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Posted by: Tbrown4x4 Sep 11 2019, 07:07 PM

OK guys. I thought I had grasp on the air corrector jet function, but my wideband is confusing me. Everything seems to be within acceptable values (12.5 - 13.8 or so) in most drive cycles except WOT.

Example: Cruising 60 mph at 3200 RPM and floor it, AFR drops to 10.3 to 11.1 and stays there as long as my foot stays buried. Or, pulling a long hill in 5th with the pedal floored. Same numbers. Actually pulls cleanly with no audible pinging.

I always thought the air corrector jet was for high rpm mixture control, like cruising at 7000 rpm. The bubbles slow the fuel flow so you don't get progressively rich running at high air flows.

In my mind, from 3000 rpm with a WOT, the air flow isn't high enough to bring the air corrector into play until the engine revs catch up with your right foot.

Am I looking at this the wrong way? And would a larger air corrector lean out the WOT mixture?

BTW, I have 40 IDAs, 200 AC, 130 mains, 28mm vents, 50 (or 55) idles.

Posted by: Tbrown4x4 Sep 12 2019, 04:43 AM

Pointy bolts gets 16 replies, and I get crickets?

Posted by: gereed75 Sep 12 2019, 06:10 AM

At least you didn’t get any turd references.

Posted by: falcor75 Sep 12 2019, 06:27 AM

You have carbs, you cant expect them to give you the same amount of control as an EFI system. Yes 11:1 is a tad on the rich side but then again, you're only loosing about 10% of gas at that specific driving scenario and the excess cools your cylinder heads so it does no damage. Enjoy that you have a car that is working well.

More people probably know why the bolts have pointy ends than knows about your specific problem.

Posted by: Tbrown4x4 Sep 12 2019, 07:14 AM

Yes. Thankfully no turd references.

I supposed I should be happy I have them working as well as I do. But the Swiss in me always expects too much. haha

As long as I have no pinging or black smoke, I'll probably leave it alone.

Posted by: IronHillRestorations Sep 12 2019, 07:20 AM

You might try one size smaller main jet, and possibly reaming it out a little if it's too small. Sometimes that's the only way to dial it in, just try and mark the jets in some way so you know they are different.

Which emulsion tubes? If everything else seems to be within range, different tubes could help. F3, F7 or F11 would be ones I'd try. My Weber books are all packed up right now, so I can't tell you which tubes do what. I'd probably try this first.

Posted by: Front yard mechanic Sep 12 2019, 07:25 AM

Idk what is a wide band

Posted by: IronHillRestorations Sep 12 2019, 07:56 AM

It’s an O2 sensor with a gauge that gives you the air/fuel mixture from the exhaust gasses

Posted by: ChrisFoley Sep 12 2019, 08:50 AM

Yes, and yes. The air correction jet works in conjunction with the main jet, across the whole rpm range where the mains are operating. Ie, approximately from 3000 rpm up to red line.
IDA or IDF? Big difference.

Posted by: Tbrown4x4 Sep 12 2019, 08:55 AM

I have F11s in it. Seems like they're a good starting point for everything.

I should have a step or two smaller mains. I was spending so much money on brass, I figured a PLX would save me money in the long run. It's very sensitive. You can see the initial pump squirt, then the lean spot after and then it swings back into the normal range.

I only have the HP Weber book by Pat Braden. No real talk of what circuit effects WOT operation, just how fuel and air behave at different velocities.

To me, high speed operation and hard acceleration are two different animals. Like I said. I might just be looking at the problem wrong.

I will try the smaller mains and see what it does.

Like Falcor said, a carburetor is a compromise. I just want to it to be a good compromise. Also, I'm a cheap bastard that wants better MPG. I'm filling the tank every three days!

Posted by: Tbrown4x4 Sep 12 2019, 09:03 AM

Oh sorry. I did mean IDF. It's a 1.7 and it probably still has the FI cam in it. Putting up with it until I finish the 2056. I should probably mention it has over 260,000 miles on it, with a quick re-seal and re-ring about 2 years ago.

Posted by: ChrisFoley Sep 12 2019, 09:34 AM

In order to eliminate the lean transition it makes more sense to increase the ac jet size rather than decrease the mains.
One of the AC jet functions is to adjust what rpm the mains come on. After that you can set the Main jet size for best A/F mixture.

Posted by: rhodyguy Sep 12 2019, 09:36 AM

You might find the CB Weber book trouble shooting guide more informative. Any snapping back thru the carbs?

Posted by: Tbrown4x4 Sep 12 2019, 09:36 AM

Thanks everybody! I've got something to work toward now.

Posted by: Tbrown4x4 Sep 12 2019, 09:43 AM

Every once in a while. One of the books called it sneezing?, I think. Not near as bad as it used to be. McMark gave me some good advice about syncing the carbs and setting the idle mixture. It should be a classic thread. I'm waiting until I start a build thread to cut and paste it.