Reading plugs

[dads400ex]

OK after repiping the quad and putting on the air filter and moding the air box and rejetting and riding at the dunes this weekend I thought I new how to read plugs but now I am not sure, when looking at the plug are you checking the insulator around the electrode or what? As mine was a lite brown around that insulator but black sooty looking around the threads and the quad ran good from bottom to top.

What do you all think,
dads400ex

[oynot400]

If the insulator is brown I would call it good. But if you want to check it put in a new plug, that way you get a fresh reading. ;)
For a quicker readings look at the electode, there will be a white residue on the electrode. You measure the fuel mixture by the length of the residue. Only a little bit near the tip is rich, and a long stretch is too lean.
Hope this helps.

[hotrodhonda400]

yeah if your running light tannish brown then i'd call it a job well done and leave it alone:D just curious but what pipe did ya use and did ya notice a big gain? :confused:

[Holty]

If you're running too rich, are you losing power? my bike runs fine, but it dosn't seem to have the power it did with my airbox lid off. my plug is always black and sooty though.

Guys, I read this string about reading plugs and had quite a good laugh. The only read you will ever get with today's detergent fuels is a MAJOR lean condition, which would be apparent from the popping exhaust on deceleration anyway. I would recommend spending some time on a dyno or just using the old "seat of the pants" gauge to fine tune your jetting. Reading plugs is not a reliable science since the gasoline manufacturers started adding detergents that eliminate the carbon deposits that give the indicators we used to look for. The other indication to look for is a significant increase in fuel consumption, which I had a problem with on my 400 after installing a Dynojet kit. Good luck!

I've never read a plug. I've also read that plug reading went away years ago. My plug is black, always has been,,I don't think it's ever been brown or white,,but I've never put in a new plug took it for a 10 minute ride and pulled it out and looked at it. I was told to just take the thing for a ride after making jetting changes,,which I've always done. If it's bogging or backfiring make the proper changes,,my bike runs like a scalded dog and the plug's not brown so I'm guessin it's OK. It don't feel broke so I aint fixen it..:D