Misfiring at low revs

[sh123469]

I have noticed recently that when I turn a corner nice and slow, sometimes my bike misses on one cylinder a little before I speed back up. This is the only time it misses.

I checked my plugs tonight thinking it might be one of them. Both were gapped at .020 so I re-gapped at .025. Bike sounds a little better and seems like it might pull just a little harder. But, the low speed miss is still there.

While I was looking around, I noticed that the PO had butted up the connections from the air box but didn't reconnect them. After spending all the time trying to get them on, I know why. That air box is some kind of torture device. I just hope I remember the combination to get it back on next time.

Now, the miss, I'm thinking it must be carb related since the plugs made no difference. I have noticed that sometimes with no load like going slightly downhill and the engine is just turning freely, neither pulling or dragging, I hear one cylinder sputtering. I have been figuring this was carb related.

What do you all think about this problem?

A little info. 2005 Ninja 250, no mods, bone stock except the PO removed the baffles from the very back end of the mufflers, 14,400 miles on it. Just put gas in it 5 days ago and down to about half a tank now. Always run reserve a couple minutes after filling up, so it shouldn't be a water problem. Nothing but gas came from the bowls when I drained them to see if there was water.

[Ghostt]

Did you disassemble, cleaned the spark plug caps? Renew the ignition wire ends?

[sh123469]

I did not. Are they known to be a problem on this bike?

The caps fit nice and tight. The wires look good, no scrapes or anything and fit nice and tight at both ends. I'll pull the tank and take a look at the caps and renew the wire ends today just to make sure.

[Ghostt]

Make sure you disassemble the caps, and clean them, and yes the caps get cruddy.

Here my write-up,

Short explanation: The inside of the hard plastic caps accumulate crud the can short out the spark. This can cause rough running or failure to start. Every time you do any work on the bike: remove them disassemble and clean them and renew the wires or at least the connections.

The long Explanation, Warning engineering information can cause Drowsiness.
The ancient cylinder design of the engine dictates that the spark emanate form the center of the combustion chamber. In order to get it there, the plugs had to be located down deep in a well between the cams. This well is a perfect place for dirt and moisture to accumulate. Then because there is no cooling water at this point the metal around the plug runs very hot. Surround this with the large amount of cool metal and you have a recipe for condensation. Now K did drill a drain hole between the fins to help (a little) but it often gets plugged up.

The moisture boils off the base of the plug and the vapor condenses on the cool plastic cap and the plug insulator. This moisture forms a easier path for the electrons to ground than jumping the gap at the plug to make a spark. Misfire.
This issue is right up there with Pilot jets as a cause of trouble.

Here's some pictures that might be helpful. I took these when I replaced the wires themselves, as it was a good time for a write-up, and the wires were OEM from 1998.

Wires are just 7mm copper core, with clear silicone jacket

[xXecuterXx2]

@Ghostt, i swear you live on these forums don't you? Lol, love that dedication.

[Ghostt]

@xXecuterXx2 just doing my part, and I love being able to help, and having the time to do it.

I remember back in the day learning things was different before the internet, it's an awesome tool for learning, and helping out.

Sharing my knowledge and experience with anyone willing to read it, and hopefully saving them time and money, and most importantly downtime.

[sh123469]

So, I didn't have a chance today to check it out. I'll try to get to it tomorrow between driving the wife to work and going to the big meet in Chesnee. If not, I will try to get it sunday.

You mean you can actually still buy spark plug wire with actual wire in it? So, how come we have a resistor plug cap and a resistor plug. Why are we trying to reduce the voltage to the spark plug? I always thought the idea was to get the voltage and current to the electrode. Resistors do just the opposite. I realize that resistors do help cut ignition noise in the radio but how many of our bikes have radios on them?

Thanks for the pics. That sure gives a good idea of what to do and look for when I do it.

[xXecuterXx2]

Originally Posted by Ghostt

@xXecuterXx2 just doing my part, and I love being able to help, and having the time to do it.

I remember back in the day learning things was different before the internet, it's an awesome tool for learning, and helping out.

Sharing my knowledge and experience with anyone willing to read it, and hopefully saving them time and money, and most importantly downtime.

Ey man, you've definitely done so, speaking from personal experience here

[Ghostt]

Okay here's the answers you seek,

It’s quite normal for Non-Quantum Physics’ to think of sparks as a thing that happens instantly like, Wham Bam Thank You Mam.* Not so.

A spark, as in a spark plug in an engine, has a* pre- period (think foreplay), a strong build up (intercourse), a climax (well yeah), and even an after glow.

