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.

[nditiz1]

I'm interested if they are still available.

When the bucking happens does the AFR shoot to 20s? That would be leaning out. How does it feel if you pull the main stacks and just drive around on the idle jets?

[bbrock]

I'm interested if they are still available.

When the bucking happens does the AFR shoot to 20s? That would be leaning out. How does it feel if you pull the main stacks and just drive around on the idle jets?

Will have to wait for better weather before any more road testing. Pouring rain for the last 3 days and our gravel road is like driving through wet cement. However, I have six miles of data driving fairly level at low speed (20 mph) while the bucking was happening. AFR ranges from 10.8 to 12.3 with 90% of readings in the 11s.

Did not know you could drive without the main stacks in place. Will have to try that when the road dries out a bit (IMG:style_emoticons/default/biggrin.gif)

This morning I started from scratch readjusting the idle air mixture. Tuning by ear settles on the same 2 turns off seat as before. I readjusted the idle speed just a tad higher as I had it right on the margin before. Rebalanced the carbs. I'm now getting a steady idle AFR of 11.1 and the airflow reads just under 4 on the snail.
When I rev the car parked in neutral, AFR dips to low 10s as the accelerator is pressed and peaks at 15 when I let off before settling back to idle at 11.1. Again, I'd expect the AFR to peak somewhere closer to 17 when I come off idle.

BTW, someone will ask - the floats are adjusted properly.