Hi,
I am rejetting my YZ125 which is running rich with a #30 pilot and #430 main. I have gone to the TT store and ordered the next three sizes down in both pilot and main jets, as well as the next size up for both jets to cover all bases. I was under the impression needle sizes were a choice between stock (which I was going to stick with) or custom ones for the hardcore riders, but I saw about 10 different sizes, and not a single one seemed to be stock.
My question is, is there a one size fits all needle that I can get for those jets, or do I need to pick a few? Does each one fit a specific range of main jets? Also which needle(s) will I need?
Thanks

Also should add, most of my riding is done between sea level and 1000' with the occasional trip up to a place that is 3000'.
Temp between 10degrees celcius and 25degrees. At the high altitude it can go as low as 0, any colder and chances are I won't bother riding! Bike is stock as far as the motor goes.

Hello,

Depending on what you are trying to accomplish relays directly to what needs to be done. If we have a bike that is running rich we dont generally have to tune the carb to fix this concern. What are we mixing the oil/gas, what has been done to the bike, what plugs are installed? This type of information will help tune it in the best. Generally when we do any mods to the carbs it would be for serious racers or performance modifications. Let me know what ya got!

Ktmhiflyer, on 30 May 2012 - 11:06 AM, said:

I am mixing yamalube at 50:1, a low ratio I know, but I don't race, and the engine doesn't get thrashed as hard as most 125's.
No mods to bike at all....but it is due for a top end, which has led me to the decision to just give the carb a clean out, replace the top-end and see what it's like from there before I go through with new jets.
Bike has always run rich IMO as it bogs quite easily, and seems to top out too early, and plug is coming out black and slightly tarry, however it doesn't foul to the stage where it stops running. I will get back to you on what plug it has got.
My main question is, what dictates which needle type get? will certain needles only suit specific main jets? Is there a relatively generic one I can get that will function exceptably for most jetting set ups?
Thanks for the reply.

50:1 is a good mix it keeps the bike running fairly well. Generally with this mix I would prefer running a NGK BR8ES spark plug, generally the next step up in heat range elminating the bog and fouled spark plugs. As for the needle to be honest most bikes that I rejet keep the factory needle I will either adjust the clip up or down a few notches depending on what I am trying to do. Most cases when a needle is changed is when a carb has had the main jet increased 5-10 sizes and the needle is super sloppy inside of it. At this point for you I would recommend a BR8ES plug, this will more than likely take care of all of you problems. Another thing to keep in mind is a two stroke is not designed to idle if it idles it will carbon up easily all of my bikes have the idle adjustment screw turned down so they will stall if you are not feathering the throttle. I do alot of racing so this is one reason I like to keep me bikes cleaned out. For a occasional rider as yourself a idle will not hurt the motor we just need to remember that the bike will need to be cleaned out after a long idle or it will feel boggy. The topping out of the bike again is not a carb issue it would be a gearing issue and this can be changed by swapping sprockets in the front or rear of the bike. The smaller the rear or front gear the faster the bike will go top end. This will also load the motor down and cause the topping out to seem faded. Try the plug and let me know what you think!

Will do and I will let you know how it goes, we are just coming into winter over here so I may not get to try it out properly for a while though. Thanks for your help.

Winter already? Wow climate shock, we are just entering summer here! Barely out of spring!

I'm not sure what stock jetting specs are for your bike, but with a quick search or a peak in the owner's manual, you will know.  (it's a good starting point for the fresh stock engine)  If it's low on compression it will run rich.

From what I can tell the type of riding you do you won't need to fuss over the jets.  I think you will want to just get it to run clean and forget about it.

With that said run-ability and air fuel ratio can be a very involved subject but from what you describe I will give you a few quick pointers.
Run the stock spark plug.  The plug has no effect on determining rich or lean.  Most two stroke dirt bikes come from the factory slightly rich, in general moving one clip leaner on the needle will solve most issues for the non-picky racer.  If you search the phrase "plug chop test" on the net you will find detailed methods of checking and setting the jetting.

