# Reading A Used Spark Plug/ Update with Pics



## thewoodlands (Mar 7, 2012)

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

Since I'm changing the spark plugs on the Stihl Chainsaws I thought this was appropriate. 

zap


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## smokinj (Mar 7, 2012)

zapny said:
			
		

> http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp
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> Since I'm changing the spark plugs on the Stihl Chainsaws I thought this was appropriate.
> 
> zap



Good stuff!


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## thewoodlands (Mar 7, 2012)

I take a quick look when taking them out but will pay more attention to what they are saying, the 310 & 390 will get changed tonight then I'll throw the pics up of the old spark plugs.

Zap


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## ScotO (Mar 7, 2012)

Great info there, Zap.  When I tune or rebuild a saw, I use the spark plug as one way to get the saw tuned properly.  Everybody that does serious firewood cutting or logging should know how to watch their spark plug and tune their saw.  Thanks for sharing!


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## Bocefus78 (Mar 7, 2012)

Good info for sure!  I just got done giving the local shop almost $55 for those stupid bosch plugs for all my stihl stuff I clean and keep the old ones as spares in case of failure on a job.


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## HittinSteel (Mar 7, 2012)

Bocefus78 said:
			
		

> Good info for sure!  I just got done giving the local shop almost $55 for those stupid bosch plugs for all my stihl stuff I clean and keep the old ones as spares in case of failure on a job.



Yikes, I'd be scared to death to see the mark up by stihl for a sparkplug........here's a cross reference list if you want to tell your dealer to take a flying leap.


http://www.angelfire.com/extreme4/skidoolympique/SPARK_PLUG_CROSS_REFERENCE.htm


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## thewoodlands (Mar 7, 2012)

Bocefus78 said:
			
		

> Good info for sure!  I just got done giving the local shop almost $55 for those stupid bosch plugs for all my stihl stuff I clean and keep the old ones as spares in case of failure on a job.



Just bought three Bosch plugs for the saws from our local Stihl dealer, cost was $5.00 plus tax.


zap


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## smokinj (Mar 7, 2012)

zapny said:
			
		

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Yea, but he got those ones that gives it extra horse power!  :lol: So 10.00 a plug and you can add another 7 percent to the bottom line. ;-)


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## ScotO (Mar 7, 2012)

smokinjay said:
			
		

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a 40% power increase fer sure  Who needs porting!  Lol....


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## firebroad (Mar 7, 2012)

WoW!  What a great list of info.  I am going to print that out.

$55 spark plugs?!  And to think I yelped at $7...


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## backpack09 (Mar 7, 2012)

I always end up with yellow tips on my plugs.... All that leaded race gas I use.


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## thewoodlands (Mar 8, 2012)

smokinjay said:
			
		

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Pic 4744 is the plug from the 660 and pic 4745 is the plug from the 390.

The spark plug in the 310 was new,the plug from the 390 is the one on the right in picture 4742 and the 660 plug was horrible. Mixing 50-1, the 660 plug was in for all the milling. Is the 660 plug dry & wet fouling or running hot?

zap


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## ScotO (Mar 8, 2012)

That 660 plug looks like it is being run a little rich, leading to dry fouling.  I am assuming you keep it running at high throttle, being you are milling with it.  When you adjust your high throttle screw, is that being done with the air filter cleaned out and installed on the saw?  Sometimes a clogged up air filter can cause your plug to get like that too!  Looking at that plug that's what I would say is going on.  Just a hair too rich...hold 'er at full throttle, tune the high screw down a little and that should clear it up...


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## thewoodlands (Mar 8, 2012)

I posted that my mixture was 50-1, but when I stopped by our local Stihl dealer in late fall he mentioned I would be better off mixing 40-1 so I had about 4 gallons mixed that way, would that cause that?

zap


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## ScotO (Mar 8, 2012)

zapny said:
			
		

> I posted that my mixture was 50-1, but when I stopped by our local Stihl dealer in late fall he mentioned I would be better off mixing 40-1 so I had about 4 gallons mixed that way, would that cause that?
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That could lead to that, absolutely.  When you adjust your oil/fuel ratio, or even changing from one octane to another (or from pump gas to AvGas) you will need to tune your saw to run with the changed mix.


