build on it to make it great in the woods.
 

Brandon H.

Member
Mar 26, 2009
199
0
Patman said:
The JD Jetting kit (same as the 250) did wonders for helping get my son's '01 CR125 spot on. I actually like that bike so much I'm thinking about doing a full CRE125 type build on it to make it great in the woods.

CRE125??? Care to explain??
 

Brandon H.

Member
Mar 26, 2009
199
0
Lets talk about pistons for a second. I know most Weisco pistons have instructions for drilling exhaust bridge ports. I ordered a Pro-X piston, made by the same place OEM pistons are made, ART. I want to drill exhaust bridge holes in my piston to help cool and lube the exhaust bridge.. but is it a good idea on these pistons?? I don't think these pistons come with instructions on this (but I could be wrong).

How big of a drill bit would I use? I noticed the bridge isn't very thick at all. How high on the piston.

Could this hurt anything?

How would I debur the hole properly?
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
I would take that cylinder to a dirtbike professional and have them check the bore, and straighten out the cross hatch at least. It looks like some kid went at it with a drill. Do not ask how I know. Fit it with the wiseco for sure. Get a manual for it and actually read it. Take notes. Get an hour meter. You have a plated cylinder. And I would recommend 40 hours on a 125 on planet bizarro world. Running long on top ends will oval the bore. The top end life is short, what did you expect for a 125 2 stroke race engine? My 97 CR 250 ring life is 5 to 7 hours, read the book. What some guy was able to get, and stories of 100 hours, what ever. I do not race as opposed to I only race up and down the fire roads? When you wonder why it runs funny? When you think you have gotten faster? Your bike needs service, way more than riding time. Its not an XR or PW. That top end should push over 200 psi, on an accurate gauge. Check it fresh, check it once a week, when it drops off, it needs rings. Vintage Bob
 

Brandon H.

Member
Mar 26, 2009
199
0
sr5bidder said:
Brandon
did you happen to see the exhuast bridge holes in the piston you removed?

No, there are no exhaust bridge holes in the piston I just removed.
 

Brandon H.

Member
Mar 26, 2009
199
0
2strokerfun said:
ART are usually cast pistons. I've never drilled exhaust bridge oil holes in one.
They are for sure cast pistons, I know that. Maybe I will just go without the holes, maybe its just for forged pistons.
 

Brandon H.

Member
Mar 26, 2009
199
0
Bodge said:
You didnt leave a rag in the air boot while cleaning the airfilter did you?

No sir, thought that for a second too. I pulled it out, 100% sure.
 

jb_dallas

Member
Feb 17, 2009
498
0
200 psi is ALOT of compression for a 125. Most sources would suggest 150-160 is very healthy. Search the internet....most 250s wont push over 200 psi without modifications.

I know a guy personally that has over 100 hours on a KTM 250 SX. The bike has never been on a track, only trails. The bike has also been maintained regularly and not abused. 30-40 hours on a 125 is not uncommon. Longevity has more to do with how the bike is maintained and how it is ridden than the actual number of hours. A good example is the CRF450X...the manual suggests a new piston every 15 hours. There are many of these bikes on the trail with 50,60,70+ hours and no problems...as long as the valves are kept in tolerance. The manuals all have those low service intervals because they want your money...its clever marketing.
 

Brandon H.

Member
Mar 26, 2009
199
0
Ok im getting really frustrated now.

For starters, how much fuel is suppose to be inside the the crankcase?? When I had the topend off, there was about 2-3oz of fuel sitting under the crank. I know there is suppose to be some, but is that too much?


I just put in a piston kit from Pro-X. Lubed the cylinder with premix, put it all together, compression feels better. New plug, carb cleaned, reeds checked. I still cant get the damn thing to fire. :bang: :bang:

I checked the spark again, there is plenty of it, nice blue zap. The bike has compression. Its not a whole crap load of compression, but then again I wonder if its just my mind because the kick starters on there are longer then most, hence more leverage and easier kicking (maybe).

I tried dipping the plug in fuel, and putting it back in the cylinder, no start still.

WTF!!!! :bang: :bang: :yell: I am not new to motors, and I am stumped.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
There is not supposed to be fuel in the crank cases, its extremely flooded. Stuck float, out of adjustment, or the float valve that should be replaced yearly? Turn it upside down, or draw it out all that excess fuel. I do not believe I would poke holes in a piston, unless the directions say to, wiseco does. If you ever get the jetting/carb sorted out, replace the silencer packing. What was the ring gap set to? What was the skirt clearance at? What was the bridge clearance set at? Vintage Bob
 
Top Bottom