How to clean fouled plugs...or not foul them :)

[Joshua250]

Hi all,

I bought this bike (05 CR125) second hand about 1 month ago, the bike has been raced with the previous owner but I will be mainly trail riding. On my first ride day (2 hours trail riding) I fouled 4 plugs (2 x BR9ES, 2 x B8ES), I was using 30:1 mixture then but after that I started using 40:1. The second time I went trail riding with the bike I had a BR8ES in the bike which lasted about 3 hours until it fouled (came out very black and slightly oily). After this the next plug fouled in 10 minutes, then another in 10 minutes, then another straight away as I started the bike up. (Not sure how long since last top end)

What could this be, clogged carby jets? needs top end? I really don't know. Even though I am trail riding I am riding it in power band regularly.

Thanks,

Josh

P.S How do i clean fouled plugs and will the work like new?

[Mike38]

How to not foul a spark plug, lesson #1.

Sell the two stroke and buy a four stroke.

End of lesson.

Any questions?

[Soul Man]

Fouling plugs would mean you are too rich. Also, some 2 strokes will foul if you idle or opertate at low throttle settings for extended periods. If you are doing slow technical trails it may foul more easily (although you say you are riding it in the powerband). make sure you shut it down when you stop to rest, even for just a minute, that may make a difference. I'd lean the carb.

[SXF811]

It's a rule two strokes need to be revved to keep the plug clean and from fouling, the mixture seems right at 40:1. Your not like over oiling your airfilters or something? I admit buying the four stroke would solve the problem ha ha, but if you like the two stroke then stay with it.

[needsprayer]

If they are new and fouled I clean them with my homemade spark plug cleaning setup. They run like new.

https://www.thumpertalk.com/forum/showthread.php?t=497914&highlight=cleaning

[MXOldtimer]

I have in the past but, I'm not a fan of reusing oil fouled plugs.

You need to learn how to "JET" your bike properly. Search on line or better find someone in your area that has knowledge about jetting and have them help explain and teach you.

I ride a smoker and have used 2 plug in the last year. I changed the last one just prior to a very long ride just to be on the safe side.

Learn to jet and you'll have no problem.

.

[808hondacrguy]

Rejet yur bike and roost with no worries.If the jetting is stock,then it is WAY too rich,especially for slow trail riding. Raise youre clip on yur needle and drop the pilot one to start. ? for 2 strokes!?

[Rip Wheeler]

Hi all,

I bought this bike (05 CR125) second hand about 1 month ago, the bike has been raced with the previous owner but I will be mainly trail riding. On my first ride day (2 hours trail riding) I fouled 4 plugs (2 x BR9ES, 2 x B8ES), I was using 30:1 mixture then but after that I started using 40:1. The second time I went trail riding with the bike I had a BR8ES in the bike which lasted about 3 hours until it fouled (came out very black and slightly oily). After this the next plug fouled in 10 minutes, then another in 10 minutes, then another straight away as I started the bike up. (Not sure how long since last top end)

What could this be, clogged carby jets? needs top end? I really don't know. Even though I am trail riding I am riding it in power band regularly.

Thanks,

Josh

P.S How do i clean fouled plugs and will the work like new?

Well, several ways to get a fould plug working again. A propane torch, get the porcelain glowing and let it cool. Also, a spark plug sandblaster works great. But I'd find out why its fouling. Its over rich. Air filter spotless? Someone mess with jetting? Going 40:1 was a good idea. Move the jet needle down a click (circlip up a groove) and make sure the air screw isnt too far closed.

[Soul Man]

Also remember that changing your oil ratio changes your jetting. By decreasing the oil (from 30:1 to 40:1) you increased the amount of gas in each x volume that your motor sees and made it richer. If you were rich to start with that may have made it worse. Remeber, the oil doesn't enter into the equation for rich/lean, just the amount of fuel and air. You could seize a motor by adding more oil since it will lean out and detonate, whereas you think you are protecting the motor with more oil.

