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.

[NARP74]

They were originally tuned at a much lower altitude, ran like crap at 6k ft. I had them retuned at 6k ft and those are the numbers I posted. Not sure what they were when I got it here. It did run poorly before the retune, spitting and popping at idle and low cruise out of the neighborhood. Ran a little better after a warm up, but still not great.

[bbrock]

They were originally tuned at a much lower altitude, ran like crap at 6k ft. I had them retuned at 6k ft and those are the numbers I posted. Not sure what they were when I got it here. It did run poorly before the retune, spitting and popping at idle and low cruise out of the neighborhood. Ran a little better after a warm up, but still not great.

Thanks for the clarification. Super helpful! (IMG:style_emoticons/default/beer.gif)

I have some better data now. I drove the car down to the valley (5,000 ft. elevation) where I could find long stretches of quiet road relatively level. It's clear the idle circuit is running rich. Consistently rich () through all speeds @~3000 rpm up to 50 mph.

0-50 mph: ~10.5 - 11.5 but mostly right at 11.0
Cruising level 50 mph: 11.5-12.1
Cruising level 60 mph: 12.5
Cruising level 70 mph: 13.5
Cruising level 80 mph: 13.5 - 14.0
WOT: ~12.5

Even at high cruising speeds the AFR dips down to low 11s/high 10s if the throttle is backed off to just barely past idle.

It seems AFR is pretty good whenever it's pulling from the mains, but as soon as the throttles close to idle/progression, it pulls too much fuel.

I just ordered 2.10 correction jets and a set each of .45 and .55 idle jets. That way I should have a combo that will work better than the current setup.