Spark plug heat range question.

['03KDX200]

First of all, wow that made a big difference! I went from a BR8ES to a BR7ES, and jeese I was surprised how big of a difference that made. I'm riding about 3500ft and 45 degrees F ambient temperature. The bike started in one kick and immediately idled so high that I had to back off the idle speed adjustment a lot. I couldn't believe the difference. It felt like it gave the bike about 10% more power all through the rev range, and also created a nice linear pull, not full of little steps in the power output as the bike pulls. I was amazed at the difference.

Anyways, what's your opinion of how hot of a plug I should use? Should I experiment with one or two ranges even hotter? Is there a point where it doesn't make a difference? Is there a risk of melting my piston if I go a plug or two hotter?

[Goat]

Very interesting!
My only experience comment is my bike came with B9 and going to B8 cleaned up the plug bit. I could not tell a difference in how it ran.
Googleator does recommend on step hotter plug above 3,000’. But that should use primarily carb mixture and timing to compensate for elevation.
Hope someone else is more expert.

[SS109]

I've never heard of someone running a BR7ES in the KDX. It's just not needed if everything is in proper working order and jetted correctly. I would bet you're either pretty rich now or pushing closer to the edge of detonation. Too hot a plug can lead to piston meltdown so be cautious and read what your plug is telling you.

['03KDX200]

I've never heard of someone running a BR7ES in the KDX. It's just not needed if everything is in proper working order and jetted correctly. I would bet you're either pretty rich now or pushing closer to the edge of detonation. Too hot a plug can lead to piston meltdown so be cautious and read what your plug is telling you.

You've never heard of someone using a different heat range plug???? That's surprising to me, considering how awesome an improvement it was. Try it, you'll like it. I mean why would they make different heat ranges of plugs at all then? If heat ranges of plugs is a legitimate tuning technique, then yeah I would imagine you can experiment with a hotter plug when we're talking about a 40F degree day versus a 100F degree day.

I have one of those aftermarket radiator caps with the temperature gauge built in, so I can closely monitor my engine coolant temperature. I watch it like a hawk during all types of situations, and the temperature of this bike seems totally unchanged before and after going to the BR7ES plug. That is, I watch it after a long, slow first gear uphill climb, after long, wide open high-speed blasts, everything. Temps go up and down but doesn't seem to be any different than when I had the BR8ES in there. So it would appear I have even more wiggle room for a plug that is hotter still.

(Edit: After some technical reading online I found out that one hotter plug range will raise the internal cylinder combustion gas temps by around 200F, yet won't raise the temp of the coolant very much. The extra heat goes right out the cylinder before it can be absorbed by the cylinder head. This means that measuring coolant temperature is actually an unreliable way to predict when you're going to see pre-ignition problems.)

I guess I'm looking for someone who has actually melted their piston from a too-hot plug, and what the conditions were like in that scenario.

My jetting is almost spot-on. Like I said it's a brand new RB Designs carb, and then I've swapped out main jets and pilot jets and adjusted the air screw until everything is as perfect as you can get in terms of throttle response at all different combinations of throttle openings and RPM ranges. Boy this engine is really a thing of beauty when you get everything dialed-in, my goodness!!! I think I'm going to go richer on my pilot jet actually, because this plug looks a little lean. The insulator is mostly white instead of a nice tan color, and my air screw is on full-rich setting (screwed all the way in).

(edit: further down in this thread I swap both pilot and main jets to larger sizes and talk about the difference)

Just for reference, I'm attaching a picture of both my hotter BR7ES spark plug after about 3 hours of mixed riding, and a picture of the BR8ES after 10 hours of mixed riding. Note: Both pictures were taken with the same exact carburetor jetting. The plug on the BR7 gives me mixed signals though I would say, because the insulator looks like it's running lean to me, while the end of the threads are black with unburnt oil. Is this normal on a 2-stroke?

Here's another detail: Both plugs were burning regular 2-stroke oil, nothing fancy like synthetic or smokeless 2-stroke oil. That may be why it's so black around the end of the threads with unburnt oil. My next batch of fuel is going to be fancier, synthetic "smokeless" 2-stroke oil.

Does anyone have a favorite, cheap 2-stroke oil that leaves a minimum of black oily deposits in the cylinder? The less black gunk the less often I'll need to clean the KIPS system too ;)

BR7ES Spark Plug after 3 hours in the KDX 200.jpg (319.73 KiB) Viewed 2755 times

10 hours on the BR8ES spark plug for KDX 200 (same jetting).jpg (434.53 KiB) Viewed 2682 times

[Molly's 70]

Respectfully, Something sounds wrong. You say your "air screw" is seated all the way in? If it were me, I'd go back thought the jetting guide. I know all bikes are different, but something just does not sound right.

