Fouling

Yeah, they come jetted piss-rich from the factory. Wait to until you break it in before fooling with the jetting.

However, with that said raise the clip one position on the needle. I say this because you mention that it's rough at 1/4 throttle and that's where you start to get into the needle. This should keep you from fouling plugs. The KDX motors usually don't foul the plug (unless the jetting isn't even close) on the pilot jet.

When you get in broke-in, check the FAQ for additional information opn jetting. Enjoy your new purchase.

To adjust the clip, you just take the cap off the top of the carb, and then slide out the slide which has the needle in it. Then you usually disconnect the slide from the cable and then can take out the needle, then raise the position of the clip one notch up, therefore lowering the needle when seated in the slide and making the bike run a little leaner.

Yeah you can raise the needle with carb on bike. Loosen clamps and tilt carb to get to it. Unscrew top piece on carb....pull it out slowly and you will find the needle. I had same prob as you and finally went with a BR8EG plug. The "EG" series is the key. No fouling. A BR7ES will not foul but may be a tad too hot. A BR9ES is colder...not hotter. Don't try it. Since your in Knoxville you must go check out Coal Creek/Windrock Mountain riding area in Oliver Springs. Awesome trails!

Oh, some more newbie advise, use needle-nose pliers to remove the clip and hold on tight. Those things always have a way of flying off and embedding themselves into someplace you can't get to.

All my previous bikes ran fine with a 32:1 mixture but not my kdx. It fouled out every 50 miles or so also. went to 42:1 and it got better. Now 2 years later I run at 50:1 with a synthetic and have no problems and no excessive wear after my first top end job which had 2 seasons on it. Toss the top lid except for washing the bike.

If you have not all ready, go read C.Daves Carb tuning in Tech Tips. Then read it again, and again, and again. It starts getting clearer and clearer...

a KDX which is jetted properly shouldn't foul plugs even with 24:1 mix ratio. Some brands/types of oil contribute to fouling, but with the right jetting it really shouldn't be an issue. At 50:1 maybe the piston is ok but the bearings would probably prefer more oil in the mix.

the pilot jet and air screw have a significant effect on fouling because every time you let off the gas, if the mixture is rich the engine starts loading up. Try turning the air screw out 1/2 turn at a time until you notice hesitation, then turn it back in a bit. If you end up over about 2 1/2 turns out you need a leaner (smaller) pilot jet.

The search function appears to be back (I just used it, anyway). Do some ...searching that is.

The 'Every kdx rider should read...' at the top of this forum us a must for you to check out.

No-one can tell you how to jet. The basics, maybe, but not 'this number, that number.' Jetting varies too much by rider to do that.

Read this:

http://www.dirtrider.net/forums3/showthread.php?s=&threadid=48348

When you put the throttle cable back in the needle retainer nut, make sure the white nylon piece on the assy has it's protruding key properly placed in the nut slot. Easy to miss it.

Some never seize on the nut is a good idea.

BTW...use the proper socket on the nut. 6mm I recall? Same as the size for the main jet. Don't use pliers or an adjustable wrench unless you have a spare piece handy. They crush fairly easily.

The 'g' series ngk plug is a fine wire electrode. A great plug! Whether your choice is the 'g' series or the even finer wire irridium plug, you will get much better performance (reliable spark on less than perfect conditions) than from the standard nickel 'es' plug.

Check ngk's website for all you need to know about the different plug series.

As braahp said...the 7 is one step hotter. Not a substitute for proper jetting. It will raise the engine temp 50-80º. An ngk tech told me they chose the '8' for the kdx (later 'h' models) for a reason.....cuz it's the right plug!

BTW...CDave's site (noted above) has a 'new bike prep' section that you should read. Failure to properly grease some vital components in your new bike will lead to premature failure.

Have fun!

great post canyn, but I believe you mean to say that the hotter plug tuns 50-80 degrees hotter on the tip of the plug...the engine runs the same regardless.

the heat range is simply a measure of the heat conduction characteristics between the tip of the electrode and the cylinder head. A hotter plug will burn off more of the goo (thus less fouling) but will also burn a piston more easilly if you run it hard enough with a "hot" plug.

No, I mean to say what I said.

Directly from NGK (and some other places). I haven't measured it myself ;), but engine temp does indeed change with the heat sinking (or not) ability of the plug.

Want some links that say so?

sure, link away, i'm always open to learning more info on thermodynamics.

if anything, the head should run a bit HOTTER with a "colder" plug, because a colder plug transferrs more heat away from the tip, but that's a stretch (cooling systems on modern bikes are very efficient)

also, 50-80 degrees is A LOT! that would mean if we were already running 170 we would now be at 220-250...I don't think so...

From: NGK

'SPARK PLUG BASICS:
The spark plug has two primary functions:

*To ignite the air/fuel mixture
*To remove heat from the combustion chamber' (my emphasis)


......and

'It is important to remember that spark plugs do not create heat, they can only remove heat. The spark plug works as a heat exchanger by pulling unwanted thermal energy away from the combustion chamber, and transferring the heat to the engine's cooling system. The heat range is defined as a plug's ability to dissipate heat.'

