FZR400 3tj jetting

[petrolhead]

Right its time to do the jetting on the bike ..
I have fitted a YZF 750 system to her And am going to need to put in bigger jets .
From what I gather 120 main jets are a good move ,
Any advice on what size jets would be great , or how big would I need to go to compensate for the system..

Cheers.

[Maelstrom]

This is what I have done with my four stroke racing bikes, and they did win races. It may have nothing to do with what works for you, and if your engine is old and tired then I suggest you do not do it. However, disclaimer aside and all that. Take it to a racetrack that has a generous straight. Set your gearing to pull peak revs in top gear before you reach the end of the straight. Keep going down in jet size until the peak rpm drops. At this point the exhaust should make a sort of burbling noise, like a low intermittent backfire. You may need a friend to listen for it, as you don't always hear it when you are riding. You are now at the point of too lean. Now go back up one jet size or maybe two depending on the jet size increment, altitude, and temperature. Your done. The exhaust note should now have a crisp howl.

The requirement for "bigger jets", in my experience, is a common misconception. Try to remember that tuning is the search for the optimum, and that bigger anything is not necessarily better. One more thing. When you are finished put your old "small" headers back on and repeat the process. Now you can make an informed decision about whether your "bigger headers" were a step in the right direction.
cheers

[petrolhead]

cheers for that bit of info...

[KIYOSHI]

There is no rough guide for carb setup. From experience of jetting/setting up many FZR400s on the Dyno i can assure you the only way to achive your goal without blowing up your engine is a couple of hours on a rolling road.

Take this for example, i set up a new race bike just before xmas which ended up having 92.5 main jets and an air jet blocked off,,,,,,79bhp

I set up another 3tj race bike on Saturday with a relativley stock motor which required 133 main jets to get the fueling right.

Every engine is different,,,,,,,,where abouts are you based? The cost for me to setup your bike on my Dyno is not expensive.

Ta Alex KDC-Racing

[petrolhead]

I'm over in Ireland Kiyishi..
Yea going to have to get her on a Dyno and get her set up..
I took the carbs off and cleaned them but idol is all over the shop ,so just going to get her set up on the rolling road.
She holds a idol alright when I block of an air jet but without it blocked she will sit at 16-1800 and then just fall off and cut out ..
Probaly better to have it done right than me messing and killing the motor..

[KIYOSHI]

Well the man to speak to is engine builder and FZR know it all Leo Aldersley. He has just mooved his business and dyno to Ni

[petrolhead]

Well the man to speak to is engine builder and FZR know it all Leo Aldersley. He has just mooved his business and dyno to Ni

Yea heard Leo has moved here alright but go no info on where he is setting up...
Noticed the website is under construction at the minute ..
Will defo be with him as want him to rebuild the spare motor I have ...
Its good he is here as saves me about 200 on shipping costs..