chugging a bit too much

I just bought a 99 wr 400 (what a bike!). The bloke who had it before me has done a bit of work on it, and good work too. the only drama i have is (i think) the oversize jet in my carby, through the bush is unbelieveable, goes like a shower of you know what! However on the road at about mid revs runs as rough as guts. Am i on the right track thinking this may be the jet? any reccomendations on the size i should be putting in?:lol:

try moving the clip on your needle up one slot first. Sometimes just lowering the needle will work. If it get's better but is not great then you know your on the right track and need a smaller main. Drop a size(i.e. 160 to a 158) and go for a test ride. Don't forget to put the clip back to the slot it was in, you only want to change one thing at a time.

sounds like a typical lean needle. I agree with Lcpl0331....move the clip on the needle down one notch and see if it betters.

FYI my settings with a full exhaust:

170 main, JD blue needle 3rd clip down

sounds more like the infamous tps stutter to me

tps stutter?

I was thinking TPS too and I know the WR400 had a TPS on it...

Unplug it and see what happens:ride:

Not to appear too much like a dumbass...... What does tps stand for and where is it located??

(by the way, thanks for the help)

Not to appear too much like a dumbass...... What does tps stand for and where is it located??

(by the way, thanks for the help)

Throttle Position Sensor. It's the piece connected to the only electrical wire coming off the carb. Unplug it to see if your surging stops. DO NOT unbolt the sensor from the carb as re-adjusting it can be a pain in the ass if you decide unplugging didn't alleviate your problem.

Thanks heaps, i'll give it a go tomorrow. If this does solve my problem, what should i do as a permanant fix? is this going to do any damage if i leave it off? (assuming this works)

Thanks again, i really appreciate it!

You boys are champions, that made so much differance!!! It's running like a dream! If this is such a common problem, why didn't yamaha fix it? And what if i now leave the TPS unplugged? could this cause more dramas?

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