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]

Spent time over lunch and after work meticulously dialing in the carbs. I lost count of how many rounds of balance-lean idle mix-idle adjust I did. I am certain I am not idling with progression ports exposed. I checked with both a vacuum gauge and by ear on the advance vacuum port. For the idle mix, hooked up my low range tach instead of doing it by ear. This time the mix screws ended up less than 1 turn out from seated even after adding a half turn richer per John Connolley's method. Smooth and steady idle as before but the AFR still reads in the 10s at idle. I feel pretty confident a jet swap is in order. Can't say if it needs to go up or down but am betting on down.

I also pulled the main stacks and drove very briefly at lunch. I have two pro tips from that little misadventure.

1. If you decide to go driving around with the main jet stacks pulled, keep the stacks with you. They do you know good when you run out of oomph to get back up the hill if they are on the bench in your garage. (IMG:style_emoticons/default/screwy.gif)

2. If you remove a CSP linkage rod to balance your carbs, it is a VERY good idea to put it back on before driving around with the main stacks removed. Running on 2 cylinders with no main jets will DEFINITELY not give enough oomph to make it back up the hill. Same as before, the rod does you no good sitting on the bench in the garage. (IMG:style_emoticons/default/av-943.gif)

3. Bonus tip. If you ignore the first two, make sure you have comfortable footwear. You will need it.

Yes - I am a complete idiot. Luckily I didn't get too far away but did get caught by my neighbor who got a good laugh out of it. (IMG:style_emoticons/default/blink.gif)