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## thewoodlands (Mar 8, 2012)

I'l go back to 50-1 then just check the plug every so often. The plug I took out of the 660 Stihl was a NGK R BPMR7A, the plug they sold me is a Bosch R 10, is there a conversion chart out there.

zap


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## ScotO (Mar 8, 2012)

zapny said:
			
		

> I'l go back to 50-1 then just check the plug every so often. The plug I took out of the 660 Stihl was a NGK R BPMR7A, the plug they sold me is a Bosch R 10, is there a conversion chart out there.
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> zap


You CAN reuse your plugs, if you clean them properly (media blast), but you need to do it right.  As for the plugs, NGK's are decent plugs but I pick Bosch HANDS-DOWN.  That's all I use in my saws, period.  As for your mix, I personally would run it at the 40:1, your saw will last longer.  Just tune your high idle screw down to where the saw "flutters" a little at full throttle.  Take it to a saw shop if you have to, trust me it's easy to do.  Google it, maybe you can see how it is done on the 'net.  Let me know how you make out.  If I was closer I'd tune it for ya, bud.......


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## Hogwildz (Mar 8, 2012)

Scotty Overkill said:
			
		

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I'm close, when do I get my tuneup? LOL


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## ScotO (Mar 8, 2012)

Hogwildz said:
			
		

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Bring 'er on over and we'll tune it up bro.  Heck, while we're at it, we'll clearcut some of the mountain behind the house!!  ;-)


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## ScotO (Mar 8, 2012)

Zap, here is one cross-reference chart I found.  This isn't all of the saws out there, but this does have some cross-references for many plugs still used today. 

http://www.acresinternet.com/cscc.n...e39d1995d7ddc91588256e0c00029d0f?OpenDocument


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## MasterMech (Mar 8, 2012)

I'm curious what the plugs from saws running AvGas look like... Anybody got a pic?


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## wkpoor (Mar 8, 2012)

MasterMech said:
			
		

> I'm curious what the plugs from saws running AvGas look like... Anybody got a pic?


I've taken pics in the past but don't have any handy right now. They stay pretty darn clean on AvGas which is all I run in all my 2 cycle hand held stuff. I also run it in my Farmall H that has 225 lbs cranking compression. They stay spotless clean in that machine. I would say they have more of a bone color than tan like pump gas.


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## Hogwildz (Mar 8, 2012)

Scotty Overkill said:
			
		

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You gimme the directions, I'll be there.


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## ScotO (Mar 8, 2012)

Hogwildz said:
			
		

> You gimme the directions, I'll be there.


I'm between State College and Altoona.  My one buddy used to work at the Nuke Plant up there in Berwick!!


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## nate379 (Mar 8, 2012)

I generally don't worry too much about plug condition on small engines.  It's seldom I pull out plugs that are "normal".  The little engines are run hard and the carbs are simple and crude compared to even a 30 year old car's carb.


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## ScotO (Mar 8, 2012)

NATE379 said:
			
		

> I generally don't worry too much about plug condition on small engines.  It's seldom I pull out plugs that are "normal".  The little engines are run hard and the carbs are simple and crude compared to even a 30 year old car's carb.


Really?  I guess all those mechanics that say otherwise are wrong......sorry but I disagree.  The condition of that plug tells everything, if you got a dirty carb, your engine isn't running to it's optimum.....


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## thewoodlands (Mar 9, 2012)

Scotty Overkill said:
			
		

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Do you run regular unleaded for gas in your saws?

zap


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## ScotO (Mar 9, 2012)

zapny said:
			
		

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Zap, yes I do.  I run 92 octane in them.  I mix my gas with (drumroll please)......TCW3 oil.  I don't care what anybody says, I have never had an issue and I have a PILE of hours on all my saws, most of the ones I use are 35+ years old and still kickin' ass.  I run a 35:1 mix, saw is tuned to that mix.  Never, ever had a failure either.  Oh I foul the occasional plug, as when you run your saws alot (and I know you run yours quite a bit, too) like I do, you tend to run them with the filter clogged, sometimes forget to turn the "off" switch back to "on" before pulling it 4 or 5 times, cursing and swearing at it (been there, done that!) ,trying to start it when it's already warmed up with the choke button accidentally bumped "on" (that really pi$$es me of).... :lol: There are all kinds of variables in making that plug a little dirty.  But the biggie is not tuning the carb to the mixture.  When I run AvGas in it (occasionally), I have to lean it out a little.  And it does scream with more power with the AvGas, but that gas is not totally necessary.  I will say that when storing the saw for a really long time, you should run it dry (run all the gas out of it) or store it with AvGas throughout the system.  Will be much easier to start, and will not get varnished in the carb like it will if it is stored with this modern junk pump gas in it.


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## amateur cutter (Mar 9, 2012)

modern junk pump gas in it.??????? 

