1983 jeep cj, head swap, manifold vacuum

[Beaulac]

I have an 83 cj - AMC 258 i6 / 4.2l with the 4.0 head swap - header, mild comp cam. Having weber carb problems, and was wondering if anyone had a similar setup and could tell me what your manifold vacuum was? Mine is showing 13-14 inches . The engine has been rebuilt about 2500 miles ago - new head. I am wondering if this is too low to run the weber 38 idle curcuit properly. Right now it only idles with the first transition hole exposed. What could cause this vacuum to be so low? I have my vacuum advance hooked to the manifold, not the carb, and have my timing set at 12 degrees (without vacuum advance). Also - No vacuum leaks (at least that is what a full can of WD-40 says!)

 

[CJ]

That is a pretty low number, my cammed V8 would pull 17.

 

[IOPort51]

where did you find the 12 deg.?? I am not at my library but 8 deg BTDC sounds a bit better.
some one tell me I don't have a clue.

 

[Sasquach]

8 degrees is correct for my 78

 

[priceg]

Stop, put down the vacuum gauge,15 inches is close to perfect.

 

[Beaulac]

I got the 12 degrees from the guys at Redline, and from a few of the forum posts. I swapped off the Weber this weekend, and tried a Rochester 2 barrel just to see if it made a difference - Same exact symptoms - Rough idle - big drop in RPM when placed in Drive - and then even rougher running. I am at a loss! - might try compression test?? Checked PCV valve - rechecked plugs and gaps - tried all different degrees of timing (at 8 degrees the idle is so low that the speed screw needs to be out almost 1.5 turns!) -

 

[priceg]

Check this just to eliminate.

 

[Beaulac]

Would it even run if I had the firing order mixed up?? The jeep will idle (not even badly) and runs just while driving. I can stop at lights and it will stay running, but I know it is not running properly on the idle circuit. Also - I have owned this jeep since 1993, and prior to my engine overhall I was running a stock AMC 258 i6 / 4.2l with about 40 compression on one cylinder, and 55 on a second (burnt and seized rings) With a complete rebuilt, a 4.0- L head and cam, MSD ignition, and a header, I expected quite a different driving experience. It does not miss under load, but 65 - 70 mph on the highway is a struggle. Also the idling issue. I expect this jeep to move a lot better than before, and to idle perfectly with the improvements I have made. If this was an old engine, I would be content and just drive it, but the 9 mpg, and stumbing are not right. I am still thinking Cam (valve) timing might be off a tooth.

 

[priceg]

I guess it is time to go back to the basics and start eliminating systems.

 

[Beaulac]

At least I can eliminate the Carb from the equation....Damn... I hate chasing a spark issue!