In your case I think if you set the air screw on the lean side of the adjustment range go the smallest step leaner on the pilot (slow jet) and one clip leaner on the needle and possible one step richer on the main you will be good.  It will idle, rum smooth and clean all the way to the top and have enough fuel at the top for good power.  That will most likely get rid of the spooge on the pipe.

I didn't really want to get into this part, but I can't help but state my opinion.  The oil that you mix with the fuel is what lubricates the crank bearings, connecting rod bearing, and the rest of the top end.  The oil uses the fuel as a transport into the cylinder.  Many people think that if there is excess oil coming out of the pipe that must mean there is too much oil in the fuel, Not True!  It means during the combustion process all of the fuel and oil is not vaporized.  Most likely it is too rich!  By you running less oil in the fuel you are giving the bearings less lubrication just as if the engine was too lean in air fuel ratio.  There is a fine line as to how much oil to fuel ratio in regards to proper lubrication and horsepower numbers but for the average pilot, wouldn't you want to give your engine as much lubrication as you can?  To put it in perspective, you are running 2.5 ounces of oil per one gallon on fuel. (1:50)  I run 5 ounces of oil to one gallon of fuel in my son's two strokes.  (1:25)  (most people state this 50:1 or 25:1)  The intelligent argument states that I sacrifice a slight amount of HP because of all the oil in the fuel.  (basically I am replacing some of the fuel with oil so there is not as much fuel to burn and make HP)  and that is accurate, but doing it my way I don't need to put crank and connecting rod bearings in it every other top end.  You can do it any way you like, that's been proven, but I recommend more oil in the fuel.

As far a the needle goes, they make so many different ones because the needle covers such a large throttle opening.  (1/4 to 3/4)  The numbers and letters on the needle are code for clip height, diameter, length, and taper.  One can make very fine adjustments to a specific part of that 1/4 to 3/4 by changing a specific part of the needle, but the average rider will never notice it.  I recommend you find the stock needle and then you can just try different clip heights so you can feel the difference.

I agree with what is said, as for the 25:1 vs 50:1 if we run the same mixture on the same bike with the same carb settings the bike running 25:1 will foul plugs and runner a more dark/ black spark plug then a bike with 50:1. I am not trying to argue the point I am just advising from 6+ years at the shop. The fact that is is designed to lubricate is 100% correct but if we take a sample of fuel at 25:1 mixture and then sample of 50:1 mix and burn them at the same time. The 25:1 ratio will burn slower then the 50:1 ratio due to the fact there are twice as many oil particles in the fuel restricting the burning process. This has been shown to carbon a bike and I truthfully see this on a weekly basis. All in all everything that was stated is correct and it is a different take on each subject. I can tell you from experience and 100's of bikes that what I state is safe and truthful

Ktmhiflyer, on 01 June 2012 - 09:52 AM, said:

So at this point If I understand you correctly you want to treat this guy from New Zealand like a customer and advise him to run less oil in his fuel so he doesn't need to jet properly (which is his original intent) and so he doesn't carbon his bike.  (did I say that correct?)

I guess I am just curious, is your argument for more oil in the fuel or less?  If the carb. is jetted properly do you think the byproducts that build up would be more, or less, or about the same comparing the two ends of the spectrum on accepted oil to fuel ratios?

Why would the average rider not want to use as much lubrication as possible in the engine?

Edited by kx450f63, 01 June 2012 - 12:14 PM.

kx450f63, on 01 June 2012 - 12:07 PM, said:

You are taking this the wrong way, everything I have said is friendly advice that will generally key in on a certain problem. I stated that from previous experience I have seen where mixing the fuel/oil ratio to rich can cause excessive carbon. If you have a motor that is operated at 25:1 and 50:1 and take them both apart the 50:1 motor will be a much cleaner motor with alot less carbon. Oil leaves carbon traces no matter how you want to look at it. Not all the oil in the fuel is going to stick to the crank, bearings, walls, ETC some will make it back to the combustion chamber and burn. When we do this we need to understand that the more oil in the fuel the more oil that will be burned.

