What Is Bog?? Jetting Help Rm 125

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Jul 24, 2003
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#1
I have a 1997 rm 125 and I do not know what to call what it is doing?? When I try and go full throttle it slows makes a deep drowning kind of sound and 2 seconds later I take off barely holding on. I have tried to jet it, I have a 160 main and a 42 slow jet. I have the needle clip on the most leaniest setting. But I still foul plugs. I have tried to Mess with the air screw turning it out 2 and a half turns and then back and it still does it. WHAT AM I DOING WRONG???? I just want to ride my bike and I feel like I am not able to use it to its full compacity. Now when I just slowly turn my throttle it goes fine, but say Im in sand and really hit it It dies and Im stuck. And help or ideas would be great. I am starting to think that suzuki is not a good bike.
 
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#2
I'm no expert, but I'll give you my 2c. The best way to describe a lean bog, is if your riding with your fuel off accidentaly, and its kinda runinning "ring-ey" and snappy and when you stab it, it may lurch then go buuuwhhhhaaaaa. Running really rich will make your plugs BLACK and foul when your warming it up, and it will be surgy, hesistent, and slower, and not really rev to as high a RPM. Moving the needle doesnt effect it at Wide open, but basiaclly from like everything in the middle of your throotle movement. Umm theres tons of signs of going rich, the engine will feel more like a 4-stroke than the snappy 125 that it is, it will sound blubbery, and make a kinda, well studdering sound. At wide open its hard to tell that though. What kind of oil are you burning, somtimes gummy high temp oils that are for serious racing will cause the bike to hesistate for a second. Also the exsaust, exspecially at wide open, if you can fly down a road on a calm evening then go back and smell the exsaust, if it smells like theres gas fumes mixed with the oil, it's rich. Hope this helps you diagnose it, as for not likeing the yellow bike, they're all so similar, some people get brand lowalty in their blood and for what? From what I opserve at the track, lots of the best 125A guys, are on RM125s, they make good bikes. Ohh yeah I forgot, spooge, the black stuff that drips out the silencer is a good sign of a rich carb, though a slightly rich carb may not spooge, but a clear nose can smell the gas fumes.
 

tedkxkdx

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#3
So go down in your main jet size. Move one size at a time so you don't go too lean first time out. Jets are way cheaper compared to a blown engine.
When you whack the throttle wide open quick it seems to not be able to burn all the gas and means it is rich. Your in Colorado and it is high there. I would think a 160 is too rich. You could go to the track and ask other rm guys what they run for their jetting. You may have to change some of the other carb parts too, like pilot, needle, to get the right jetting for a screaming bike. Remember what beefy dog said about when a bike is too lean it will seem very responsive and powerful, but don't be fooled, since it will blow your engine. The other carb parts are tested with different throttle settings, but the main jet is critical since you may be on that more than any other jet.
 
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#4
so is it bad if I have a too low slow jet??? I live at about 6000 ft elevation. My bike smokes like a chimney, I was told that a bike is suppose to smoke but I can turn the throttle and it fills up the garage. See when I go up a hill or anything where I turn the throttle too fast it blub blub blub blub and then gets going. But if I am in sand it just dies. It will cost 60.00 to get it jetted, but I don not want to pay if it does the same, and if I can do it myself. I have tried lowering my main jet, I still foul plugs. Someone also told me that with a 2 stroke you have to really keep it going in the powerband so that it does not feel up with gas, like not to just putt around in first gear. Oh yeah I use a 32:1 mix with yamalube.
 
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#6
Remember what beefy dog said about when a bike is too lean it will seem very responsive and powerful, but don't be fooled, since it will blow your engine.


I dissagree, in that if properly jetted, a two-stroke SHOULD be very responsive, and powerful. Usually, a lean condition will cause a loss of power, a "ringy" sound to the exhaust, and surging at a steady midrange throttle setting. A bog a WOT can also be a lean condition, in that the engine is asking for more fuel. And if you can't tell a difference while turning your air screw in & out, your pilot jet is probably either too large, or too small. AND.....a well jetted 2-stroke should have little or no spooge, if using a good quality premix oil, and providing that the bike is being ridden in similiar conditiond, ie temperature, altitude, humidity, etc.

Check out the link below for a VERY comprehensive, and easy to understand jetting lesson.

http://justkdx.dirtrider.net/carbtuning.html
 
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#7
Hey I have alot of spooge. I have it dripping from my exaust where the silencers meets it , also at the end of the silencer it just shoots out at times all over my rear fender. See I bought the bike used and it is in perfect condition, but I am leaning towards trying to get a 4 stroke maybe so that I do not have to worry about spark plug fouling.
 

tedkxkdx

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#8
You are at a high elevation, so most all of your jetting is probably rich. Don't be scared of taking on the jetting of your bike. Read the articles above and do it yourself. The jets are cheap and you will learn in the process of doing. $60 is way too much and may not even be correct at the end of the day.
Find some other riding buddies and ask them. The have probably gone through the same thing since they also live at 6k.
 
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#9
Thanks for the help I hope to tackle it on thanksgiving. See my problem started out that my bike would not Idle. If I was riding and went to put it in neutrel it would hesitate then just die. Well the last time it died a few miles away from the truck, boy was that a bad day. Anyways I started looking into what it would take to jet it, it did not seem like much. At the local track the mechanic said that he would get it like brand new, but I guess I am cheap and wanted to learn myself. I really like the articles about using white out and figuring out what is 1/8 1/4 1/2 and so on. I found that just by reading that that it seems lik between 1/2 and full throttle is when it is messing up. Now the site stated taht this would be because of the needle clip, and I have the needle on the leanest point, so maybe if I bring it down it may help, but I still feel like my main jet is rich. I just did not understand the formula for figuring attitude. It involved drawing a line from the attitude to the cc or something like that then he took that number and multiplied that to get an idea of the right jet. Any Idea how that works??