If you get your jetting spot on, and then ever change your oil ratio, you will likely have to rejet.

[520ditchwitch]

Joshua, start with getting the correct adjustment on your idle air screw. If you need directions on how to do this, let us know. On the many 2 strokes I've owned, most plug fouling issues, when I had them, were cured by that adjustment.

[howell]

adjust the air, fuel, idel. since the guy raced the bike before you these are probely all changed up from stock.

[kx_rider53]

1) Dont switch the oil:gas ratio to fix plug fouling.

2) Set your float

3) Make sure the bike is in sound mechanically coniditon (clean air filter, fresh top end, etc).

4) Jet leaner

The rich jetting does not allow piston crown temps to get to the right temperature thus not burning all of the oil, causign a foul.

Keep the 30 or 32:1 ratio with a good premix and good gas. You can use a 9 or 8 heat range plug, just keep it consistant.

Here is a good article on jetting,

Spanky's jetting guide

Throttle Ranges:

Pilot Jet/air screw:0-1/4.

Needle Jet:1/4-3/4

Main Jet: 3/4-Full open

I got alot of this from spanks of dirtbike.com so dont give me the credit!

Jetting 101:

A correctly jetted carb makes a tremendous difference in the torque, midrange pull, top-end pull, and over-rev of your engine. If you have never jetted your bike correctly, you will almost certainly gain some performance at some point in the bike's powerband.

A cleanly jetted pilot circuit can be the difference between having to clutch the bike out of a turn or not. Hard starting when hot or cold, poor response when opening the throttle, reluctance to idle, all of these are symptoms of an improperly sized pilot jet or incorrectly adjusted air screw.

The needle can make all the difference in the world for the power of the machine in most situations, as it controls the throttle range that most riders spend most of their time using.

A correctly sized main jet could mean the difference between being able to rev out high enough to not have to shift one more time at the end of the straight, or the power falling flat on top and requiring you to make that extra shift.

Are you fouling plugs? Many people will tell you all sorts of band-aid fixes, from running less oil, to running a hotter plug. Both are incorrect fixes for plug fouling. It's all in the jetting. An engine that is jetted too rich will have combustion temperatures that are too low to burn the fuel and oil effectively, leading to deposits and wet fouling of the plugs.

Do you have spooge? There are the rare instances where a mechanical issue, such as a leaking wet-side crank seal, can cause spooge. But, by and large, this isn’t the case. In most instances, spooge is caused by rich jetting. It has nothing to do with how much oil you mix in the gas, or how hard you ride. An engine that is jetted too rich will have combustion temperatures that are too low to burn the fuel and oil effectively, resulting in deposits, plug fouling, and spooge. Spooge is nothing more than unburned fuel and oil entering the exhaust.

The only way to know what jetting changes you will need is by trial-and-error. No one can give you jetting specs, because every bike is different, every rider has a different style, and jetting is totally weather dependent. Unless the person telling you what jets to use is riding an identical bike, on the exact same track, at the same time, his recommendations are meaningless. Someone with a good understanding of jetting can get you in the ball park, but you need to do the testing to determine the correct jetting yourself if you want it right.

Jetting is fairly simple, and is a useful skill to learn if you ride a two-stroke and want it to perform at it's best.

It's very important that you start with the pilot circuit, because the pilot circuit affects the entire throttle range. When you are at full throttle, the main jet is the primary fuel metering device, but the pilot is still delivering fuel as well, adding to the total amount of fuel that your engine is receiving.

Before you start to re-jet your bike, you need a clean air filter, a fresh plug (actually you need several plugs to do plug-chop tests for the main jet), and fresh fuel.

One important detail: Make sure the engine is in good mechanical condition. If your engine has a worn top-end, fix it first. Trying to jet a worn out engine is a waste of time. The same goes for reeds that don't seal properly, and a silencer that needs re-packing. Worn reeds will mimic rich jetting, and worn rings will mimic lean jetting.

Before you start the jet testing, Install a fresh plug. Set the float level to the proper specs, an incorrect float height will affect your jetting all across the throttle range.

