Yamaha XS400 special-82 open air filter jetting?:


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Hi I'm new to this forum and bought myself a nice xs400 which is about to be modified to a nice white brat style machine..

Well I want suggestion for jetting with following setup.

Air box with original exhaust but some Otis silencers? Are they perfomance silencers? Same shape and design as original. Amy inputs?

Jetting is:
Main :125
Pilot/slow :42.5
Air: 150
Needle 4th from top position
Air screw : 2.5 turns out

My plan is just slightly ported headers and open air k&n style filters which has an oval design..

Any suggestions were to start?

I think main is way to lean?

From what iv'e read slow and main should be main 145 and slow 45 when using open air?

Appreciate proper help and answers
The stock carbs on your XS400 are CV type carbs. They use a vacuum signal to lift the slides. The pleated element air filters such as the K&N or the knock offs disrupt the air flow through the carbs enough to disrupt the vacuum signal for the slides. The more tapered or oval the filter the stronger the effect. The long round straight one is better but not the best option.
A straight round foam filter performs the best. I like Uni-filters. These give plenty of smooth flowing air.
I spent weeks trying to tune out an off idle flat spot using K&N filters. I heard about the Uni-filters and bought a set and the flat spot is gone.
Hmm okey.. Well but I does seem to work for a lot of people tough..

How about jetting what is original for soch xs400 special?

From what I've read 135 is main on my bike but a lot of people say 142.5 is original..

And now mine is 125...so should I try 135 or 145 main ? With open filters?
I use k&n on three of my xs400s' with great results. You need to keep the stock H-pipe and use real k&n filters. I use them on my 80, 81, and 82. All have the stock oem exhaust but has the richer running 76-77 xs360 carbs. With those carbs, the settings are 1.5 turns out on the pilot screws, third clip on the jet needle and 135 mains. With 400 carbs and an aftermarket exhaust you may need to jet a little. But it will all be a trial and error till you find what works. DSC03112.JPG DSC03113.JPG DSC03114.JPG 4376-1375883337-c15290261011cadeb1b4981dff9734a7.jpg
Ok.. thanks for answeres but i have not gottten any suggestions for jetting yet.

i bought 140 and 145 main today.. the shop didn´t have 142.5 main or 45 pilot jets, but ordered.

my new settings in the carburator is 140 main and airscrew - 3 turns out as the shop said that anti clockwise for more fuel on lower rpm

is that correct?

i´ve found that my aliexpress airfilters outlet os actually to small vs intake on the head and that it partually covers the flow around the air jet..

ill attempt to grind out the airfilter to fit original intake hose straight on the the filter for a more even flow over the carburator.

Well about the h-pipe iontake hose..

i just simply dont have any... ive got at plastic intake without any tubes.. how come it´s different.. i do live in sweden and maybe the xs400 special were different over here?
It's definitely soch..
and yes definetly no h-pipe..

what about my exhaust is that come exhaust from auto a perfomance upgrade of some sort or just plain simple an aftermarket replacement?


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and as u all can see I've changed the spark plug cap for an mad that hat no resistance. vs ngk original which has 5k..

is there any better coils out there from another Yamaha or something else that is bolt on?

what is best?
always thought less resistance better spark but from what I've read the 5k actually sparks better ??
seems weird to me
Looks like one of the euro models that has a bunch of earlier parts from other bike in it. I see it still has points ignition and coils on it. The exhaust look like an aftermarket. If the mufflers are clamped on and there is no crossover pipe between them than they are. I would search the forum for ignition options.