running rich

[dwcdds93]

I just bought a 95 yz 125. It starts very easily and idles well (with a little help from the throttle). When I give it hardly any gas, it sputters out and won't rev. It seems like it is flooding out. I have replaced the air filter, rebuilt the carb, checked the reeds, and replaced the spark plug. The plug is wet and oily after the bike runs for about a minute. Also, the exhaust is very cloudy at idle and during reving. I am unsure of the main jet in the carb. I believe it is stamped 200, but the manual says the factory setting is 360. Could this be the problem? Is it an ignition problem? Any help is appreciated.

PS: I am new to the forum and it seems pretty cool. Thanks for any help.

 

[sick 96 250]

that 200 on the main jet sounds crazy. I think you should be somewhere at 360 on the main, 53-55 on the pilot and 3rd clip on the needle with air screw 1.5 turns out, what number is your pilot jet? 200 sounds way off tho on the main. Also a lot depends on what kind of work is done to the bike and the elevation your running at. But try those settings i marked down for ya and see how it responds then. Good Luck

 

[dwcdds93]

Update-
Checked the ignition coil tonight with an Ohmmeter, everything checked out according to the manual. Checked spark, and had it when just kicking over the motor. Cleaned the terminals. Started it up, idled fine. Took it off choke, tried to move it past 1/4 throttle, loads up and runs fat. Won't rev up. If you hold the throttle open, it backfires into the airbox a small amount (can see flashes in the airbox), also flashes out the tail end of the silencer. Going to check the main jet tomorrow at the dealership to make sure it is the correct one (360 accrding the manual), but other than that, am stumped. Just seems to be runnin really fat. Lemme know if anyone has any other suggestions.

 

[mxmatthew]

my guess would be jetting. Sorry Im not good with jetting at all but I would start by changing the main jet, then maybe the clip position. Hope this helps!

 

[dwcdds93]

I have the main jet out again, it says 200. I didn't check the pilot jet yet, but I will. I am at the third clip position and 1.5 turns out on the air pilot screw. I am going to pick up a 360 jet tomarrow and try that.

 

[sick 96 250]

def put the 360 main in, or you could go a little lower on it if possible. You should pick a few of them just to make sure. (Different sizes) Check the pilot before you go get the main jet as the pilot may be way off also if the main was off that much. Good luck and keep us posted

 

[dwcdds93]

the pilot jet is 55, what the manual calls for. the new 360 jet works to almost solve the problem. it almost seems to run lean now at high throttle. it stumbles and runs rough. i adjusted the clip on the needle from 3rd to 2nd down, 4th down, and 5th down. it seemed to run the best on the 5th ring from the top. it was pretty cool outside when i was messing with it though. this could have something to do with the lean condition. i am going to pick up a few more jets to adjust it till it runs the best.

 

[shnalln]

If it runs best with the needle raised, it almost seems to me that you'd be fat on top seeing as how stock bikes are jetted at sea level and the 360 is the stock jet. I'm not sure where you are but would venture to bet that a 350 or 340 main would get you closer to where you want to be....?

 

[sick 96 250]

are you saying it was best when the clip was on the last notch towards the bottom of the needle. If thats the case, try going up on your pilot a few sizes. If you meant the very first clip from the top of the needle try a few sizes down on the pilot. As for the main, normally factory jetting tend to be rich so you could drop a few sizes on that more than likely. If its working the best when you keep changing the needle clip it is most likely your pilot is off now. The clip and the pilot accomodate for closed throttle to about half if i'm correct, the main is when your bike it opened up. Try a search on here someone who has the same problem. Like a said normally you can go down a little on the jetting from what is recommended since they are normally geared rich from stock settings, try a 52 pilot possibly and a 342-350 main. Keep us posted

 

[shnalln]

the pilot jet is 55, what the manual calls for. the new 360 jet works to almost solve the problem. it almost seems to run lean now at high throttle. it stumbles and runs rough. i adjusted the clip on the needle from 3rd to 2nd down, 4th down, and 5th down. it seemed to run the best on the 5th ring from the top. it was pretty cool outside when i was messing with it though. this could have something to do with the lean condition. i am going to pick up a few more jets to adjust it till it runs the best.

