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Author Topic: yz 125 bogging low end  (Read 5741 times)

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Offline MOMSMX47

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yz 125 bogging low end
« on: July 06, 2013, 05:20:48 PM »
Just picked up an 05 YZ 125    has an FMF pipe and shorty silencer on it   kid says it was not rejetted when he installed them  says top end was done beginning of this season and he was running 32:1 for the mix rate.

now the problem

i get compression about halfway through the stroke of the kickstart,   when running it runs very rough  and stalls easily   but the biggest issue is in 1st  and low 2nd gear it is bogging heavily   almost like the choke is on    but once i get high into 2nd and its really revved out high  it runs as it should.


Crank Seals?
Reeds?
Mix Rate/ Bad gas?
top end?
jetting?
idle screw?


what do you guys think. Trying to get this running for tuesday in top shape   alreday did a new plug so its not that
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline _X_

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yz 125 bogging low end
« Reply #1 on: July 06, 2013, 07:56:36 PM »
first try turning out the air screw on the carb to clean up the low end (quarter turn at a time). check to see if the main jet is not sitting in the drain plug before you get some more involved responses.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline MOMSMX47

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yz 125 bogging low end
« Reply #2 on: July 07, 2013, 01:12:14 AM »
ill play with that tomorrow  though I will say that  I had two techs from my work ride it today   and both said  that is normal for a 125 to bog down like that low in the low gears and that you just have to feather the clutch.    I dont remember doing that with my 2003 CR   and certainly dont have to with my 2013 YZ250    but two of them did say it.....any fact to this?
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline Stusmoke

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yz 125 bogging low end
« Reply #3 on: July 07, 2013, 08:24:16 AM »
ill play with that tomorrow  though I will say that  I had two techs from my work ride it today   and both said  that is normal for a 125 to bog down like that low in the low gears and that you just have to feather the clutch.    I dont remember doing that with my 2003 CR   and certainly dont have to with my 2013 YZ250    but two of them did say it.....any fact to this?

If you mean bog as in BUUUURRRRRRRRMMMMPPP like its jetting is rich, then those two techies are F*(king retarded and should have their licenses revoked. It is simply, not, true. If its bogging like you say it is, theres a problem and its not that the engine doesn't have cams like most 4 stonk techies these days are very quick to claim. 125s always have been and always will be very slow down low. Its only until about 8 or 9 grand (roughly) that they start making any decent, raceable power.

Now that my little rant is over, onto the problem(s). First off: the kickstarting only getting compression halfway through the stroke. Have you tried just going through the first half then releasing it and trying again? Try to find top dead centre.

Second problem: You say it runs rough and stalls easily. I would start by throwing out the gas thats in the tank and mixing some good, fresh gas with good oil @ 32:1 like the PO was apparently doing. Give that a try. Also, google around and see if you can find the manufacturers recommended mix ratio. This includes what octane rating they recommend. Then try and find the same for the idle air screw. Considering that its running an FMF pipe and shorty silencer go a little richer to be on the safe side. Oh and for future reference, I would recommend ALWAYS throwing out the gas, coolant and oil that came with the machine. Unless its your dads old bike or your brothers or something and you can be dead certain that everything is fine.

Thats a good starting point before doing anything too rash. Good luck, and post a picture of the new sparkplug after about 2 minutes of idling and riding in the boggy part of the revs.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline TMKIWI

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yz 125 bogging low end
« Reply #4 on: July 07, 2013, 09:27:27 AM »
Pull the carb, strip and clean.
Check with the fmf website what jets they recomend and compare with what you have.
Pull the reed cage and check for chips. Not the potato kind.
Fix any of the above issues.
Full with fresh gas and ride.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline mj4trax

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yz 125 bogging low end
« Reply #5 on: July 09, 2013, 05:05:48 PM »
good avice so far on this thread.

One thing I can add as your problem sounds like one I had on my '01 yz125 is that you may have a fuel leak past your choke plunger.  On that Mikuni carb, the choke isn't really a choke as much as an additonal passage to dump extra fuel in the motor.  Made my jetting really erratic on the bottom, didn't seem to affect higher revs much.   

It was really hard to narrow this down, and when I pulled it out, there really wasn't a ton of wear...  I just randomly tried one out of another bike and problem was fixed.  Less than $10 for a new part. 
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline MOMSMX47

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yz 125 bogging low end
« Reply #6 on: July 12, 2013, 04:45:27 PM »
Thank you for the help   we just ordered a set of reeds, and new jets   going to try that this week
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline MOMSMX47

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yz 125 bogging low end
« Reply #7 on: July 12, 2013, 04:50:38 PM »
ill play with that tomorrow  though I will say that  I had two techs from my work ride it today   and both said  that is normal for a 125 to bog down like that low in the low gears and that you just have to feather the clutch.    I dont remember doing that with my 2003 CR   and certainly dont have to with my 2013 YZ250    but two of them did say it.....any fact to this?

If you mean bog as in BUUUURRRRRRRRMMMMPPP like its jetting is rich, then those two techies are F*(king retarded and should have their licenses revoked. It is simply, not, true. If its bogging like you say it is, theres a problem and its not that the engine doesn't have cams like most 4 stonk techies these days are very quick to claim. 125s always have been and always will be very slow down low. Its only until about 8 or 9 grand (roughly) that they start making any decent, raceable power.

Now that my little rant is over, onto the problem(s). First off: the kickstarting only getting compression halfway through the stroke. Have you tried just going through the first half then releasing it and trying again? Try to find top dead centre.

Second problem: You say it runs rough and stalls easily. I would start by throwing out the gas thats in the tank and mixing some good, fresh gas with good oil @ 32:1 like the PO was apparently doing. Give that a try. Also, google around and see if you can find the manufacturers recommended mix ratio. This includes what octane rating they recommend. Then try and find the same for the idle air screw. Considering that its running an FMF pipe and shorty silencer go a little richer to be on the safe side. Oh and for future reference, I would recommend ALWAYS throwing out the gas, coolant and oil that came with the machine. Unless its your dads old bike or your brothers or something and you can be dead certain that everything is fine.

Thats a good starting point before doing anything too rash. Good luck, and post a picture of the new sparkplug after about 2 minutes of idling and riding in the boggy part of the revs.

the techs arent exactly the best   ill admit.   The gas is now new  and it still did that,  the top dead center...ill get back to you on that  didnt try that yet and the bikes out west right now. 
« Last Edit: December 31, 1969, 04:00:00 PM by ' »

Offline Stusmoke

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yz 125 bogging low end
« Reply #8 on: July 12, 2013, 10:25:01 PM »
Finding TDC is usually a four stroke method. But you need it on a 250 as well. correctly jetted 125s are unbelievably easy to start they just fire right up.

This is most likely a rich problem and should be fixed by some slightly leaner jets. What mix do you run? In a 125, I recommend 20:1 or 25:1. Keeps that bottom end lubed up well. Actually thats a mix I recommend for just about any two stroke.

When you've got your carby apart, do what TMKIWI suggested and run through it with some carby cleaner. Check all the parts for wear particularly around the float mechanism. Check and adjust throttle cable too.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »