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Hey guys, I have a stupid noob question about my jetting. I'm kind of stressed out that when I get my bike running, I'm just going to blow it up again due to jetting, because I'm still trying to tackle the basic concept of it. My main question is how bad is it to run the bike with the jetting not perfect?  Can it actually cause damage, or will it just run like crap? I'm sure this probably has a simple answer and most people will pass this by but honestly I don't know.  Thank you for your input and time!!   Also my bike is a Kawasaki kx 125.

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Too rich is fine.  Won't cause any damage.  Too lean can destroy the entire motor.  Eat the pistons, and/or destroy crank bearings.  So you want to be careful how you jet the thing.  

Now that I have your attention, too lean won't instantly destroy the motor and it is dependent on a few factors.  However, run it too hard and too long too lean and the things I mentioned above will occur.

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41 minutes ago, CDNSXV said:

Too rich is fine.  Won't cause any damage.  Too lean can destroy the entire motor.  Eat the pistons, and/or destroy crank bearings.  So you want to be careful how you jet the thing.  

Now that I have your attention, too lean won't instantly destroy the motor and it is dependent on a few factors.  However, run it too hard and too long too lean and the things I mentioned above will occur.

So is rich to much gas not enough air? And the way to tell is if it boggs when you hit the gas and sputters with a lot off smoke? What are the warning signs of lean? Also my main concern is that it will be lean when I have to break in a new top end (when I can pay for it)  because I don't think I will be able to Jett and break it in at the same time. Thank you for your time.

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Also I think it was running lean for a wile before I even really new anything about dirt bikes this is my first bike. So I cold seized the thing, I think because of not letting it warm up before riding hard and when I tore it apart the piston had some damage due to running lean, but the rod bearing has no play. So I'm not really into tearing the bottom end apart if its not nessesary. Do you think if the rod dosn't  have any play that it will be fine?

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"Bogging" can be caused by being too rich or too lean.  As long as you have a fair amount of oil mixed in with the gas, say 50 parts gas to 1 part oil you should be able to start it up and get it running correctly with out hurting the motor.  The easiest thing to do is look up the original jetting specs and put the carb back to stock with the idle speed screw 2 1/2 turns out from the all the way in position and the air screw 1 1/4 turns out from all the way in.  This should give you a safe platform to start with.  It probably won't run as well as you would like with these settings.

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2 hours ago, GlennRay said:

"Bogging" can be caused by being too rich or too lean.  As long as you have a fair amount of oil mixed in with the gas, say 50 parts gas to 1 part oil you should be able to start it up and get it running correctly with out hurting the motor.  The easiest thing to do is look up the original jetting specs and put the carb back to stock with the idle speed screw 2 1/2 turns out from the all the way in position and the air screw 1 1/4 turns out from all the way in.  This should give you a safe platform to start with.  It probably won't run as well as you would like with these settings.

 

So, I should just go back to stock jetting and go from there after breaking the new top end? I think your supposed to run more oil anyways when breaking in a new top end. I was running 32:1 so do you think 50:1 would be good to keep it on the rich side?

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2 minutes ago, Jack wagon said:

 

So, I should just go back to stock jetting and go from there after breaking the new top end? I think your supposed to run more oil anyways when breaking in a new top end. I was running 32:1 so do you think 50:1 would be good to keep it on the rich side?

When you put more oil into the gas you are actually making the engine run leaner.  It gets less combustible gas to burn on each intake stroke.  I have never run less than 50:1 on any two stroke engine that I ever owned, MX bike or Trials Bike.  You should follow the vendors guidelines however.  As far as the carb settings go, I would go back to factory settings to start the berakin process.

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2 minutes ago, GlennRay said:

When you put more oil into the gas you are actually making the engine run leaner.  It gets less combustible gas to burn on each intake stroke.  I have never run less than 50:1 on any two stroke engine that I ever owned, MX bike or Trials Bike.  You should follow the vendors guidelines however.  As far as the carb settings go, I would go back to factory settings to start the berakin process.

Ok , thanks!!

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If it were my engine I would do the following with the stock carb settings in place:

1. Drain whatever pre-mix is in the gas tank.

2. Put 1 gallon of 50:1 pre-mix gasoline and whatever two stroke oil you like.

3. Start the bike, fiddle with the carb until it idles.

4. Let it idle for 3 minutes.

5. Pull the spark plug and see what it looks like.  Light tan to brown means that you pilot jet/throttle slide cutaway settings are working mostly correctly

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Then put the spark plug back in and start the engine again.  This time pull the throttle up to 1/2 for 3 minutes.  Kill the engine with the kill switch and pull the spark plug again.  If it is still light tam to brown then the needle jet and needle are working mostly correctly.  If the spark plug is black you need to lower the needle or reduce the needle jet in size.  If the spark plug is white you need to raise the needle or increase the needle jet in size.

Put the spark plug back in and start the engine again.  Peg the throttle for three minutes.  Remove the spark plug and look at again.  This time white means lean on the main jet, tan or brown means pretty correct on the main jet, black means rich on the main jet.

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36 minutes ago, GlennRay said:

Then put the spark plug back in and start the engine again.  This time pull the throttle up to 1/2 for 3 minutes.  Kill the engine with the kill switch and pull the spark plug again.  If it is still light tam to brown then the needle jet and needle are working mostly correctly.  If the spark plug is black you need to lower the needle or reduce the needle jet in size.  If the spark plug is white you need to raise the needle or increase the needle jet in size.