[SS109]

I've never heard of someone running a BR7ES in the KDX. It's just not needed if everything is in proper working order and jetted correctly. I would bet you're either pretty rich now or pushing closer to the edge of detonation. Too hot a plug can lead to piston meltdown so be cautious and read what your plug is telling you.

You've never heard of someone using a different heat range plug???? That's surprising to me, considering how awesome an improvement it was. Try it, you'll like it. I mean why would they make different heat ranges of plugs at all then? If heat ranges of plugs is a legitimate tuning technique, then yeah I would imagine you can experiment with a hotter plug when we're talking about a 40F degree day versus a 100F degree day.

I have one of those aftermarket radiator caps with the temperature gauge built in, so I can closely monitor my engine coolant temperature. I watch it like a hawk during all types of situations, and the temperature of this bike seems totally unchanged before and after going to the BR7ES plug. That is, I watch it after a long, slow first gear uphill climb, after long, wide open high-speed blasts, everything. Temps go up and down but doesn't seem to be any different than when I had the BR8ES in there. So it would appear I have even more wiggle room for a plug that is hotter still.

I guess I'm looking for someone who has actually melted their piston from a too-hot plug, and what the conditions were like in that scenario.

My jetting is almost spot-on. Like I said it's a brand new RB Designs carb, and then I've swapped out main jets and pilot jets and adjusted the air screw until everything is as perfect as you can get in terms of throttle response at all different combinations of throttle openings and RPM ranges. Boy this engine is really a thing of beauty when you get everything dialed-in, my goodness!!! I think I'm going to go richer on my pilot jet actually, because this plug looks a little lean. The insulator is mostly white instead of a nice tan color, and my air screw is on full-rich setting (screwed all the way in).

Just for reference, I'm attaching a picture of my BR7ES spark plug after about 3 hours of mixed riding. The plug gives me mixed signals though I would say, because the insulator looks like it's running lean to me, while the end of the threads are black with unburnt oil. Is this normal on a 2-stroke?

BR7ES Spark Plug after 3 hours in the KDX 200.jpg

Different heat ranges are for various engine designs and for special tuning situations. The KDX is not one of them IMO/IME. In all my years I've never heard of the KDX, 200 or 220, liking or wanting a 7 series plug.

Just an FYI, bikes run really crisp and powerful running lean right up until you melt a piston. That plug shows you are on the lean side but at least it isn't pure white.

[KDXGarage]

That plug is too hot!! PLEASE put an 8 in there ASAP.

PLEASE look up proper spark plug temperature pictures. Don't look at car spark plug pictures, but two-stroke dirt bike plugs. It should be a light chocolate tan.

['03KDX200]

Respectfully, Something sounds wrong. You say your "air screw" is seated all the way in? If it were me, I'd go back thought the jetting guide. I know all bikes are different, but something just does not sound right.

Thank you. You're right. Actually since this picture of my spark plug was taken I went two steps richer on my pilot jet and one richer on the main jet. I'm now at a size 50 pilot jet and a 160 main jet. Now I finally feel the engine is jetted absolutely perfectly, because the "second sweet spot" for my air screw while riding is at 1.5 turns out. Now it's nothing but smooth, linear power delivery from below idle speed all the way up. ...Well there's a nice little "on the pipe" feeling that starts in the upper midrange but besides that there's no more steps in power output. No bogging, no hesitation at any throttle opening at any RPM. And just for reference in case anyone is wondering, my elevation is about 3300 feet, and average daytime high of 45 degrees F.

I think I'm finally feeling the way this engine is supposed to be. It aught to be, damn it, with a brand new $380 RB-modded carburetor and a COMPLETE (upper and lower) engine rebuild by a reputable motorcycle shop here in town. Even then it took me about 15 hours of riding and fiddling to get to this state of perfect tune (I added an engine hour meter).

[SS109]

I'm really shocked you are that far from RB's recommended jetting. I'm at 2000ft and run a 152 main and a 38 pilot.

[KDXGarage]

He might have water in the air, unlike your moonscape you ride on. LOL

['03KDX200]

He might have water in the air, unlike your moonscape you ride on. LOL

LOL moonscape!

['03KDX200]

I'm really shocked you are that far from RB's recommended jetting. I'm at 2000ft and run a 152 main and a 38 pilot.

