General Category > Quadrajet Carb Talk and Tips
Relocating the UIAB, are size adjustments required?
77cruiser:
Hope it works out.
Cadman-iac:
Well, im in Tucson now, it was a mostly downhill run, from 4600 to 2600+/-.
When i started out I was really panicking as the AFR's were going off the charts, 18.0 plus right from the opening of the throttle and on up to 3300 rpm. If I goosed it then the afr would drop down to 15.0 up to 16.5 depending on the load, but a light load and it's off the charts. I went about 50 miles while watching the AFR gage and the 2 temp gages to be sure it wasn't getting too hot. At this point I stopped and raised the APT a full turn to see if it would make any difference, which it slightly improved, now it's running at 17.0 at 10" vacuum at 3300 rpm.
I went another 50 miles before I raised the APT another half turn, but that didn't make any difference.
Before I head home im I'm going to change the idle tubes to a .035 and see where that puts it. If this doesn't improve anything then I'll increase the UIAB's to a .046".
I have my drill and bits and the new set screws to make bigger LIAB orifices if necessary, so I can go up beyond the .061 that's in there now. I definitely didn't expect the results I got with this last setup. I think I may have just gone too far in the other direction with this setup.
As for an air leak in the idle circuit, I don't see anything that would be a source, everything looks good, gaskets and parts.
novadude:
10" of vacuum at 3300 rpm... seems like at that point, the carb would be almost entirely on the main circuit. I'd try cranking up the APT another full turn. I'm thinking it needs smaller rods or larger jets.
Bigger IABs will just lean it out even more at light load when on the idle and transition circuits. I would not go bigger on these.
AFR meter aside, how does it drive? I would think at 17.0 you'd have some lean surge. If it feels good, maybe the AFR meter is the problem? Collector leak or somthing upstream of the sensor?
My current set-up goes down the road at 70 mph (~3300 rpm) at 15.3-15.5 AFR. If I increase the load by dipping into the throttle to pass, it can swing up to high-16s before the power system kicks in and it goes rich. IMO, this is totally normal / desirable. It seems like 17:1 AFR at steady cruise would likely go leaner as you dip into the throttle to pull hills, etc. Leaner than 17:1, I would think the engine would definitely object.
Cadman-iac:
Yeah, I thought about it before I left Tucson, I raised the APT another half turn, but little effect.
Halfway home I changed the jets to a #73, this was a step in the right direction. The AFR dropped to 14.5 to 16.0 if I remember correctly. I need to use a voice recorder to make notes as it's happening. There's too much information to try to remember it all, at least for my feeble mind anyway, lol!
Thanks for your expertise and input. You have confirmed what I had been thinking, I appreciate it.
Now I just need to fine tune it now that I know what to fine tune. At least I've been keeping good records on what I've done to it as far as the modifications. The recorder will help with getting the results correct.
77cruiser:
How does it run? Does it surge or buck at all. Do you have any exhaust leaks?
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version