Just bought my first bike!!! Running lean tho :(

[theo_mm_]

Hey everyone, my name is Theo. I just bought my 1980 Yamaha xs400 TODAY!!! I’m super pumped and it’s my first bike.

At the moment it seems to be running a bit lean, I am trying to adjust the AFR on the carb. I cannot seem to find the screw to adjust the amount of fuel going into the engine. It seems like I may be missing an adjuster.

Could anyone give me some tips? Do I need to find a replacement?

Thanks in advance.

 

[CaptChrome]

Welcome to the forum!
AFR at idle is adjusted by the screw in this recess of each carb (see below). Screwing it out adds fuel. Other than that, you need to change jets and needles to change fueling.

What is telling you that your bike is running lean?

 

[theo_mm_]

I will try it out and let you know!

A friend of mine who’s been helping me with the process said that it takes a long-ish time to rev back down once it revs up. This, according to him, is a sign it could be running lean.

Do you think that isn’t the case?

Also here is a pic of the bike as of rn if you’re curious! Previous owner really loved it and made a bunch of custom mods to it, like a hand made seat and windshield.