OK, enough sexual innuendoes.

When your engine’s timing system sends the message to the Ignition system that, "It would be nice if you fired a plug about now", a lot happens in sequential order.* For this description, we’ll start after the coil is saturated and has received the signal to fire a plug.

Electrons of energy start to flow down the plug wire, happily on their way until they reach the break in the wire (the plug gap).* They then stop and mill around like wildebeest waiting to cross a river.* More and more electrons pile up behind the ones at the edge and build up in the plug wire and the center conductor in the plug.* As this pressure builds, an intense electric field is created in the gap to the ground element.* When the ignition system has fed enough electrons down the wire, the ones piled up at the gap are milling around faster and faster and the crowd gets thicker and thicker.* As the intense field created just starts knocking electrons off the edge, the gap then becomes Ionized.* The Ions in the gap provide a set of stepping stones. The electrons then begin to flow across the gap.* This flow becomes a rush and the space is so crowded that there is a lot of friction created by the mass of electrons tying to go somewhere.* The heat created by the friction is what we call “Spark”.

That’s the simple explanation.* Now about* Spark Plugs.

Electrons in the center conductor of the plug are bound there by an electrical force call “work function”. This* can be overpowered by sufficient energy.* The binding force is lessened the hotter the metal is. This is the biggest reason the center wire of a plug is insulated from the body, more so than for electrical insulation. The hotter the wire is, the better the spark action. Now you can quickly exceed the melting point of common metals, so exotics are chosen for this part, again not for their electrical conductive properties but for their heat resistance. These metals, like Platinum, are expensive.* You would think that the reason the electrodes are tiny in the pricey plugs is because of the cost of the metal.* Nope wrong again.

The ease in which the electrons are knocked off the electrode is improved by the sharpness of the edges.* As each electrons leave the electrode to journey across the gap, it takes a bit of the electrode with it (like packing a sandwich for a trip).* As the edges of the electrode become rounded, the force necessary to cause a spark to jump the gap is greatly increased.* Couple this activity with the heat thing, and you have the reason for the exotic metal.* The hotter the electrode is made to run, the less likely it is to foul.* So when you look at your plugs, don’t worry too much about the color, but look very hard at the sharpness of the edges of the center electrode.* When you can see a rounded shape, discard that plug.

Right here is a good place to bring up heat range marking of plugs.* Contrary to popular notion that the spark strength is what’s indicated, it’s really the temperature that the electrode runs at.* This can be judged by examining a plug’s insulator.* The deeper the groove is around the center wire that the insulator surrounds, and the longer the path is for the heat traveling to the body of the plug has, the hotter the electrode runs.* Conversely, if you examine a cold plug designed for racing, the insulator is nearly flush with the tip of the electrode.

The tiny size of the electrode is also not to conserve expensive metal, but to reduce the size of the electrode to provide a small an “Edge” for the electrons to pile up against.* This is the primary reason the plug resists thermal breakdown longer.* This, and unleaded gas, is why you have plugs that last 100 K miles.

OK, back to sparks:* The obvious reason for a spark is to start a fire in the combustion chamber.* This sounds easy, but can be deceptively difficult to do. In today’s lean engines, the chances that a bit of combustible fuel will find it’s way into the plug gap is increasingly rare.* If the spark were an instantaneous thing, your engine probably wouldn’t run at all.* As we learned in the previous paragraphs, the build up to a spark is a slow process.* The first part of the spark is called the Capacitive part, because the current stored in the metal can be regarded as a capacitor.* Then the energy gradually diminishes until the spark is not as effective.* Then there is a residual part of the spark that can aid in lighting the fire too.* This latter part is the part that causes electrical noise that can be heard in your radio, but can also elongate the duration of a spark to help engines with poor combustion chambers to burn better.* Our beloved EX has a resistor in the plug cap to clip this latter part of the spark. I don’t know why except there must be a Federal Regulation that limits Spurious radiation along with gas emissions.

Ok, if any of you are still awake, I hope you have learned something of use as you think about your motorcycle.* There’s a lot more to this stuff that most mechanics understand, and this is what gives rise to the bad decisions that I read about on this, and many other forums.

[Finesse]

my 650r does this once in awhile. I don't feel like messing with it. let me know what the solution to your problem is and I might do the same thing lol.

[sh123469]

Here's an update on what's going on.

I have removed and gone through the carbs. They were pristine inside. No crud, no discoloration, no marks where anyone had ever been in before.

Diaphrams and slide work great. All jets and passages clean and passing air with no problem. Chokes work as they should and slide is moving freely.

I always use real gas, no alcohol.

