One other question. Noticed from previous posts the timing was set at BTDC 10 degrees and manifold advance. I have mine set at 5 degrees as specified by the sticker on the hood. I am assuming this of for stock. Should it be at 10 degrees and why different from 5 degrees? I've had the emissions system gutted. I assumed this was done when the weber 32/36 was installed.
second question, Where are you guys porting the manifold on the 258? Any pictures?
Well.... Lots of folks here are sure that manifold vacuum is best for running. It advances the timing at idle for a smooth idle so when you tromp on the gas the timing dives and the takeoff is real nice and smoothly slow.
All the Jeeps I helped remove the computer from all had to pass emissions and I put them all to ported vacuum with the base advance at 9°. That way when you tromp on the gas, the timing jumps up and it will peel tires taking off. When tuning I put a beverage glass on the air filter looking for no ripples, so it is nice and smooth too.
Same deal for emissions, I tried manifold vacuum for a while and when I took it in for emissions it failed miserably. While the tech was writing up the fail, I quickly set it back to ported and reset the carb speed, then had him test it again. He laughed saying I needed more than that to pass. Nope. Bingo! Passed with flying colours.
All of us that I helped nutter (computer bypass) also report over 20 mpg with the folks running stock tires getting 25+. I currently have two 4.0 HO engines running the stock BBD carb and stock 258 distributors on ported vacuum giving 25 mpg and passing emissions.
Even wiki says that manifold vacuum is best for a cold engine, but once it warms up, ported is better. When I got mine in 98, it was set up that way using the CTO valve. It would switch from manifold to ported when warm.
I would highly recommend you try both ways to see the difference for yourself.