it sounds like it is getting too muc fuel, you having to switch the spark plugs tells us that they are gas fouling, which is caused by too much fuel.

check to see which groove the needle is on. putting it on a higher groove should help you control the fuel mixture better.

the top of the carbs should be pretty simple.
no diaphrams in them, just the slide a spring and a cable. but check to make sure the carb cap is on snugly.

sometimes they will be set differently if the carb is just a small amount different inside due to casting.

but once you have them tuned together it should really run well.  

A  

WOLF1, seems like your the man around here. Maybe we should do a story on jetting? You interested?

ATVR Editor  

sure thing, want pictures?

just a career technician and cycle repair shop owner.

certainly not "the authority" but after 20 plus years i do still love my job.

i think maybe do one on a blaster and banshee as well.
If you have ever tried to set the carb on your own banshee or blaster then you'll know the frustration it can cause.
let me know how and when i can help.  

Wolf1

Just wanted to give you an update on my electrical issue. Personally I gave up on the bike as I began beating my head against the table and was dumbfounded as to what the problem was. I check, rechecked, and triple checked everything electrical I could think of. A friend of mine works with a guy who builds drags quads (never knew there was such a thing) but I dropped it off at his house and 3 hrs later he called to advise that the issue was in the carb. Apparently behind the throttle cable connection in the carb there is a switch that stuck when I was flipping the carb back and fourth as I was adjusting the fuel mixture screw. Well, I gave the jet kit to him and told him to do whatever it needed. The problem was something that I would have never checked.

Thanks,

Steve  

yeah it's not easy to diagnose every atv over the internet.

there are times i'd love to have the atv for a few minutes just to give it a once over myself.

sometimes the ones that seem the easiest really need to be looked at.

glad you got it figured out.  

yeah wolf1 i have the 2008 yfz 450 and i have just put on a K n air filter,HMF race pipe,9 curv rev box,and a jet kit pilot(45) main(170). in neutral and low gears if you get on the throatl it will stumbl and fall on its face.but once you get going it runs like a champ.what do i do to fix this problum.and i have fidled with the air/fuel mixture screw.please help  

by stumble do you mean it bogs down? or cuts out?

if it bogs down then it is getting too much fuel

if it is cutting out then it's not getting enough fuel.

what groove is your needle set on?

if it is cutting out then try setting the needle on a lower groove.

if it is bogging down then try your needle on a higher groove.

of course you will need to readjust the fuel air mixture.

is this a jet kit supplied by hmf with the exhaust?  

yeah that red screw with the numbers on it is your fuel air mixture screw by the sounds of things you have a msr adjustable fuel screw in it which makes the carb much more easy to adjust (i have one) so what i recomend is cleaning your carb and follow the instructions that wolf 1 gave you.if that doesnt work you might have to consider installing smaller jets.

good luck dude. i hope you get that thing running well.
yfzs are monsters when there well tuned  

yeah wolf1 when i said stumbl i meant it wants to cut out.and on the needle there are no grooves.the jet kit is supplied from hmf when i got the pipe.by the way i not totaly shur which way to turn the air/fuel mixture screw to get lean or rich  

if it is cutting out then it isn't getting enough fuel.

turn the fuel/air mixture screw to the left to add more fuel.

mark where it is setting and keep up with how many turns you make.

but adjust it in 1/4 turns, let it run or a few minutes between 1/4 turns.


yeah the jet kit supplied sometimes only has one groove.  

i just purchased an 04 yfz that is doing the same thing i am looking for answers too. any help you could give on what you have found out would be appreciated.i live in canada and have checked all the things you have. i dont go on the computer much so you could either just reply to this post or call collect 250-552-2959 i would really like to get out and enjoy this quad but am at a stand still. thanks  

which one did you refer to as having the same problem?
sorry this post is 5 pages long, and i wanted to make sure we were on the same page.

if you don't mind post what it is wrong with it.

if it's the last post by hoghunter55 then follow the instructions i gave.

if it is cutting out then the fuel mixture is too lean, if it is bogging down then the fuel mixture is too rich.  

sorry guys im new to the site and thought it would show that i was refering to hatcher0911 s problem. thanks guys  

kurtvlchek:
i just purchased an 04 yfz that is doing the same thing i am looking for answers too. any help you could give on what you have found out would be appreciated.i live in canada and have checked all the things you have. i dont go on the computer much so you could either just reply to this post or call collect 250-552-2959 i would really like to get out and enjoy this quad but am at a stand still. thanks

sorry guys im new to the site and thought it would show that i was refering to hatcher0911 s problem. thanks guys