I have removed and checked / cleaned the plug caps and wires to the coils. I found nothing wrong there either. Everything looked pristine with dust on the outside of the items.

I did notice that the PO had installed Autolite plugs. According to Advance Auto they are the proper cross reference. I have NEVER had a good Autolite plug. They always cause misfires. I closed the gaps a little on the plugs from the factory specs and it runs better but the miss is still there, just not as bad. I'll be ordering the proper NGK plugs for it soon and see if that fixes the problem.

One other thing I noticed, since this started, I never have to choke it. Before, I always had to choke it to get it started, even if it was 85 deg. In fact, if I choke it now, it usually won't start.

[xXecuterXx2]

Autolite is trash, those NGK's oughta do you nice, keep us posted.

[jkv45]

How about the idle mixture screws - where are those set?

Because you don't need to use choke, it would suggest the idle circuit is adjusted too rich for whatever reason.

[sh123469]

The caps are still on the mixture screws. It was late and I didn't remove them. Wondering why the idle would richen that much. I have always had to choke it when cold starting.

I also noticed something strange. Probably something stupid on my part. Ever since I bought the bike I have gotten 62-63 mpg my last tank was 86 mpg.

I am currently assuming I didn't reset the trip meter when I refuelled or something. I will check mileage again when I empty this tank and see if it's still different. A close to 30% change in fuel economy without any corresponding change in fuel, bike, or riding style just doesn't make sense. Hey, that's just about the time I noticed that the airbox wasn't properly connected to the carbs and reconnected it. Could it make that much difference?

[Ghostt]

If the tamper caps are still on the carburetors, then you couldn't have cleaned the idle circuit.

Did you physical remove the idle and main jets? And main jet holders? Did you verify all the fuel circuits were clear with a air compressor? Set the float height? Etc......

http://faq.ninja250.org/wiki/Changin...rands_to_avoid

NGK Iridium IX® plugs are the way to go personally, I run them in both the Ninjette and EX.
http://www.ngksparkplugs.com/product.../iridiumix.asp

NGK (7669) CR8HIX Iridium IX Spark Plug, Pack of 1 https://www.amazon.com/dp/B000HDF852..._3P6Zvb2PBX9FX

[sh123469]

I removed all jets and verified they were clean, jet holders as well. All circuits flow air just fine. The idle circuits flow air just fine from the jet opening out the little hole. Both sides flow the same. Although much harder to check, they do flow air back to the jet opening as well. You can get a huge amount of air through those main jets even if they are actually quite small. Float needles and seats look great.
Float height was checked according to this http://faq.ninja250.org/wiki/How_do_..._the_floats%3F They are both at exactly 17mm and no fuel in either of the floats.

This isn't my first rodeo with carbs. I've had bikes with carbs for the last 40 years. I've cleaned, adjusted, made jets, rigged, soldered, patched, just about anything you can do with a carb on a bike, I've done it.

Given that everything inside the carbs is pristine, no dust, dirt, goo, rust, discoloration even, jets are open, all passages flow, diaphrams and slides work well, floats and needles are fine, I don't believe there is anything wrong in the carbs.

It feels and acts more like dirty points or a bad condenser on a real ignition system.

If you feel it's imperative that the mixture screws be removed even though the circuits flow the same amount of air in each carb, I'll pull them and do it just to make sure.

I was thinking very seriously about the iridium plugs. I've heard so much good about them and very little bad.

[Ghostt]

I personally remove the idle mixture screws for cleaning, and verify that the fuel circuits are clear with an air compressor, I also replace the O-rings on the idle mixture screws.

Sorry if I misjudged your abilities, but you've seen plenty of posts like this one, from noobs.

[sh123469]

I have and have seen lots of times when something that really should have been done wasn't. That's why I asked if you thought it was imperative, I would do it.

Although I've had lots of experience with carbs, this bike and its carbs are new to me. There can always be a gotcha hidden somewhere.

Any ideas about the fuel economy? I just can't believe that I didn't do something to fudge that calculation somehow. I've never heard of a 30% increase with nothing being done to prompt it. And, a 30% increase is very hard to get no matter what.

I always use the same pump and fill just to the bottom of the little tube in the filler hole. Last fill up was 3.07 gallons and 288 miles on the trip meter. My bad, that figures to 93mpg...no way...I have to have done something wrong like forget to reset the trip meter or something. That kind of mileage outdoes my little 50cc scooter by a good bit.

I haven't noticed any performance difference other than the little misses at around 2500 to 3000. Power is still fine, same pull is still there. No funny noises other than the clutch basket rattle.