Now taking what you stated earlie as more air less fuel theory which is how a carb works, now if we add more air and less fuel in turn we are adding less fuel and oil, but this does not seperate the fact that the oil concentration is still the same if we change jets or not. If we move the oil mixture up and a common rider preference that 90% of racers are using and the bike operates properly or atleast better, wouldnt we say that would be a some good advice. I am not telling him to run straight gas and  hurt the motor it is strictly ADVICE and a good thing to try.

I love all aspects of motocross and anything that has to do with them. When I supply advice to someone it is not something I am pulling out of a hat, it is something that has been done and has helped. Now on the other hand if the bike is way out tune or adjustment which I am assuming this one is not seems he is looking for top end and needle recommendations you are right this would not be the way to go about it. But we are not in that situation and sometimes it is better to lead someone in a general direction rather then have them swap all kinds of parts that they may or may not know what they are changing. Not every one knows what the pilot controls, main jet and so forth. So in no way at all was I being contrascending I was offering friendly advice I would offer someone at the track or on a trail somewhere. I hope I have not offended you in any way just here to share the previous experience I have had and found to be helpful.

Thanks both for your replies. As for the oil ratio, given it's causing quite considerable deposits on my spark plug and splooge on the chamber, I think the quantity of oil getting to the engine is sufficient, after a rebuild and a clean up of the carb I may check it out again and consider changing the ratio. For now I'm confident it's getting more than enough.

By the way, stock jetting for the YZ 125 is 410 main and a 40 pilot. my air screw is 2 turns out.

kx450f63, on 01 June 2012 - 09:01 AM, said:

I just reread this part, interesting. After I do the top end I might consider making some changes to the ratio, but only a little, opinion on what ratio to mix too seems devided even among the experts, but it is something I will consider.

Interesting no one has mentioned doing a plug chop to see where the bike is running rich. You'll need a few new plugs to do it but I think it's the best way for a home mechanic to see where changes are needed.
I agree that if the bike is basically stock there's no reason to change out jets/needles. Could be just a half turn of the mixture screw or  lowering the needle a notch or two.
Motorcycle companies always send the bikes out with rich settings so the user doesn't melt the piston while it's under warranty but it's not that far off where it's supposed to be.
The point about idling is a good one as well. Two strokes hate it.

Found this old thread http://www.thumperta..._1#entry8941195

So this is what I need to do?

Indorider, on 02 June 2012 - 06:16 PM, said:

Take a look at post #8 in the third paragraph.

My two strokes don't have any problem idling,  it's all in the jetting.

kx450f63, on 04 June 2012 - 04:23 AM, said:

Damn! Missed that. My two strokes don't have a prob idling either but I wouldn't want them to sit idling for more than a couple of minutes without some "clean out" revs during that time.
I do run them just a tad rich (dark chocolate brown plug) because they are both difficult to get parts for. It's the price I pay for liking rare two stroke street bikes.

Indorider, on 04 June 2012 - 02:32 PM, said:

I don't see anything wrong with that thought process.

My son rides at a fairly high level for his age (10) and spends much less time on the slow and needle jet than on the main.  In my experience I can keep the slow and needle fairly lean and keep the main as fat as the engine will tolerate.  It will idle all day like this with no issues.  It will roll up to 3/4 throttle very clean and quick.  When he's on the main jet it barks well, which is the majority of the time.  I keep the main as fat as possible because that's when he needs it the most.  The engine is under the most load, most rpm, and most heat, therefore needs the most lube then.  In our case he is not cruising much on the needle (usually just blows rite through it on the way to the main)  so that circuit can be on the lean side to help keep things clean.

In the case of a woods bike, trail rider, or street bike I would keep the pilot lean, and try to get the needle as close to perfect as possible and the main just slightly rich due to the fact that these riders will likely be cruising on the needle the majority of the time.

Thumbs up on the two stroke street bikes.

kx450f63, on 05 June 2012 - 04:31 AM, said:

Great logic on all points...