General Category > Quadrajet Carb Talk and Tips
Secondary tuning
Too Fast:
OK so I will put both CV secondary rods back in. You are absolutely the guru, so I take your advice seriously. I don't have any stock 4 bbl intakes. I may put the Performer back on. I haves read reviews about intake manifold testing over the past few decades and you are right about the OE intake, especially at my expected power level and RPM range.
Something I found yesterday was at the distributor the B+ was about 2v lower than at the battery, so that might be part of it.
It must be something I've done, since this issue started when I put the heads on. I KNOW the new heads /exhaust/rockers is really letting the engine breath so much better, that's why I was thinking the carb was lean at WOT.
I should be getting the wide band O2 sensors this week, hope to install shortly.
If anyone else has some ideas, please chime in.
I will report when I get it figured out. Thanks!
Too Fast:
--- Quote from: Kenth on May 26, 2021, 08:48:43 AM ---Standing beside the engine watching the air valve opens when revving the engine tells me the preload on airvalve spring is too loose letting too much air in too soon.
--- End quote ---
Ok, I will adjust it a bit tighter. It doesn't fully open, but starts opening enough I can see fuel flowing.
Cliff Ruggles:
The carb doesn't go lean at WOT because you changed to better flowing heads, bigger cam, or anything else.
Matter of fact increasing compression, better flowing heads and better combustion chambers will like LESS fuel or lean A/F as BSFC is less with the more efficient set-up.
You have a transition issue from reading the first post. If it were lean for A/F it never would pull very well anyplace.
Transition issues more times than not are something else you've changed in the induction system, probably not the better flowing heads.
I remember decades ago removing my iron intake and swapping to an Edelbrock RPM. It required a shorter air cleaner which moved the air cleaner lid 1" closer to the carburetor. Other than the intake that was the only other change.
The engine developed a HUGE hesitation/stumble/bog going quickly to full throttle. Once past it pulled OK. I tried EVERYTHING to tune it out, nothing helped. I removed the lid and ALL the issues went away. I ended up making a custom air filter in the Shaker opening and eliminated the factory style filter and lid.
One wouldn't think that simply moving the air cleaner lid 1" closer to the carb would really make any difference as it still had a couple of inches of clearance, but my set-up HATED it.
Over the years I've experienced the exact same stumble/hesitation/bog with certain parts. I found it IMPOSSIBLE to run an open spacer on any dual plane intake. Divided, 4 hole and semi-open were fine, but fully open produced a stumble that wouldn't tune out. I also tried a dual plane intake once with the divider cut down a 1" clear across it. Same thing, HUGE hesitation/stumble/bog that wouldn't tune out. Put my intake back on and everything was fine......Cliff
Too Fast:
Thank you Cliff. I now have several things to check, I will do a single change at a time and test the result.
I am also ordering a new fuse and relay box to power several things that need isolated 12v sources (feed to distributor, RPM limiter, cutouts, wide band O2 system that arrived yesterday) and will rewire all those circuits. Who knows how stable the 53 year old wiring is like.
It must be something I've done during the big changes I made, because there was no secondary stumble before.
Too Fast:
So the issue seems to be too fast opening of the secondary flaps. I checked the vacuum break/pulloff, it will hold vacuum with the line off when it is pulled shut with vacuum. I release the vacuum tube, it fully releases in a bit under 2 seconds. I think it is too fast for my combo. I nearly plugged this vacuum line, and it is much, much better, taking about 4 -5 seconds to fully release. Now I will loosen the flap spring. It is wound about 1 turn.
The wide band O2 sensors were showing about 15.1 with the CV secondary rods when I am full throttle, accelerating in 3rd from about 3500 rpm on up. I put CE rods in, now it is 13.5-14.0-1 in the same situation. My first car with wide bands, they are gonna be a great for tuning. Trying to get near 12.5 AF ratio for full throttle, then tune the other areas.
Runs great low-part throttle, if a bit lean. Instant 10.2-1 from the accelerator pump squirt, then moderate acceleration is about 13-15-1. Steady cruise is about 13-1, so I have some tuning to do! I will play with the APT now that I can see the effect in real time with the wide bands. Sure was easy to adjust the carb perfectly looking at the AF ratio for idle! The 041 cam will show a little lean at idle, then above ~1000 RPM steady it will be about 14.5ish. Just about mirrors the old way of doing it with a vacuum gauge but now I know both sides are the same. I can get full adjustment on the mixture screws, she idles pretty nicely in gear at about 750-800. About 850 in neutral.
BTW, the air filter lid on this new CAI setup is the same height from the top of the carburetor, and I am using the old RA fiberglass base that I have had on this car for 10 years. The base that came with the Spectre CAI left about a 3/8" gap all around the bottom of the base, they told me this is designed into it but I wanted a total seal so no underhood hot air gets in.
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