How can it be junk? They're gettin $4.00 a gallon around here lately.  :bug: 
BTW glad to here I'm not the only saw junkie around that re tunes regularly, do you tune for ambient temp also? A C


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## ScotO (Mar 9, 2012)

amateur cutter said:
			
		

> modern junk pump gas in it.???????
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> How can it be junk? They're gettin $4.00 a gallon around here lately.  :bug:
> BTW glad to here I'm not the only saw junkie around that re tunes regularly, do you tune for ambient temp also? A C


yeah, tell me about it.  With pump gas going upwards of six bucks this summer, wonder how much that AvGas is gonna be??  probably around 10 to 11 bucks a gallon....I usually tune it at the beginning of any job we do, just so it's purrin like a kitten......


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## MasterMech (Mar 9, 2012)

Scotty,

That "antique" line-up probably doesn't mind the TCW-3 oils nearly as much as a modern day 14K+ rpm screamer would.  None of them are from the 30wt days tho are they?  I think even the 041's reccomend two-cycle specific oil.


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## nate379 (Mar 9, 2012)

,,


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## nate379 (Mar 9, 2012)

Exactly.  Most carbs on small engines are quite crude in making correct a/f mixtures.  Provided that the user constantly adjusts it for temp, altitude, humidity, etc I suppose it could run perfect.

Point I was making is don't stress out over a plug that isn't book definition of "normal"




			
				Scotty Overkill said:
			
		

> There are all kinds of variables in making that plug a little dirty


t.[/quote]


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## fyrwoodguy (Mar 10, 2012)

MasterMech said:
			
		

> I'm curious what the plugs from saws running AvGas look like... Anybody got a pic?



here's a pic of a 357xpg that's being checked over after it's first tankfull of 100LL av gas and mobil 2t synthetic oil.
   the arrow points to the automatic decopression valve.(that has a high failure rate)


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## ScotO (Mar 10, 2012)

fyrwoodguy said:
			
		

> here's a pic of a 357xpg that's being checked over after it's first tankfull of 100LL av gas and mobil 2t synthetic oil.
> the arrow points to the automatic decopression valve.(that has a high failure rate)


Went you your link, you have a nice shop there, Fyrewoodguy!  I tinker on the side doing the chains, bars and tune-ups.  I have a vintage Stihl collection that I use for cutting on the side.  I'm  not real familiar with the Husky saws, what's your take on that plug in your picture?  Looks like theres some ash on it, and you said that's after one tank of AvGas?


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## clemsonfor (Mar 10, 2012)

OK i have a stihl ms390. All this talk about frequent tuning makes me want to retune mine. I tuned it after a carb rebuild (that wasent necessary, another story) last year and dont remember the steps or the sounds im looking for. I think i need to bump my idle speed up a bit or lean out the mix at idle as it seems to idle low. I also think maybe you hold it wide open and tune the highspeed screw till it starts "2 stroking" or blubbering then back it back in a bit?  Does this sound right?  Jus tpost the correct stihl tune steps (i dotn have a tach).


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## fyrwoodguy (Mar 10, 2012)

Scotty Overkill said:
			
		

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good observation there,scott 
there are 3 types of air filters available.one being a felt airfilter that gabs almost 100% of sawdust & dirt.is washable,but can't get all dirt out+felt goes away w/repeated cleaning.
and 2 that are nylon with 2 micron ratings-80. & 44. the 44 is pictured. i'm assuming the "ash" your referring too-is possibly wood ash that is passing thru the airfilter. the latter 2 are recommended for winter use,and the felt for dusty or summer use. here's that same plug after about 5 gal of av fuel used.


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## ScotO (Mar 11, 2012)

Well the filter thing explains the ash I see.  Tell you what,  you got that saw tuned pretty nice now!  Wish I was closer to your shop, I'd probably be the coffee/donuts guy on Saturday mornings!  Great little business you got there, fyrewoodguy!


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## MasterMech (Mar 12, 2012)

clemsonfor said:
			
		

> OK i have a stihl ms390. All this talk about frequent tuning makes me want to retune mine. I tuned it after a carb rebuild (that wasent necessary, another story) last year and dont remember the steps or the sounds im looking for. I think i need to bump my idle speed up a bit or lean out the mix at idle as it seems to idle low. I also think maybe you hold it wide open and tune the highspeed screw till it starts "2 stroking" or blubbering then back it back in a bit?  Does this sound right?  Jus tpost the correct stihl tune steps (i dotn have a tach).



Best thing for novice tuners is to get a tach, set it to factory specs and listen to what's going on.  Then you can tune by ear once you know what you're listening to.


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## ScotO (Mar 12, 2012)

MasterMech said:
			
		

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that's a good point, MM.


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## thewoodlands (Mar 12, 2012)

Is this the correct way to use the tachometer?

Place the chainsaw on a flat work bench.

