Spark Plug Reading Picture

[MN250R]

Does this look like a good color for the plug?

Im running a new mikuni stock carb. VM series if i recall. 330 main jet, needle raised as high as it will go.
Machine is SCARY fast. Just a very slight break up at full throttle. ( Im talking when its pinned in every gear) I tried a 300 main jet and the break up went away. But I figured id put in the 330 since i never keep it pinned like that anyhow for a long period of time. I believe it would be better to be a little on the rich side. This is the plug color after running it with a 330 main, and needle raised as high as it will go.


[IMG=http://img163.imageshack.us/img163/1681/img388.jpg][/IMG]

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[RIDE-RED 250r]

Looks safely on the rich side to me. If it performs well with the jetting you have I would stick with it. I'm not sure on how the Mikuni sizes progress, but if there is a size that is between the 330 and 300 you tried (I'm sure there is) try going just one step leaner than 330. Just enough to get rid of your slight burble at top end. I like to run a little on the rich side myself.

[oscarmayer]

what is the plug Gap? if running performance, you shoudl be much tigher than stock. if stock is .028, ru a .022-.020 This will ensure everythign is workig under more pressure. it coudl be a simple case of spark being blown off due to gapping issues. (seen it lot sof times and usualyl occures at the very top) plug looks good, except i seen a slight bit of leaning at the top. the peedle only affects low and part mid. when you it, the needle setting does nothing. I'd increase 1-2 jet sizes and lower the needle to the middle. Again also ensure your gap is set to what I specified eariler.

good luck and use a NEW plug each time you run a test to ensure it's doing what it should. the dark is from rich low and then it burns off as you rip into it. that's what your seeing ont he plug. so adjsut the a/f screw in a slight bit so it's not running so rich down low.

[MN250R]

i have the gap set factory at. 28. so your thinking i should go up a few sizes to like 350. and raise the needle.

also... the temp was 80 degrees yesterday in mn if you can believe that. lol for march.. thats what i jetted it to
...

[oscarmayer]

yea, lower the gap to like .024 for a start.

set the needle in the center and go up a jet or 2 in size.

[1984 honda 200s]

My plug is like this at idle but lean at wot?

[Dirtcrasher]

The actual chart should or must be a "sticky!" somewhere........

[MN250R]

thx. ill give it a try