1977 re-jetting

[nculver]

Hello all you wrencher's out there! I'm new to this scene, so please excuse my ignorance...

I am working on my recently purchased, semi-barn find, 77 xs400. It came to me without an air filter. Now, I've gotten it running, though running rough. And I am assuming 75% of the problem is the lack off air filter affecting the air pressure. I set the idle mix screw to factory specs, as well as the float bowl. I am considering buying these filers from Mikesxs.net:

https://www.mikesxs.net/product/15-0027.html

The 57mm XS Performance Pod Air Filter. I also understand I will need to re-jet my carbs. Does anyone have a resource where I can research correct jet sizes. Or maybe even just know what jet sizes I might need?!

Thanks so much for your help!

 

[xschris]

57 will be to big. These carbs take 54mm. I would use factory air filters and boxes with the factory H-pipe for best operation. If you run pods run them on The H-pipe. You will get a better tune. Real K&N or uni's work good. These bikes often idle best at 3 turns out on the mix screws with factory setups. There are lots of threads on jetting in the forum so use the search function for that. Post some pics of the bike so we can see what you have.