Actually I think that's a rich condition at full throttle rather than lean. What does plug look like? If there is a white spot on the plug then your probably lean somewhere, but my guess is, since you went back to stock jetting, (which is the best thing you could have done in this situation) that it's probably black and wet.
If full throttle is where you are seeing performance issues, then i'd adjust the main down first. But that's just me.
I'm not sure if you've had a chance to look at this, "HERE", but there is some really great info for tuning carbs...

 

[dwcdds93]

i tried to buy a 350 jet today to try that, but i could not find one anywhere (have to order it). i did buy a 370 though. i tried it and it seems to run pretty well. it revs pretty consistantly all the way through throttle, until about 3/4 to full throttle. The plug looks about half white and the other half is almost black. does this mean it is still lean? also, it seems to run pretty good at low rpms with the stock 55 pilot jet. should i still attempt to change that as well now, and should i still try the 350 main jet? thanks for the help

 

[cactusreid]

The bike may have spun the flywheel/broke woodruff key on the crank. My son's yz 80 did this a while back with similar symptoms. Pull your flywheel and check the key etc. A freshly bought bike that doesn't run right-has all the signs of a not normal tuning problem. I bet the previous owner played around with the jets enough to make it run -just so you would buy it.

 

[dwcdds93]

i got it for really cheap, so that isn't really an issue. the previous owner did say that he had put a new flywheel on, but didn't elaborate on why. could this have something to do with you are talking about?

 

[BJH]

check timing? Check float level?

 

[shnalln]

If your plug is half white you've got a problem I'd say and something is making you run lean. Where at in the world are you, at or above see level? What's your elevation? Are you running stock pipes etc, or aftermarket?
If your above sea level and stock jetting is turning your plug white something is going on. Maybe try cleaning your carb real good and blowing everthing out to make sure that something is not plugged up.

 

[sick 96 250]

the blurp on the top end from 3/4 to full throttle is your main jet it sounds like. Probably have to come down in size on it. if the plug is turning white that is a lean condition it sounds like. As mentioned we need to know where you are above sea level and so on. Try a good cleaning of the carb. Take everything apart, (jets, floats, air screw, choke knob, etc) and just clean it really good getting everything in the holes and passed through the jets so nothing is clogging it up, reassemble and try it out. Make sure your float levels are correct also

 

[dwcdds93]

i already disassembled and cleaned the carb with carb cleaner and blew out all passages. the float is set to factory setting. i am located in Indianapolis IN. not sure what the elevation is. also, i have been asking service people questions and one said it could possibly be the main bearing seal around the crankshaft and the another said it sounds electrical, like the coil is not functioning correctly under load. i am going to check the stator coil tonight and have the coil tested under load tomarrow. is there a way to check the bearing seal without replacing it? the dealership didn't have any in-stock, and i didn't want to order and change it if it isn't bad.

 

[sick 96 250]

i have been asking service people questions and one said it could possibly be the main bearing seal around the crankshaft and the another said it sounds electrical, like the coil is not functioning correctly under load.

If i'm correct, if you had a crankshaft bearing go that would make you bike run rich and cause a wet oily plug foul. That happened on my bike. Not to sure about the coil problem. Maybe an airleak somewhere could be a problem but i do not know. Just sounds more like a jetting issue since the bike starts easily. When my rh crank bearing went my bike was hard to start untill it was fixed. Keep us posted

 

[shnalln]

Just out of curosity, have you checked the gasket on the reed valve?

FYI, Indianapolis International Airport is 797 ft ASL. Stock jetting should NOT be too lean.

 

[dwcdds93]

Update: the stator coil checked out okay, we rebuilt the top-end and cleaned the exhaust valve and the bike still ran the same. we had the flywheel cover off and noticed that the woodruff key was in the bottom of the housing. we replaced it and the bike started to run better. now it starts and idles good like before, revs up some, but not on the top end. it no longer stumbles/pops/misses like it did before, however, it does not want to rev up like it should, and seems to be very weak. the plug looked the same as before, half black and half white. i bought the crankshaft seals and we are going to try those tomarrow. does anyone have any further ideas on what it could be or where to go next?

 

[sick 96 250]

any updates on situation?