correct plug?

[michael181]

I got a 96 rm250 with a big bore so now its a 265. Should I use a hotter plug?

 

[KX_OUTLAW]

You should put a new one in and ride it to test the jetting.
When you do a wot high speed throttle chop, check the location of the heat mark on the ground strap.

 

[_JOE_]

Your spark plug is the only one who'll know for sure....

 

[julien_d]

Unless the plug were to tell someone.....

 

[michael181]

what do you mean high speed throttle chop

 

[KX_OUTLAW]

what do you mean high speed throttle chop

Go somewhere where you can hold it at wot in 6th gear preferably under light load for 40 to 60 seconds.

Get it warmed up to temp. Put a brand new plug in it.
Go right to wot, full speed, 60 seconds, pull the clutch in and let off the throttle and hit the kill switch all at the same time. Take the plug out and put the old one back in, What you'll be looking for is the hot spot on the ground strap and the color ring around the base of the center electrode (way up inside the plug).

The color of the ring will tell you if it's rich or lean, if it's excessively one or the other you might want to get the main jet right before shooting for heat range.

Big bore kits might need some jetting tweaks.

 

[whenfoxforks-ruled]

Personally, long enough to clear the engine out, hold it and kill it. It only takes a few seconds to get a plug reading. It may not be as dramatic as a year, but it will be true. Reading the ground strap and the color of the porcelain will tell you the timing, and give you an idea of the temperature. But, a lot of variables are in there, like the way you ride it. Not to mention your bike is personal. If its interpreted properly. Its not science, reading the main is. http://www.dirtrider.net/forums3/showthread.php?t=92818 , http://www.dirtrider.net/forums3/showthread.php?t=48348 , http://www.dirtrider.net/forums3/showthread.php?t=108727 . Vintage Bob