Question about my spark plug color??

[jt29]

Here is what I have:

Stock motor, Stock pipe with the S/A and all the guts cut out, Aluminum air box with a heavily modified lid, and K&N air filter.

Here is what I did:(Rejet)

Stock # 38 pilot, needle and clip still stock settings, but changed the main jet to a 150.

Here is the out come:

The spark plug was a dry, flat black color to start with. After re-jetting the bike it is still flat black around the base of the spark plug. But at the tip, the little arm piece that you set the gap with is tan/brown with a tad of white. Is that good or do I need to make some adjustments? 0-1/4 throttle is great the flat spot is gone. 1/4 to 3/4 is good, and 3/4 to WOT is better then before I jetted it. But it does back fire when I let off the throttle and during deceleration. Also staring the bike is no problem. What do you guys think???

[Chino886]

I would say bump it up to a 42 pilot and go a couple more on the main since you are backfiring, you don't want to run lean....

[jt29]

Why would I want to go with a 42 pilot, it starts fine and idels good.



Originally posted by Chino886
I would say bump it up to a 42 pilot and go a couple more on the main since you are backfiring, you don't want to run lean....

[Chino886]

42 works great....if you like the 38, then stay with it....I just recommended it....

[jt29]

what will the 42 give me over the 38, and will that make it run richer or leaner??

[400exrider707]

Originally posted by jt29
what will the 42 give me over the 38, and will that make it run richer or leaner??

try a 40 first, larger pilot will make it richer. With your mods the 150 main should be ok, but if its lean go to a 152. You really should use a new plug to take your readings, once a plug has been used, its hard to get it to change colors again. Get a new plug then go from there. The backfiring from deceleration is lean condition on the mixture screw. I cant remember which way is richen, but thats all it is. I belive you should loosen the screw. Take it out 1/4 turn at a time until the backfiring goes away.;)

[Pappy]

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

[GOTFEAR]

I wood fix the pipe first the gutted pipe fix it and then start jeting it. it will run better and sound good

[jt29]

I did try the #40 pilot and I could not keep the bike runing at idle. It would idle for a little bit then die, and the engine was warmed up. I put the #38 pilot back in and it started fine and idled great.?? I will get a new plug.


Originally posted by 400exrider707
try a 40 first, larger pilot will make it richer. With your mods the 150 main should be ok, but if its lean go to a 152. You really should use a new plug to take your readings, once a plug has been used, its hard to get it to change colors again. Get a new plug then go from there. The backfiring from deceleration is lean condition on the mixture screw. I cant remember which way is richen, but thats all it is. I belive you should loosen the screw. Take it out 1/4 turn at a time until the backfiring goes away.;)

[04TRX400EX]

Like what was said before, your best bet would be to stick with the 38 pilot since it runs well with it and idles well to 1/4 throttle. I would probably say go to a 152 main but definately change the spark plug to a new one so that you can actually see what it is, not what it used to be. Pick one up from your local dealer for like $3.

[jt29]

Cool thanks for the info. helps alot. Should I just leave the needle alone??