Need Carb Jet Guidance, Weber 40 IDFs Options

[bbrock]

Plans to Megasquirt my car got delayed over the winter so my Webers will stay on for another summer. So, I finally hooked up my wideband to see if any adjustments are needed to keep the engine happy and safe until I can do the conversion.

The only real "problem" area is idle and low speed driving on the progression circuit where it is running too rich. It idles smooth and steady at 700 rpm with AFR of 12.3. That with idle mix screws ~ 2 turns off their seats. That's the leanest I can adjust and keep the engine happy. Just off idle at 20-40 mph @3000 rpm it goes even more rich to around 11.0 +/- 0.5. I don't think that's alarmingly rich but wasteful and I do get a bit of annoying surging/bucking driving below 30 mph.

Current jetting is as follows:

Venturi - 28
Emulsion tubes - F11
Main jet - 115
Correction Jet - 200
Idle jet - 50

I'm thinking I should reduce the idle jet but not sure by how much. I can get .047, .045, or .040. Any suggestions?

I could also use some advice on mains and/or air correction jets. If I didn't plan to swap the carbs to FI, I'd try for a little leaner highway cruising mix for better economy and maybe flexibility. In limited testing running in good ranges for performance at the expense of economy - WOT ~12.5, Highway cruise ~13.5 but rarely goes above 14.0 even on downhill and decel. Weather is crappy here this weekend so I've only done a short drive in hilly conditions. I need to get it down in the valley for some long level runs to see where it settles. I think I can live with the numbers I'm seeing now, but do wonder what it will do when I attempt to cross a 10,000 ft. pass. I'd rather it not die of oxygen starvation if I attempt it. Any thoughts?

BTW, I live at 6,000 ft. elevation so I'm not surprised it is running on the rich side with out of the box jetting.

[bbrock]

Well, I'm not sure if I took a step backward or forward tonight. I drove to town and bought new set of spark plugs. Drove to a nearby park and put them in. Then I readjusted the idle mixture screws but had a helluva time dialing them in. Car was stuttering worse than ever and farting and popping. Mix was lean not matter what I did. Really lean, like 15s. Stopped one more time before leaving town to readjust and back the mixture screws out enough to richen the mix. Drove home with the car sputtering and popping and got home in a REALLY bad mood. Thought I'd go back to basics and check the timing again. Went to plug the vacuum ports and found the retard port open. Yep, I must have snagged it and pulled it off changing the plugs! (IMG:style_emoticons/default/headbang.gif) At least it was a simple fix. Oh, and the timing was spot on.

With that out of the way, I was able to put a really good tune on the carbs with fresh plugs. Running smooth and sounding good again, I plugged in the computer to read the AFR. Idled at 10, driving 20-30 mph up to 3000 RPM, steady low 10s. AFR is also much more stable than before. No more jumping around. So at least my world makes sense again. .50 idle jets are too rich, .55s are really too rich, and .45s are too lean. Seems obvious where I need to go next. My hypothesis is that the fouled plugs were causing enough stumble to spoof the wideband into reading more lean that it actually was. That's the best I can figure anyway.