Bike sputters at full throttle

[bigbadktm]

First off it is a 85 250r, with FMF pipe and silencer, k&n filter and no airbox lid. it runs freaking awesome on the low end but as soon as it hits full throttle is feels like its running really rich. it is jetted correctly nice chocolaty brown plug, no smoke when it runs all out, just sputters.

Question is...could it be the reeds, or should I try leaning out the main jet more. I am running 40:1 with a 165 main, was at a 162 but I wanted it a lil richer on the top end. Didn't make the sputtering any worse and it runs great at 1/2 to 3/4 throttle.

help

[scottp597]

Stick with what was working before. If there were no sputtering issues with a 162 main then I would go back to that.

[harryredtrike]

an air leak on the intake will do this,personaly i wouldnt go 40-1 but thats me.did you try moving the carb needle one slot?what is the air mix setting at?stock is two turns out.

[haggard 2hundie]

chocolaty brown sounds too dark to me ? i was thinking the ideal plug color was more of a lighter tan color chocolaty brown sounds rich to me just a thought ?

[Yordo02206]

it might be too rich but an air leak will do it to..my tri z was great in the bottom end and at top end it would bog a break up..i found an air leak from the carb to the airbox and fixed it..was ok after that

[Dammit!]

Did it just suddenly start doing this before you changed that main jet? When they start doing that out of the blue when you've made no changes on the bike or in your riding conditions/elevation, it could be the stator went bad. Happened to mine recently and a friend's machine at damn near the same time.

You can pop the airbox lid off (assuming you run one) and see if it improves at all. If it does you're just running too rich.

[Yamaha_Rules69]

It could also be the ignition coil (going to spark plug) I have had that problem before, just as you are describing.

[sstaton1983]

mine sputtered out from about 75% throttle up, i moved my needle one slot and it helped a lot.

[haggard 2hundie]

does it backfire ? that could indicate an air leak as well

[bigbadktm]

well i bought the bike not running so I haven't had much time with it. The previous owner said that it was sputtering before it died on him. I replaced the stator with a used one from this site, replaced the coil and the CDI. I upped the main jet to richen it but it was the same as before, no change in the sputtering. I will try the needle and check for the air leak. Might try going to a 160 or 158 main and see what happens there.

Which way should I move the needle up towards the fat end, or down towards the pointy part? Never messed with the needle before and don't know what the air screw is set at. Pretty much ordered the carb used off of ebay and ran it as is, aside from having to adjust for idle that is.

no backfiring, runs cherry at idle through 3/4 and revs up fine sitting in place and revving it, i think I may try a smaller main first and go from there. might also replace some gaskets on the top end, esp. from the carb to the head and check that intake book for cracks

[haggard 2hundie]

lower the needle to lean the mix , raise the needle to richen, this is where its a little confusing , lower the needle by raising the clip, and raise the needle by lowering the clip

[bigbadktm]

sweet I'll give that a try this weekend along with a smaller main and see if that helps

[portland250r]

how old is the spark plug? the spark plug on my 250r was brown and had never givin me problems and after a while it just wore out.
try that