Put the spark plug back in and start the engine again.  Peg the throttle for three minutes.  Remove the spark plug and look at again.  This time white means lean on the main jet, tan or brown means pretty correct on the main jet, black means rich on the main jet.

The motor must 100% be run under load.  Simply pegging the throttle with the bike in neutral won't tell you anything.  Three minutes of WFO throttle is more than enough to melt a piston if the thing is way too lean.  Jetting is also a bit more complex than you are suggesting.  Reading a spark plug is partly an art and is nowhere near as simple as most people think.

The OP needs to understand there are three overlapping circuits in a carburator.  The idle and off idle range is mainly controlled by the Pilot jet but of course the needle and the main jet are also allowing fuel into the airstream even when the throttle is completely closed.

The midrange is mostly controlled by the needle but of course the size of the main jet will make a difference.

The top end is mostly controlled by the main jet but the needle has an effect at anything less than WFO throttle.

OP, as someone noted previously, the oil content also affects the fuel content.  With respect to rich/lean we are talking about the air/fuel ratio, not the oil content.  As noted, increasing the oil content will reduce the fuel content which leans out the mixture.

The reason that a lean condition is bad is that the flame temperature increases, which can melt the aluminum piston.  Slightly rich condition leaves some fuel to act as a heat sink, reducing combustion temps.  Lean can also mean not enough oil is entering the engine to properly lubricate it, which can destroy the bottom end.  Depends on what is causing the lean condition.

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1 minute ago, CDNSXV said:

The motor must 100% be run under load.  Simply pegging the throttle with the bike in neutral won't tell you anything.  Three minutes of WFO throttle is more than enough to melt a piston if the thing is way too lean.  Jetting is also a bit more complex than you are suggesting.  Reading a spark plug is partly an art and is nowhere near as simple as most people think.

The OP needs to understand there are three overlapping circuits in a carburator.  The idle and off idle range is mainly controlled by the Pilot jet but of course the needle and the main jet are also allowing fuel into the airstream even when the throttle is completely closed.

The midrange is mostly controlled by the needle but of course the size of the main jet will make a difference.

The top end is mostly controlled by the main jet but the needle has an effect at anything less than WFO throttle.

OP, as someone noted previously, the oil content also affects the fuel content.  With respect to rich/lean we are talking about the air/fuel ratio, not the oil content.  As noted, increasing the oil content will reduce the fuel content which leans out the mixture.

The reason that a lean condition is bad is that the flame temperature increases, which can melt the aluminum piston.  Slightly rich condition leaves some fuel to act as a heat sink, reducing combustion temps.  Lean can also mean not enough oil is entering the engine to properly lubricate it, which can destroy the bottom end.  Depends on what is causing the lean condition.

I agree 100%, I just couldn't express it as well as you did.

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For oil ratio, anything in the 40:1 to 50:1 range will be fine.  Keep in mind that the higher number means less oil is added.

The suggestion to go back to stock jetting is a good one.  That is always the best place to start.

A 2-stroke running rich won't be all that obvious.  Typically the motor will be slightly down on power and produce black, oily spark plugs.

A 2-stroke running lean will likely feel like it is running super well and producing loads of power.  Lots of people will claim the bike was running awesome just before it ate its motor.

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If I forgot to mention that the plug chops, other than the one at idle, need to be taken under loaded conditions, I am sorry.

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Hey Guy's, so I've been doing some research and I've seen that the stock jetting is recommended for running at sea level, and I'm far from that by about 5,000 ft so should I still start off with stock jetting? 

Also the current jetting in my bike is ( 340 main) ( 45 pilot).

And the recommended stock jetting at sea level is (360 -370 main) and( 50- 45 pilot)

So I don't know what to do.   What are the effects off higher elevations lean rich???

I'm contemplating just running the current jetting from the people I bought the bike from because they obviously knew what they were doing and that bike has ran at this elevation its whole life. well actually there is about a 400ft elevation difference between were I live and where I bought the bike and if 400ft has a difference that would really piss me off.

What do you guys think?  And I was thinking about it and the few hours I got to put on the bike before I seized it, I recall it bogging pretty bad and it had a lot off black oil from the silencer and the plug was black and oily which would be signs of being rich right??

All this garbage makes me want to go with the girly 4 stroke power and avoid all of this. 

PLEASE don't take any offense from the above statement lol.

I actually think a four stroke would be cool to have for trail riding purposes.

Edited by Jack wagon

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Higher elevation equals less oxygen on each intake stroke which in turn equals the bike running richer.  That's why the main jet and pilot jet in your carb have been reduced in size.  The jet changes seem about right to me given you altitude.  Four strokes with carbs suffer from altitude changes just like a two stroke.  The new FI bikes may be able to compensate for the altitude changes some what.

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I'd run your current jetting. As you go up in altitude (actually, lower air pressure-Read about "Air Density", that is really what matters), you have less air, so the engine runs richer.

A 4S requires jetting for air density changes too.

 

You bike may of just been well past service limits when it failed last time.

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The float in the carb tries to maintain a "constant" level of fuel in the bowl so that the jets are sucking fuel and not air.  If the level is too low, the jets will start sucking air when the bike is going up or down hill and the engine will lean out and sputter.  If the level is too high raw fuel will leak out of the overflow tubes and possibly into the engine.

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