Help on plug reading...

[MtnEX]

OK... so I don't seem to have much luck on getting color soon enough on my jetting/plug runs.

So I go out and do some general riding and look at plug condition again after that.


The outer part of the center electrode looks pretty darn white. Deeper inside it's dry black... and so is the base ring around at the bottom of the threads.


Should I go down one more main jet size?

[jcs003]

you need to do a WOT plug chop to determine top end jetting. this may also help:

http://www.atvriders.com/articles/sparkplug.html

[MtnEX]

Originally posted by jcs003
you need to do a WOT plug chop to determine top end jetting. this may also help:

http://www.atvriders.com/articles/sparkplug.html

That is just the thing... I can't seem to find enough room to do a WOT run that is long enough to produce color on a fresh plug.

(maybe if I cut the threads off and read the base ring)

I also let it idle with a 42 pilot jet while trying to adjust the fuel screw until it got so hot I couldn't fool with it anymore. Fresh plug had no color.

The only time I get color is just checking after a normal ride.... or if I ride it around on the needle a long time.

Then the tip of the porcelain that is exposed is clean white, while deeper in it is dry black, and so is the base ring.

I thought about moving the needle clip but haven't done it.

[MtnEX]

Oh, and I have no popping or backfiring or anything.

All I have is an occasional "stumble" if I give the throttle just a little rapp from idle. Like if I give it a quick blip from idle to the needle... let's say idle to 1/4-1/3 throttle.

[jcs003]

if it stumbles off idle(slow jet) then it is rich in the pilot. but plug chop refers to actually chopping the plug to see the inside of the porcelin.

this kind of thing is why i switched to a lectron carb. i can adjust the low-mid in minutes. never have to take the carb off or anything like that. its expensive but definitly worth it in performance and convience.

[MtnEX]

What are you actually chopping the plugs with?

And do you pay no attention to anything else about the plug condition?


I'm guessing I need to go IN from 2 1/2 turns out on the fuel screw in hopes I can keep the 42 pilot?

And I am guessing I "may" be rich on the main still, but would need to go in on the fuel screw and check the plug condition visually like I have been? And if I still have black on the plug, try dropping to a 150 main?

As I am guessing actually chopping the plugs will tell me I am rich also since I can see it is black way up after general riding without chopping, and the base ring is black as well.

I had just assumed since the 155 was rich and 148 was stock that 152 would be money...

[Wheelie]

IMO--Don't tune entirely by plug reading, you are throwing all your eggs in one basket.

Tune the bike by how it actually runs, starts, and throttle response and maybe check the plug from time to time for kicks.


I've never done a plug chop in my life, I've checked the plug more times while setting timing than I ever have for jetting.

[Wheelie]

What are your mods, I see some in your sig--what's your elevation and is the lid on or off?

[MtnEX]

Originally posted by Wheelie
What are your mods, I see some in your sig--what's your elevation and is the lid on or off?

Yoshi full exhaust, K&N filter.
I can go either way with the lid... usually on though.

Elevation is 1200 ft.

[Wheelie]

Lid on or off, pick one and tune for it, otherwise you'll never get it right.


Assuming lid on, I'd recommend a 40 pilot, 150 or 152 main. Needle in stock position.

Lid off, 40 pilot and 155/158 main. Needle one clip lower than stock.

[Wheelie]

42 pilot is too much for ANY internally stock EX with the stock carb. It may start great when cold, but off idle performance will suffer once it warms up.

[MtnEX]

Originally posted by Wheelie
42 pilot is too much for ANY internally stock EX with the stock carb. It may start great when cold, but off idle performance will suffer once it warms up.

I was afraid of that... I came really close to getting a 40 pilot instead despite how popular the 42 pilot seems to be.

[MtnEX]

Originally posted by Wheelie
Lid on or off, pick one and tune for it, otherwise you'll never get it right.


Assuming lid on, I'd recommend a 40 pilot, 150 or 152 main. Needle in stock position.

Lid off, 40 pilot and 155/158 main. Needle one clip lower than stock.


I prefer lid on most of the time, just for protection.


When they did the exhaust and filter they left the pilot stock and put in a 155 main. Seemed rich and didn't start well.

So I did the 42 pilot and 152 main.

I guess I could run it with the lid off and see if it's any better. But I am thinking I will have to go to a 40 pilot and 150 main. I just expected it would need more than one size up for the filter and exhaust.