Possibly wrong jetting? i dont know...someone please help!!

[Cool Guy07400EX]

Ok so i just recentley installed a Curtis sparks X6 big core exhaust and a k&n filter. I live in Phoenix, Arizona so elevation is close to 0 :] I took it out for my first ride with the new stuff today and it sounded great and i could feel a big diffrence in power but there is one problem... it seems to be backfireing alot after i run it awhile and then when i let off the throttle is when it does it. A guy at a shop told me to run a 155 main jet so thats what i have in it right now. I still need to find the idle screw and screw that out 2 1/2 turns but i doubt that will fix the backfireing. So if anyone could tell me a diffrent jetting setup that might work or if i have the right jetting and its just a diffrent thing thats wrong with it or what. please help!
Oh and also if anyone could tell me where the idle screw is preferably by using pictures..that would be great. Thank you!!:blah:

[CSR400EX]

if you are talking about the air/fuel screw, then it is circled in the pic below

http://i220.photobucket.com/albums/dd193/CSR400EX/pilot3.jpg

[QuadManiac]

Definitely richen the pilot screw... it backfires because idle adjustment is way lean.

[Cool Guy07400EX]

So then the idle screw or what csr400ex said "the air/fuel screw" just needs to be ajusted??:confused:

[97WarriorRider]

the air/fuel screw is the pilot screw..Not the idle screw..they are 2 different things.

[the Z Man]

Did you put new exhaust gaskets in?? could be leaking there, it usually will backfire on decelleration...

[Cool Guy07400EX]

Ok sorry im retarded with jetting :blah: :D So then would the air/fuel screw be the screw that the guy at the shop told me to turn 2 1/2 turns out?

As for the exhaust gaskets..are those the things that connect the header to the engine?

And im pretty sure the backfiring is coming out of the back of the pipe.

[QuadManiac]

Try turning the pilot screw 1/4 to 1/2 turn counter-clockwise to richen it up a bit.

[the Z Man]

Its backfiring out the back from air leaking at the front.

[BigBore24]

if your still running the stock pilot jet, you may need to go up to a 40 or so. if you back the pilot screw out much more than 2 1/2 turns total then i would change the pilot jet.

[CSR400EX]

that reminded me lol, Sparks calls for a 45 pilot as well as a 155 main. that might be your problem.

[Cool Guy07400EX]

Well then i think im just gonna go ahead and change the pilot...but to a 40 or a 45??

[Cool Guy07400EX]

Actually you know what scratch that last thing i said. i think im gonna turn the pilot 2 1/2 turns out and if still backfiring ill just change the pilot to a 40 or a 45.:rolleyes:

[Cool Guy07400EX]

Ok i think i actually just figured out what could be the problem thanks to z man. i did not purchase new exhaust gaskets with my pipe. so i will do that and install them then get back to you guys.

Thanks for the help!!:D

[Cool Guy07400EX]

Ok well i just went and tryed to find the air/fuel screw and turns out there is no screw in there at all! what i doo just buy one from a shop??:confused:

[the Z Man]

its way up in the bottom of the back of the carb, real hard to see, it doesn't protrude either,

[the Z Man]

400ex actually has it in the front, from what Riva shows, if thats it its #6 and can be bought as a set, its like 18 bucks.
riva original online parts finder

[red_rider_069]

Originally posted by Cool Guy07400EX
So then the idle screw or what csr400ex said "the air/fuel screw" just needs to be ajusted??:confused:
yea fuel and air is to adjsut to elevations usually.. idle is to adjust how much gas goes into your carb.. its like holding the throttle down.. oh yea and im moving to pheonix=) .. go riding at the river.. drag races are badd =).. ever been there?

[Cool Guy07400EX]

Originally posted by the Z Man
400ex actually has it in the front, from what Riva shows, if thats it its #6 and can be bought as a set, its like 18 bucks.
riva original online parts finder

Is that to buy gaskets or a new air/fuel screw?


yea fuel and air is to adjsut to elevations usually.. idle is to adjust how much gas goes into your carb.. its like holding the throttle down.. oh yea and im moving to pheonix=) .. go riding at the river.. drag races are badd =).. ever been there?

I dont think i have rode there before.