Running really lean, time to rejet my Weber!

[ken_79-fj40]

Last night I pulled off my intake and header to change the gasket I thought migh be leaking due to dieseling problems and a rough idle. Plugs looked a little lean when I did my valve adjustment after running the the new motor in for a few hundred miles. My intake wasn't leaking but I am sure glad I saw this:

I hate to think of what running it this lean would do to it over time. Apparently out of the box Weber 38/38 jetting doesn't agree with my shaved head, high-rise carb adapter, and 262 duration cam too well. Anyone have any suggestions on where to start with jet sizes? I was thinking going up 2 sizes on everything to start, but i've never messed with jetting on a Weber before. I've played with the Holley on my mustang a little, and i've got a bunch of Weber jets at work.

 

[76FJ40]

From my experience at ~500' above sea level 47s were too lean and 55s were too rich. Thyat should give you a place to start. My head has been shaved 0.080" and the PO installed an aftermarket cam.

 

[ken_79-fj40]

Good to know as i'm not too far above sea level myself. So I assume you only changed the idle jets in the sides? Mine are currently 45's but the main jets are 142 and the air correction jets are 185. I didn't take the emulsion tubes out. I may actually start with just changing the idle jets. Besides the dieseling and rough running below 1000 rpm the truck actually runs good with no hesitations and the plugs are a tannish color and not white like they were when I tried to lean out the Holley on my Ford.