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125 sounds different from others

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Hello,

i m just wondering why my sx 125 makes such a different noise when i go on the gas in the air like she s gonna dieing. i watched the videos from barcia and decotis and their 125 s sound like they have a rev limiter. does somebody know it?

thanks

thegoooonrider

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They don't have a rev limiter. Can you describe the sound better or post a video. Is it cutting out or pinging? What year is your bike? What size jets are in it? How does the plug look?

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honestly those bikes are 125s but imo....they do not run like one they new a hell lot higher running rpms, they all have rev limiters...if they didnt then the thing would rev like no other. a rev limiter is just a the revving that thing in your cdi that starts cutting the spark off so your motor doesnt rev any higher.....say you had your bike in 1st gear you could tie it up to something and pull it so where the thing just revs past its rev limit.... but when you are revving that high theres a chance your piston will over heater, or your connecting rod might break because it cant with stand the abuse... the factory teams have freshly packed exhaust jetted absoluely perfect and they are running on race fuel with the highest grade oil possible also they do have polished and hardend gears and have titainium and fordge everything

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If you put the bike on a stand so the rear tire is in the air, and rev it in whatever gear you are hitting that jump in does it make the same sound? The exhaust noise will be different with no load on the engine. Plus the rear tire acts like a giant flywheel when not on the ground.

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ok, i made a video in which you can hear it

video

IDK, does it sound much different then mine?

http://www.tye1138.com/stuff/vetuphillgood.mov

You've got the throttle pinned when your in the air, your hitting the max RPM for some reason. IDK if you're trying to do that or not...

You are clearly WAY in the wrong gear, if your in 2nd, be in 3rd or 4th over that same jump. My video above is 4th gear, so you can see how much more speed I've got and how much lower the RPM is.

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honestly those bikes are 125s but imo....they do not run like one they new a hell lot higher running rpms, they all have rev limiters...if they didnt then the thing would rev like no other. a rev limiter is just a the revving that thing in your cdi that starts cutting the spark off so your motor doesnt rev any higher.....say you had your bike in 1st gear you could tie it up to something and pull it so where the thing just revs past its rev limit.... but when you are revving that high theres a chance your piston will over heater, or your connecting rod might break because it cant with stand the abuse... the factory teams have freshly packed exhaust jetted absoluely perfect and they are running on race fuel with the highest grade oil possible also they do have polished and hardend gears and have titainium and fordge everything
Two-strokes don't have hard limiters like four-strokes. Four-stroke limiters cut the spark, because of the real danger of floating a valve and destroying the engine.

Two-strokes have what is called a soft limiter. All they do is progressively retard the ignition timing beyond a certain rpm level. And they are far more limited by their breathing ability than by the ignition.

Factory bikes sound very different than production bikes, because they are in a very different state of tune. Different porting specs, different ignition curves, much higher compression and much better fuel than the crap that comes out of pumps, etc.

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@tye1138:

if i rev it just for a moment like you, it sounds same, but if i stay on the gas the rpm goes down.

i cant try it on a stand, because my bike is disassembled at the moment, but i know that if i rev in neutral, the rpm stays high.

i just want that the rpm doesnt go down so hard under load.

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After watching your vid, it sounds like you have a slight bog when you land? Raise the float slightly, it should solve the problem.

If you can't cure it with the float, then you'll want to install a T-vent system in the carb vent lines.

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The carb has a vent (some have two) from the float bowl that goes straight down. On hard landings fuel can slosh into the vent hose and block the air flow, causing a brief pressure drop in the float bowl that interrupts the fuel flow for a second. A T vent is nothing but cutting a T into the vent hose close to where it connects to the float bowl and running a second hose up into the air box. This helps to prevent the loss of air flow through the vent during landings.

Raise the float height a little first, that should fix your problem.

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if i rev it just for a moment like you, it sounds same, but if i stay on the gas the rpm goes down.

Got ya, I thought you had killed the throttle and thats why the RPM's went down.

This helps to prevent the loss of air flow through the vent during landings.

Raise the float height a little first, that should fix your problem.

Yep, gotta keep those hoses clean and I agree the float could be messed up as well. It might have been a re-assembly issue from a while ago and just never came to light until now as the spring does wear a tiny bit over time.

If this happens during jumps only, then yes this makes sense. But if it happens all the time, I might be looking at ignition. I've had lots of ignition problems that act that way.

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ok thanks, i will replace the tubes and put in a t vent when i put my bike together again.

one question, where did you noticed the bog in the video? i can't hear something strange when i landed.

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one question, where did you noticed the bog in the video? i can't hear something strange when i landed.

When you were in the air and the motor all of a sudden stopped revving. When you landed and the motor was silent for a little bit, that all sounded very strange to me.

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