I was really surprised at this too. Honestly I was careful and not hasty, taking my time, researching, following that excellent jetting guide here on KDXrider.net (viewtopic.php?t=1156) and I went up one jet at a time, and it took a long time (15 engine hours) because I wanted to be sure I wasn't being an idiot about jetting. But yeah honestly the carburetor as-delivered from RB Designs was giving me that lean bogging crap all the time, and taking forever to warm up. I also bought an aftermarket air screw from JD Jetting and an aftermarket idle speed screw so I could fiddle without using tools. It came from RB with a 42 pilot and a 152 main, so 50 and 160 is pretty surprising, especially for 3300 ft above sea level. I blame it on the cold weather and probably 50% humidity.

[SS109]

He might have water in the air, unlike your moonscape you ride on. LOL

So true. LOL!

['03KDX200]

That plug is too hot!! PLEASE put an 8 in there ASAP.

PLEASE look up proper spark plug temperature pictures. Don't look at car spark plug pictures, but two-stroke dirt bike plugs. It should be a light chocolate tan.

Thanks for looking out for me KDXgarage, but I've got to experiment at least a few more engine hours and do some more tests with this hotter spark plug. Wish me luck my friend. I choose to boldly go where few men dare to travel. And I have to fill my brain with the data that it's thirsty for, while everything is working and running properly.

Speaking of which, I did spend quite a while on the web earlier today, doing Google image searches, trying to specifically look for 2-stroke spark plug condition chart. Couldn't really find one. If you have a 2-stroke-specific plug chart image/link, I'd love to take a gander at it.

Oh here's another 2-stroke spark plug heat range question real quick: It's about detonation. If you're riding a 2-stroke and for whatever reason the engine starts detonating here and there, how obvious is it? For instance do you normally feel a little jolt go through the bike/powertrain? I would guess that you could hear it and feel it when it pings/preignitions/detonates.

[KDXGarage]

With your huge edit of a "two days ago" post, you gave turned this thread into a bit of a bad movie, with all the time jumps back and forth.

If anyone new jumps in, they are going to be wondering why people responded how they did in the posts after your post that have now edited 8 times. :-)

Which exact oil are you using? What gasoline?

The plug should be tan. It may change color with a new plug and different oil.

As to pinging, if it's bad, one can hear it.

['03KDX200]

With your huge edit of a "two days ago" post, you gave turned this thread into a bit of a bad movie, with all the time jumps back and forth.

If anyone new jumps in, they are going to be wondering why people responded how they did in the posts after your post that have now edited 8 times. :-)

Which exact oil are you using? What gasoline?

The plug should be tan. It may change color with a new plug and different oil.

As to pinging, if it's bad, one can hear it.

Ha, I know sorry about all the edits, but it seems bad to lead people down a potential rabbithole if I leave it to them to have to read the whole thread before they arrive at the right conclusion at the bottom, eventually. Seems nicer to the reader to give them a heads-up on what some conclusions were up front, especially if they directly contradict my original post. And yes you're right; I'm trying to achieve the same effect on the reader as when watching that movie Memento, with super-confusing time jumps baked in

As to the 2-stroke oil I was using for pre-mix, I think it was something like Ace Hardware 2-stroke Oil. Was nice and cheap though! When writing about the new fancy oil I got, I'll make sure to mention the brand and exact name.

The gas I was using during all this testing was ethanol-free premium. I'm going to switch to regular premium fuel though pretty soon, because I don't feel like paying double the price for gas for 3% more power.

I will try to get to a nice tan on the spark plug insulator nose. Do two-strokes pretty much always have black carbon deposits on the tip of the threads, around the insulator though? Seems like all the pictures I see online pretty much look like that. Black-and-dripping though, seems bad/unnecessary no matter what.

[Molly's 70]

If it were me, I'd try a bottle of this. https://www.amsoil.com/p/dominator-synt ... g-oil-tdr/ or https://www.amsoil.com/p/interceptor-sy ... e-oil-ait/ mix 50:1.

[KDXGarage]

I think the little oil ring is pretty common, just the way things go.

The cheapest oil is not always the bestest oil.

[SS109]

A good affordable oil is Lucas semi-synthetic. It can be found at a lot of auto parts stores and is right at $10 a quart. I run it at 40:1 (approved for 50:1) and my bike runs clean with a nice tan spark plug. Just a heads up, pick a ratio and stick to it. All of your jetting is affected if you change oil ratios.

[John_S]

I'm having the opposite affect on my plug after 5 hours. The bike runs excellent (without any lean bogs) and the porcelain is a nice tan all the way down but the top of that ring is shiny new looking. The max coolant reading after a few days of lugging a gear high in deep sand twisty trails was 189. I'm used to that ring being dark and don't know what to think.