Stuttering

[BeefySTi]

So i am stuttering at 50-100% throttle. Am i correct in assuming that I am running lean? If so, how many sizes should I go up with my main jet? I am not sure what I have in the carb as it sits, so I cant tell you what size jets I have. I only had it out when I first got it to clean the carb, and I wouldn't have known what I was looking at at that point anyway since I was completely new to this. I will pull the carb and jets before I order to I know what I have in there. If not lean, what else could I be looking at? I gotta get this fixed because I am leaving in a month for a weekend trip to hatfield mccoy. Thanks guys.

[Drfat400ex]

Could be lean or rich I belive, myn used to do that a bit before I got the right size and it was rich. Check your plug.

[BeefySTi]

I will do that. about time for a new plug anyway. may cut the old plug and check it out. I am assuming lean because of my airbox vents. there were 4 one inch holes drilled into my airbox lid that the previous owner had done. they had covered them with Duct tape at some point. I recently pulled the tape off and put the uni vents in the holes because I was tired of looking at their sh*tty tape job. That is the only thing I changed. Ran very strong before i took the tape off.

I guess I could always cover the vents again and see how it runs.

[JOHNDOE83]

stuttering usually means rich, if it poppd or backfired at all id say it was lean, if it started stuttering after taping the wholes then it would be rich.

without being there i cant say for sure, i would say that if it started after simply taping the holes it may have been slightly to rich to begin with.

What jets are in there now?

[BeefySTi]

It started stuttering after I took the tape OFF... And wasn't stuttering when the holes were covered. I have increased inflow to the engine, that is why I am unsure how it could be rich. I am gonna pull the carb today maybe and see what jets are in there. Thanks for the replies

[BeefySTi]

took the carb off and pulled the jets. 42 pilot and 155 main is what was in there. the jets had the K symbols on them, so I assume they are genuine and not knock offs. it seemed the A/F screw was turned WAY out. so i turned it all the way in and then turned it out 2.5 turns.

I also pulled the plug and it is pretty carbon fouled. here is a pic:

http://i28.photobucket.com/albums/c226/rcs147/plug.jpg

What do you guys think? Like i said before, it ran fine last year, and the first time i rode it this year. I took it to big rock, went through some water that wasnt more than a foot deep and it started stuttering, but then went away. Rode it yesterday and it it was stuttering pretty bad. other than uncovering the holes in the airbox lid, I havent performed any mods to the atv.

you think maybe the plug was just really fouled and causing issues? I can put it back together and test it out, but if anyone has a different idea, I would like to deal with it before I put everything back together.

Thanks again!

[Drfat400ex]

Hmm I think you're just running rich, but I could be wrong, buy a new plug and a 152 is what I would do and see what happens.

[BeefySTi]

i replaced the plug, sprayed out the carb and put it all back together (I couldn't resist...). I started her up and let her warm up a bit and took it for a WOT 2nd gear pull down my street and back. Pulled hard with no hiccups. I will try to get it out to some local trails we use and really give it a work out this week to see if it was just a junky carb and fouled plug. I know it is probably running rich, but I am ok with that. I would rather be a little rich than a little lean. I will deal with the jetting issue after I get back from my trip at the end of the month. I would hate to re jet it and it end up being lean for the 2.5 full days of riding i will be doing. Thanks for the input guys.