...and

'...the heat range is a measure of the spark plug's ability to remove heat from the combustion chamber.'

...and

'In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C'

+++++++++++++++++++

In every reference to 'removing' heat, where would you suppose that heat 'goes'? And, you're right. 50-80º is indeed a lot of hot. NOT as much as 70-100º..........centigrade, 'eh? I misremembered that part. Actually, did think it was 70-100ºC, but thought...wow! That's a LOT of heat!! ;)

+++++++++++++++++++

Of less validity maybe, there's this:

'The spark plug works as a heat exchanger by pulling unwanted thermal energy from the combustion chamber and transferring heat to the engines cooling system.'

From: Here

'The secondary (and most overlooked) function of the spark plug is to provide a reliable path for the heat generated by the explosion of the air-fuel mixture to be dissipated. Average exhaust temperatures occur in the 1,100 to 1,350 degrees Fahrenheit range. Taking into consideration that at the point of explosion of the air-fuel mixture, temperatures of 3,800 to 4,500 degrees Fahrenheit can be generated, the difference is dissipated into the engine cooling system. Since the melting point of nickel alloy is 2,200 to 2,400 degrees Fahrenheit, it can be readily seen that temperature can be a major factor in the performance of the spark plug. The major path of this heat dissipation (in a water cooled engine) is through the spark plug (from spark plug center electrode tip, to the ceramic insulator, to the shell, to the engine head, to the water jacket).'

+++++++++++++++++++++

Besides all this, there's the common sense approach. A 'hotter' range plug sticks out further, is subject to more heat, gets hotter (than a colder range plug). The plug will then heat up whatever it's touching. It doesn't get hot all by itself to no co-incident effect! How could that be? Maybe if the plug was isolated/insulated somehow...but it's not. Being screwed into the head and thus 'contacting' the water jacket, as the plug gets hotter, so will they!


One more here:


'It is also important to remember that spark plugs do not produce heat. They pick up heat from the combustion chamber and move it to the cooling system.'


++++++++++++++++++++

This only took me 45 minutes. I'd guess that google works as well for anyone else as it does for me. This time I'll save the whole mess so that next time it comes up (this isn't the first time) I can just copy-'n-paste the whole shebang!

Cheers!

very interesting topic, lots of thermodynamics at work here. I believe (with the 70-100 degrees C) they are referring to elevation of temperature of the plug tip, not the head. Also, keep in mind that one degree C = exactly 1.8 degrees F. Due to the huge variety of engines and cooling systems, any increase in actual head temp couldn't be accurately calculated. Consider an air cooled engine with minimal cooling fin area vs. a liquid cooled engine with a powerful cooling system.

Gotta go ride, maybe i'll be back on later tonight :thumb:

Also, keep in mind that one degree C = exactly 1.8 degrees F

Click to expand...

I don't know what you are thinking there??

O* C = 32*F :thumb:

no, silly, not literally "one degree", maybe I should have worded that better...each degree C is equal to 1.8 degrees F. We were speaking about a differnential in temperature, not absolute temperature.

If you want to convert C to F take it times 1.8, but then add 32. So, 0 C = 32 F, etc.

If a single heat range colder plug removes up to 100 degrees C from the cylinder temp., and my bike only heats up to 180 degrees F or 82 C anyway, then if I use a B9ES my bike will be running below freezing???!!!! I know that isn't right. so if I drop the plug from B8ES to a B9ES what can I expect my engine temp. to drop by?

1000º Kelvin! ;)

You missed the point. Temps inside the combustion chamber can be (listed by ngk) 3800-4500º. That's what the temp diff is related to. That's what the plug is sinking heat from!

Obviously, the temp diff noted by ngk by a heat range number has no direct relationship numberwise to coolant temp.

Specifically, the temp change in coolant by a heat range change? Howabout...I dunno. 'Less' in the case of a cooler plug, 'More' in the case of a hotter plug.

In Eric Gorr's book he states each step in a heat range will increase the EXHAUST GAS TEMP, by 50 degrees. That going from a 9 to a 8 range plug.
I have ran a b7es plugs in my RMX 250 with no ill effects on the motor.
If I'm going to be setting up trail or just poking along I will run a 7 in the RMX.

Can you put a quote to that effect here?

Now that''s precise! Now I've got a new project, I'm going to buy a couple of plugs, one range hotter and one cooler, take the bike out with the B8ES and measure, change to the 9, measure, change to the 7 and measure. I will report back my findings. Any guesses on the outcome? I love experimenting, especially when I get to play with fire.

Have fun....but any 'result' will likely matter not a whit.

Things like load, fuel, atmospheric conditions (sun spots?) will have a HUGE impact on any temperature readings.

Even fairly controlled events as doing the same thing twice with two different plugs on the same day won't be the same....cuz one of 'em has to take place first!

Have fun anyway!