Running a B8EGV in 1998 Yz125

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#1
I currently run a BR9ES becuase i have a leftover box of them, and plan on going to the manufactureres recommended BR9EG. The engine is at stock bore, wiseco pro-lite piston, hotrods crank, wiseco clutch basket, stock compression. Vforce3 reeds which i had to modify, and modify my intake boot along with it, so the intake is about an 1/8 of an inch bigger.

I was wondering if it would be good to run a competition NGK B8EGV in it? Should those only be ran in 250's?
 

Rich Rohrich

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#3
Yz250JdT250 said:
I was wondering if it would be good to run a competition NGK B8EGV in it? Should those only be ran in 250's?
It will depend on how hard you run it. Most riders (other than dune or desert riders) I've seen don't run their 125s hard enough for a long enough period to need a 9 series plug. For most of them running an 8 series plug is an advantage.

You don't have to guess because the plug is a very good indicator of heat in the engine, so if the 8 is too hot for your riding it will show up on the ceramic. The ceramic will look like a glazed donut with a weird shine if it's running too hot.

Take a look at this thread for some additional info on heat range and reading plugs.

http://dirtrider.net/forums3/showthread.php?t=92818
 
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#4
So the 9 series is a cooler plug? and 8 is a little hotter? I'm just going by what Yamaha said, which was to run a 9eg.


I have never raced before, i go to tracks and to practice days, and do trail riding. So i'd say that the 8 would help, according to what you said :nod:
 
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#5
Do you know what the effect of my intake being bigger has on the engine? Becuase when i got the Vforce3 reed valve, it didnt line to with the intake boot porting, so i ported the boot and the reed cage myself. The exhaust is the same as before. I brought the main jet up to 150 and left it there, it runs good around here in southern NH. I went riding up north in Berlin, near canada, and it ran so good :)
 

Rich Rohrich

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#6
Yz250JdT250 said:
I have never raced before, i go to tracks and to practice days, and do trail riding. So i'd say that the 8 would help, according to what you said :nod:
I would definitely try the 8. The mods you've done to the engine won't impact the heat range requirement to any significant degree.
 
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#7
Ok, and if the insulator is glazed then the plug is too hot? I was in that other topic and am now aware of that ring, and im going to throw one of the BR9Es plugs in my lathe an see what that ring looks like. So it should be a decent sized ring, and a tan color?

Also, do you know how the bigger intake i mentioned would impact the motor and how i can tune it to get the most juice?

BTW i appreciate you taking time to help me out with this, and im glad that you responded instead of some random person like me. ;)
 

Rich Rohrich

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#8
Yz250JdT250 said:
Ok, and if the insulator is glazed then the plug is too hot? I was in that other topic and am now aware of that ring, and im going to throw one of the BR9Es plugs in my lathe an see what that ring looks like. So it should be a decent sized ring, and a tan color?
When the heat range is correct the insulator should be closer to white. It should look a lot like a new plug, when it's spot on.

As for the tuning, you'll just have to test and change the jetting till you get it right.

Here's a good place to start:

http://justkdx.dirtrider.net/carbtuning.html
http://justkdx.dirtrider.net/carbtuning.html