Hi all,

recently purchased an FZR400 3TJ track bike. The bike is was equiped and in excellent condition. It has been set up on the dyno running total loss, Air box with no filter etc. The bike was set my friends so i know its genuine. However the bike was never tested on track and when i visited Donnington a while ago the bike ran crap. The bike starts up without choke when cold, ticks over fine but when in mid to high revs it burbles like crazy. When out on the track it seem to ride ok in low revs. and i mean LOW REVS. I was getting left behind on the sighting laps in the slow group. Once i open it up it burbles, and holds back. It was running apauling. At first i thought it was running to lean, but as the end of the can was black we decided to take the airbox lid off. It ran the same in mid range but did pull through and smoothed out. If i kept it in the high revs, screaming it the bike was ridable. Still rubbish and not worth doing another track day until sorted. In the fast parts of the track it ran ok, get into the the tighter sections it really struggled out the corners. Just about every man and his dog past me comming onto the start finish!

If anyone can help it would be great, unfortunatly i dont have much time to spend on it.. or money at mo. Im going to get it on a dyno but would like someone to point me in the right direction. I have already cleaned the carbs, but i think who ever set it up b4 may have put main jets that are too big in it. If i am correct i think they are 112? then again could have been 120 haha. What should they be in a track bike? Thanks, Luke

My bike is a similar set up but with a tuned engine it runs 116 -120 mains with open carbs.
Check the carb diaphams are ok as if the sliders are not lifting it will choke.

Thanks for the reply, my bike has had a mild engine tune... ill take the carbs out again i think, clean them again, and check. Also if still bad, go down a jet size or 2. Thanks again. Luke

If it starts without choke it's too rich down low. Try lowering the needles a notch before you change the main jets. The needles and needle jets control the mid range fuelling, not the mains

I know there's an element of crossover in the jets, but the needles would be the thing to get the most effect from I think, plus it's free to alter the heights

Hello and thanks for your help. After all that i put it on the dyno and its running way 2 lean!!! put 130 jets in it and is better but still not good. We think the carbs are taking too much air??? Luke

hondapower wrote:Hello and thanks for your help. After all that i put it on the dyno and its running way 2 lean!!! put 130 jets in it and is better but still not good. We think the carbs are taking too much air??? Luke

Lol! Shows what I (don't!) know

I'm glad it's better, and you seem to be heading the right way- maybe try raising the needles to richen it a bit?

well everyone i spoke to thought it was 2 rich. All the signs point that way! thanks for all your help. Ill let you know where i get to. Luke

it did remind me a bit of one i rode where the airbox came loose and did the same thing, but to be honest, didnt think it would be lack of air!
i'd take it back to the place that dyno'd it in the first place and tell em they were crap!
i'd be a bit wanting to check what was making the end of the can black!