Type of riding kills plugs? - RM125

[Fultoncm]

I've got a 98 RM 125, new topend, reeds, exhaust, and carb that I think I jetted properly. I use Yamalube premix with 93 octane fuel. I've been buying the $10 NGK Iridium BR9EIX plugs instead of the $30 plug Suzuki recommends. I started doing a ton of riding in the woods and now this bike seems to foul plugs like crazy. I've gone through 3 in just 4, 2 hour rides. Luckily I carry a spare or I would have had a nice 7-8 mile hike with a 200 lb. motorcycle. up and down the Cascade mountains. It seems when I'm dogging around the bike will load up big time and I have to open up the throttle to clear it out. I'm thinking these plugs are fouling because I'm letting it load up too long before opening the throttle. Is this possible? Does riding around in the woods mostly on minimal throttle kill plugs? Should I get the $30 jobby?

Back to the jetting. Like I said, I think I've jetted it properly. When it's warmed up and I've opened the throttle a few times, the bike really runs great. But if I've been dickin' around in 1st gear not really getting on it, it does bog out a bit until I open it up a few times.

Any help would be appreciated. I've fixed so many problems on this bike and this is my last one! Then I move to Florida and start all over with my jetting problem :think:

 

[robwbright]

You should get the $30 plug because it has a reinforced tip - other plugs have a history of the tip breaking off in the RM125. Assuming you're in the right heat range with a similar plug, the $30 plug won't make any difference in jetting.

It sounds like your bike is not jetted right.

I ride in the woods 25-50% of the time - very tight single track. I have never fouled a plug since I got the bike in April 2005. Yes, mine will load up a bit, but never so much that it fouls.

What does the plug look like after a plug chop?

Spanky's jetting guide:

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. 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.
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.
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. The reason is simple. 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 rejet 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.

Warm the bike completely, and shut it off.

As already stated, start with the pilot circuit. Turn the airscrew 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 idleing. Turn the airscrew 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 airscrew for the best response.

Now is the time to determine if you have the correct pilot installed in your carb. The airscrew position determines this for you, making it very simple. If your airscrew 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.

Once you have determined (and installed it if it's necessary to change it) the correct pilot jet size, and tuned the airscrew for the fastest idle, it's time to tune the airscrew 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 airscrew 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 airscrew is not a set-it-and-leave-it adjustment. You have to constantly re-adjust the airscrew to compensate for changing outdoor temps and humidity. An airscrew 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.

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.

Once you have a little bit of experience with jetting changes, and you start to learn the difference in feel between "rich" and "lean", you'll begin to learn, just from the sound of the exhaust and the feel of the power, not only if the bike is running rich or lean, but even which one of the carb circuits is the culprit.

The slide is also a tuning variable for jetting, but slides are very expensive, and few bikes need different slides, so we won't go into that here.

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.

 

[robwbright]

BTW, I found the $30 plug for $23.

I bought one when I got the bike and used it all 2005.

I just bought another because it seemed like a good idea.

 

[Fultoncm]

Yeah, I just found the plug on rockymountainmc.com for $24. I just might get a few. Also found a couple on e bay.

The plug looks pretty good except the porcelain cone inside the plug is black. There's not much carbon on the spark arm. It's not wet from oil or fuel. It's really strange to me that only the procelain is black. When I run a test on these plugs they are sparking all over the place, not just on the arm. I'm going to have to print out these instructions and go through it tomorrow. I've got tons of jets for this thing.

Do you think changing the crankshaft seal will help? I've got one laying here. I have been getting a bit of smoke and spooge out of the exhaust.

 

[robwbright]

Do you think changing the crankshaft seal will help? I've got one laying here. I have been getting a bit of smoke and spooge out of the exhaust.

That's a possibility, but if I understand it, you'll usually see the oil level in the crankcase dropping if there's a problem with the crankcase seal.

If the porcelain is black, I'd guess that you're definitely too rich. That's would be the cause of the fouling.

Try looking here:

http://www.eric-gorr.com/techarticles/sparkplugs.html

http://www.ngksparkplugs.com/techinfo/spark_plugs/faq/faqread2.asp

http://www.off-road.com/dirtbike/tech/2002sparkplug/3.jpg

http://www.off-road.com/dirtbike/tech/2002sparkplug/4.jpg

"A lot of amateur tuners, some of whom are fairly successful, will look at some plug freshly removed from a two-stroke engine and offer advice based on the color of the oil deposited on the insulator nose. In fact, if the plug is hot enough there won't be any color, and if there is that still has nothing much to do with air/fuel mixture. If you think about it you'll realize that the only color you can get from an air/fuel mixture is the color of soot. When the mixture trapped in an engine's combustion chamber has more fuel than can be burned with the available air, then combustion will be incomplete and the excess fuel will remain as soot, which is not brown or tan or magenta or any color other than black. And if your engine's mixture is too rich, the sooty evidence will be present on the spark plug's insulator, in a very particular area.