All jet testing must be done with the engine at full operating temperature.

As already stated, start with the pilot circuit. Turn the air screw all the way in, then turn it out 1.5 turns to start. Start the engine, and turn the idle screw in until you get a slightly fast idle, or hold the throttle just barely cracked, to keep the engine idling. Turn the air screw slowly in, and then out, until you find the point where the idle is fastest. Stop there. Do not open the screw any farther, or your throttle response will be flat and mushy, and the bike may even bog. This is only the starting point, we will still have to tune the air screw for the best response.

Now is the time to determine if you have the correct pilot installed in your carb. The air screw position determines this for you, making it very simple. If your air screw is less than 1 turn from closed, you need a larger pilot jet. If it is more than 2.5 turns from closed, you need a smaller pilot jet. If your engine doesn’t respond to air screw changes, then you either have a dirty carb, or the pilot jet is way too rich. When the pilot jet is way too rich, you are forced to use the idle screw to open the slide so far in order to keep the engine running that the pilot circuit is partially bypassed, and the engine is actually starting to draw fuel through the needle jet.

Once you have determined (and installed it if it's necessary to change it) the correct pilot jet size, and tuned the air screw for the fastest idle, it's time to tune the air screw for the best throttle response. Again, make sure the bike is at full operating temperature. Set the idle back down (the bike should still idle, despite what you read in the Moto Tabloids), and ride the bike, using closed-to-1/4 throttle transitions. Turn the air screw slightly in either direction until you find the point that gives you the best response when cracking the throttle open. Most bikes are sensitive to changes as small as 1/8 of a turn.

The air screw is not a set-it-and-leave-it adjustment. You have to constantly re-adjust the air screw to compensate for changing outdoor temps and humidity. An air screw setting that is perfect in the cool morning air will likely be too rich in the heat of the mid-day.

Now, it's time to work on the needle. Mark the throttle grip at 1/4 and 3/4 openings. Ride the bike between these two marks. If the bike bogs for a second before responding to throttle, lower the clip (raising the needle) a notch at a time until the engine picks up smoothly. If the bike sputters or sounds rough when giving it throttle, raise the clip (lowering the needle) until it runs cleanly. There isn't really any way to test the needle other than by feel, but it's usually quite obvious when it's right or wrong. A too-rich needle can often be felt simply when revving the bike on the stand. The bike will sound rough and raspy when blipping the throttle on the stand. A correctly jetted bike should rev cleanly and crisply.

Last is the main jet. The main jet affects from 1/2 to full throttle. The easiest way to test it is to do a throttle-chop test. With the bike fully warmed up, find a long straight, and install a fresh plug. Start the engine, and do a full-throttle run down the straight, through all gears. As soon as the bike tops out, pull the clutch in, and kill the engine, coasting to a stop. Remove the plug, and look deep down inside the threads, at the base of the insulator. If it is white or gray, the main is too lean. If it is dark brown or black, the main is too rich. The correct color is a medium-dark mocha brown or tan.

Please note that, when reading plugs, the tip of the insulator, threads, etc. are meaningless for jetting purposes. They can tell you a lot of things, but jetting isn’t one of them. Only the mixture ring at the very base of the insulator, inside the threads, can tell you anything about the jetting.

These links should help you to understand reading plugs:

http://www.tsrsoftware.com/images/sparkplug.gif

http://www.tsrsoftware.com/read-plugs_files/sparkplug b-w .gif

The slide is also a tuning variable for jetting, affecting the throttle range from 1/8 throttle to approximately 1/3 throttle. If you can’t clean up the small-throttle jetting on your bike no matter how lean you go with the pilot or the needle, the slide is the next step. But few bikes need leaner slides.

Keep in mind, even though this article is intended primarily for two-strokes, four-strokes also need proper jetting to perform right, although they are not quite as fussy as their oil-burning cousins. The only real difference in the two is with the pilot circuit.