2 
Check to see if the spark plug wire is exposed. The spark plug wire is black and is connected to the spark plug. If its not exposed, remove the air filter cover located directly above the carburetor. This will expose the spark plug wire.

Sponsored Links


Turn the tachometer into the on position. Wrap the external lead from the tachometer around the spark plug wire.

4 
Start the engine and let it idle. Check the reading in the idle position. Most chainsaw operate between 2500 to 3000 RPM's. Check your model's service manual for the proper range.

5 
Advance the throttle to the full throttle position. Check the reading. Normal RPM's in the full throttle position are between 11000 to 15000. Check your model's service manual for the correct operating range.


Swampy the Rookie


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## MasterMech (Mar 12, 2012)

It depends on the specific model/type of tach but yes that's generally how it goes.  Some are wireless. ;-)


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## ScotO (Mar 12, 2012)

swampy69 said:
			
		

> Is this the correct way to use the tachometer?
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that's about right, swampy.  The pickup for the tach is a probe that reads out the firing pulses off of the plug wire.  The way I do my saws is start the saw.  Back off (very slowly) the low idle mix screw til the saw starts to rev.  When you hear that revving it is starving for fuel, so advance it around a 1/4 then and check throttle response.  For the full throttle you want to hold the saw wide open.  You want to turn the hi-mix screw in either direction until the saw reaches full rpm.  If you are richening the saw you want to go past the top of the rpm curve and turn the screw (while under full throttle) til the saw starts to "flutter" or "cycle".  You want the saw to do that so you are getting good fuel/lubrication when cutting.  When you plunge into wood and cut, the flutter will go away.  With a little practice and patience you can learn to easily tune your saw on the fly. I've never used a tach before but I could see where it would help someone who has never tuned before as it takes the initial guesswork out of tuning.  You'll eventually be able to do it by ear.


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## thewoodlands (Mar 12, 2012)

Scotty Overkill said:
			
		

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Tachs, are all the tachs the same quality or is one better than the other.

swampy


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## MasterMech (Mar 12, 2012)

swampy69 said:
			
		

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Stihl's EDT Series is very good.  Dunno who makes them for them.  Refresh rate will be the make/break feature.


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## ScotO (Mar 12, 2012)

Forgot to mention in my last post that after you find your idle mix and full throttle mix you will have to play with both screws to balance the carb.  Also, remember do have they air filter cleaned out AND warm the saw up before you try and tune it.  If you don't you'll be re-tuning it sooner than you think!


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## thewoodlands (Mar 12, 2012)

MasterMech said:
			
		

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I just ordered through our local dealer the EDT7, should be in next week.

Thanks
Swampy


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## thewoodlands (Mar 16, 2012)

MasterMech said:


> Stihl's EDT Series is very good. Dunno who makes them for them. Refresh rate will be the make/break feature.


 
Just received a call from our local Stihl dealer, the Tach I ordered is in so I'll pick it up Monday morning.

Swampy


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## MasterMech (Mar 16, 2012)

Suhweeet!  Off to tuning nirvana you go!


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## thewoodlands (Mar 16, 2012)

MasterMech said:


> Suhweeet! Off to tuning nirvana you go!


 
I'll do the 310 first, the low idle was off some before I adjusted it. Starting tomorrow the pine is coming out of the woods to be stacked, once that is done I might start milling.

swampy


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## ScotO (Mar 16, 2012)

Let me know how that works for ya swampy.......I looked for a good video link on tuning but most of them were filmed by some really screwy people.  If I find a good video I'll make sure I send it your way.


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## thewoodlands (Mar 16, 2012)

Scotty Overkill said:


> Let me know how that works for ya swampy.......I looked for a good video link on tuning but most of them were filmed by some really screwy people. If I find a good video I'll make sure I send it your way.


Will do SO. I was just reading the 660 manual it says the hi rpm's should be set at 9500, the low idle at 2500.

swampy


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## MasterMech (Mar 17, 2012)

Take those specs with a grain of salt Zap.  I'd take some baseline numbers before you change anything.  Adjust to spec, but if the saw still doesn't sound/run right, don't be afraid to tune "outside the box" a little.


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## ScotO (Mar 17, 2012)

MasterMech said:


> Take those specs with a grain of salt Zap.  I'd take some baseline numbers before you change anything.  Adjust to spec, but if the saw still doesn't sound/run right, don't be afraid to tune "outside the box" a little.


a big +1 to that, MM.  Swampy, those factory specs are a baseline.  Altitude, temp and humidity,  etc. play a factor in tuning as well.  Don't be afraid to let your ear do some of the tuning.   You'll get it figured out.  We'll be here for support.


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