You won't find any soot out near the insulator nose, on a plug that's running hot enough to keep itself from fouling, because temperatures there are too high to let soot collect. But the insulator is much cooler deep inside the plug body, and coolest where it contacts the metal shell, which is precisely where you "read" mixture strength. Look far inside a plug, where its insulator joins its shell, and what you'll see there if your engine's mixture is too rich is a ring of soot. If this ring continues outward along the insulator to a width of even a millimeter you can be sure the mixture is rich enough to be safe, and too rich for maximum output."

 

[darringer]

If your '98 is jetted the way my '99rm125 was jetted, it is ridiculously rich at the pilot jet. I believe it had a stock pilot of about 52 and I ended up at 42. After leaning out the pilot, I went to a 1/2 step leaner needle and adjusted that and the mixture screw according to temperature. I used the bike for everything from hillclimbs to very slow single track and never fouled a plug. I ran the expensive plug because I could run them until they were worn out ( about 6 months). I kept a cheaper plug as a backup, but never used it. After long low rpm runs, a couple of quick blips of the throttle were all that was needed to clear it out.

 

[Fultoncm]

Rob, thanks for that article. Now that I think about it, about the time the plugs are fouling I can smell fuel heavily in the air. I've looked at those photos of the plugs on the internet, but my plugs don't look much like any of them. I guess it looks like a cross between a good plug and a dry fouled plug. The only part that is black is the porcelain\ceramic electrode in the center. Which makes sense with the article you quoted.

Darringer, I've had a ton of problems with the carb on this bike. I ended up ditching the stock carb (Keihin PWM) and got one off a '97 (Keihin PWK). This made a HUGE difference for me. I jetted it according to the info on FMFs website since I have their exhaust. I'll definitely lower the pilot and see what happens.

Look like I'll have to take my tools, jets, and a few plugs with me out to the trail and spend some time working this out.

 

[2-Strokes 4-ever]

Our setup for our 98 RM125 in the woods.........summer: p-42, needle-1 slot leaner, m-168
winter: p-45, (needle stays same) m-170
Summer here means 70-95 degrees, and winter 45-65. (for colder riding we have played it safe and gone 1-step richer across the board.) Does not load-up with this tuning.

 

[Fultoncm]

Our setup for our 98 RM125 in the woods.........summer: p-42, needle-1 slot leaner, m-168
winter: p-45, (needle stays same) m-170
Summer here means 70-95 degrees, and winter 45-65. (for colder riding we have played it safe and gone 1-step richer across the board.) Does not load-up with this tuning.

Awesome! I do have a few questions though. What exhaust are you running on it? What reeds? Where is your needle clip? Does you carb look like this: http://www.keihin-us.com/pwk.htm
or like this: http://www.swedetechracingengines.com/parts_accessories/pictures/cr125-carb_548x480-099c.jpg

Shyte, I just looked and I am running a 50 pilot, 4th position on the needle clip, and a 168 main. I am really beginning to think my pilot is way to rich.

 

[nikki]

This might sound simple, but maybe try a BR8ES. It's like a $3 plug available at most auto parts stores. I ran a BR8ES in my '98 RM 125 (I raced MX two seasons with that bike, maybe 60 MX races and a bunch of play hours). I also ran a BR8ES in my YZ 125. It's a hotter plug, should help fouling at lower RPM rides. If you're worried it's too hot of a plug, then put in one, go for a short wide open ride, and check that the plug is tan, not whiteish, just to be sure.

 

[quik720]

Ive had nothing but bad luck with NGK's on my RM. BEST plug I have ever used, and still currently use are (Champion Powersport) '8902'....

 

[Fultoncm]

Quik, where are you getting those?

Nikki, I'll pick up a few of those and give them a try.

Thanks all!

 

[2-Strokes 4-ever]

Awesome! I do have a few questions though. What exhaust are you running on it? What reeds? Where is your needle clip? Does you carb look like this: http://www.keihin-us.com/pwk.htm
or like this: http://www.swedetechracingengines.com/parts_accessories/pictures/cr125-carb_548x480-099c.jpg

Shyte, I just looked and I am running a 50 pilot, 4th position on the needle clip, and a 168 main. I am really beginning to think my pilot is way to rich.

It's the second carb pictured (sweden site). Needle is stock, but in third slot (from top). FMF Fatty, FMF turbine core SA silencer, CarbonTech "low-end" reeds. Always ran a NGK B8ES. Also, adding about 3-4 exhaust manifold washers and siliconing pipe real well will help get you some low-end snap.......at a slight cost of top-end.

 

[quik720]

Quik, where are you getting those?

Wal Mart of all places!!! $1.58 each

 

[sunnyboy]

OK--this is the deal--your running rich in the middle the mixture off idle to just before wide open. this mostly contolled by your needle,dropping the clip on the top of the needle will lower the needle causing it to lean out in the middleand will solve your problem.only move it one notch.

 

[Fultoncm]

Thanks Sunnyboy. I'll give that one a shot once I get this bike back on the trail. I was hoping to get it out this weekend but I discovered the suspension linkage is trashed...waiting for parts.