Two-strokes have an air screw that you screw in to make the jetting richer, and screw out to make the jetting leaner. Four-strokes, on the other hand, have a fuel adjustment screw that you screw in to make the jetting leaner, and out to make it richer. Their purpose is the same, they just do it in different ways.

Four-stroke carbs also use an accelerator pump. By nature, four-stroke engines have a much weaker vacuum signal to the carb at small throttle openings, so they tend to hesitate when whacking the throttle open, because it takes a small amount of time for the weaker vacuum signal to begin drawing fuel up through the jets. To compensate for this, the accelerator pump squirts a small stream of fuel into the carb throat. The accelerator pump must be correctly adjusted for flow volume and timed for flow duration. Too much fuel squirt, and the bike can flood, especially on a tight track where frequent off-on throttle transitions are necessary. Too little, and the bike bogs coming out of turns and when landing from jumps. Every four-stroke model is different, so refer to your manual for correct adjustment of the accelerator pump.

[TeamTurtle]

Here's another (short) article on jetting. Well worth the read.

http://www.transworldmotocross.com/mx/how_to/article/0,13190,1018579,00.html

Once you get it properly jetted for the type riding you'll be doing, you'll love your bike.

(And ignore those evil 4-strokers - they have a lot more to worry about than just fouled plugs.)

[ImprtTunr]

Not sure its going to make a huge difference but you are using the wrong plug for the bike (per the mfgs requirement anyway). The proper plug is a BR9EG. I used to own a 2002 CR125 and had some of the same issues. If it were my bike I would go one heat range hotter on the plug (which is what I did on my own bike). I would start running a BR8EG. That alone helped me considerably. Then I would work on getting the jetting closer.

[velosapiens]

How to not foul a spark plug, lesson #1.

Sell the two stroke and buy a four stroke.

End of lesson.

Any questions?

i have a question. how come i have only ever fouled 1 plug in 20,000 hard offroad miles on 2 strokes (when i squished the pipe almost flat), and my buddy with a yz426 fouls 1 every week or two?

to the OP, most of the time, plug fouling is a jetting issue. if your bikes too rich ( jetted for winter but now it's summer, airfilter dirty or clogged, etc...) you might foul a plug. modern 2-strokes only foul plugs when something is pretty seriously wrong. i've seen plenty of bikes jetted so rich they would hardly run, but still no fouling. go figger. not sure what kinda powervalve actuation them hondas have, but that could possibly be an issue too, as could really worn rings. first things first tho, make sure the jetting is in the ballpark.

[comeau242]

How to not foul a spark plug, lesson #1.

Sell the two stroke and buy a four stroke.

End of lesson.

Any questions?

I had no problems what so ever, no hesitation or much oil or carbon on plugs, although my bike is set perfect for what im runing it at. i run Full-synth 50:1 mix. high quality, i also ride alot trails and low-mid rpm's i have only fouled once by accident, my dad mixed it instead of me and put too much oil.

[Keyes]

How to not foul a spark plug, lesson #1.

Sell the two stroke and buy a four stroke.

End of lesson.

Any questions?

Fouling plugs vs. Floating valves?

I'll take a fouled plug...

[hondacrf250rmx]

How to not foul a spark plug, lesson #1.

Sell the two stroke and buy a four stroke.

End of lesson.

Any questions?

haha great idea!

[One2nine]

It's a rule two strokes need to be revved to keep the plug clean and from fouling, the mixture seems right at 40:1. Your not like over oiling your airfilters or something? I admit buying the four stroke would solve the problem ha ha, but if you like the two stroke then stay with it.

I don't know what rule book your read...

A perfectly jetted (or close to) 2 strokes will almost never fould a spark plug. I've fouled more plugs in my yzf screwing with jetting than I have in any 2 stroke I've ever owned. Pick a ratio, pick a fuel, and jet for the conditions. Simple as that. It's not rocket science.

And if anyone even tries to tell you to mix and match your oil ratio, back hand them.

Edit: holy hell this is old!!!!