I finally got a wide band oxygen sensor setup for my car and right off the bat i found the car wanted the secondary jetting as it came out of the box despite the stock o2 sensor telling me it was lean.. so much for that peice of crap.

Anyhow I went back to .095s in the secondaries and the o2 readings look alot better.. but, im still having a problem.. at high rpm, like 5500 on up itstarts to go full rich, like down to 12:1, im thinking im going to need to open the airbleeds up some. I measured the hole on some spare secondary boosters ihave as .025 or so.

So my question is, will opening the airbleeds fix this problemwithout affecting the rpm area underneath the problem, and if so, how muchshould I open the airbleeds up by?

I understand not many people here mess with carters/edelbrocks so you can post the same info as would apply to a holley and I can use that to draw my own conclusions. Any information will be helpfull.

 

Pablo. I'm assuming this carb is vacuum secondary-type like most Edlebrock/Carter carbs.

I would wonder if your fattening on the top end wouldn't be the result of overly-rich secondary jetting. Here's my thinking....

When you first nail it you are opening ONLY the primary side of the carb. Your WOT A/F ratio at that point is determined ENTIRELY by the primary side jetting.

Now, as the RPMs come up the secondaries start to open, a little at first, and then more and more the higher you go. The secondar side of the carb starts to supply a greater and greater percentage of the total A/F mix. So........ if the secondaries are jetted fat your A/F mix will get richer and richer as the RPMs come up, and the overly-rick secondaries are supplying a greater and greater percentage of the total A/F mix.

Make sense?

Not saying this is dead-bang the answer but it's certainly worth the time to try out.

Other things can also affect your WOT A/F ratio like that including a restrictive air cleaner setup (which acts like a choke at high airflows) and a simple thing like just having the lid of the air cleaner too close to the top of the carb- this can do WEIRD things to your A/F ratio that simply can't be tuned out. Fortunately, this is easy to test- jsut take the air cleaner off and make a run. If the problem goes away, your air cleaner assy. is the cause of the problem.

Believe me, I live nd die by methodically tracking down little details like this. Don't drill the bleeds. You are about a zillion things away from needing to do that at this point. Remember, drilling an air bleed is exactly the opposite as jetting. A larger air bleed is almsot exactly the same thing as putting in a leaner jet. It's not going to fix an A/F ratio that ramps up or down. Changing jets/rods is a LOT simpler and can be taken back out if it doesn't help.

 

Thank you damon you always give good advice

The carb is an edelbrock Carter AFB clone, it has the mechanical secondaries with a weighted air valve, 600 cfm.. i removed the choke but one linkage bar remains over the secondaries and I will remove this as this might also be causing the problem.

I did more testing today (new best Et on the Gtech of a 13.7 at 104.09 with a 2.33 60' and new best mph of a 104.44 on a 13.8 with a terrible 60', probably about 103 mph on a normal track, i can work out the math and i have with other runs and it works out to around 1.5 mph since my car isnt pulling real hard at 6000@12:1 when crossing the line)

I think the big improvements came as a result of a few things not the least of which was the jet change to the leaner jets

I also thought about the aircleaner and took it off, still getting rich at high rpm

I see what you are saying about the primary jetting. Heres the thing, the afr is bang on at 5000 rpm and stays realclose till about 5500. I always thought the secondary air valve would have been fully open by this high of an rpm especially on a car running these traps with a 600 cfm carb. Is that not the case does it not open fully till real high rpm?

I had always thought that the high speed airbleeds changed the slope of the fuel delivery.. so what you are saying is that is not neccessarily the case? At any rate, It will be the last thing I do. Im going to get rid of the little choke linkage shaft sitting over the secondaries and see what that does and ill get back to you.


Quote "Believe me, I live nd die by methodically tracking down little details like this. "

You and I are alot alike damon, i love tuning more than I like driving the thing to tell you the truth.. all these minor details, i just love factoring them in and adjusting for them.

 

Pablo, try checking your intake vacuum at WOT while you're watching your A/F go rich. You're right, a 600cfm Edel is a bit on the small side for your engine & RPM range. Sure it will flow the air no problem but not without creating at least a little vacuum in the intake.
If you do read some vacuum at 5500RPM/WOT that may suggest that you're maxing out your carb. A carb will start going rich at this point because of the loss of air density in the intake manifold combined with increased signal at the boosters.

If you want to test the air-valve theory then simply remove it for some test runs. I never run an air valve in mine and yes it does have the effect of leaning out the A/F a bit. I compensate by stepping up the acellerator pump nozzle to cover the lean on transitions, & leave the big end lean. Like you said, the only way to really know is to test everything.

Please share your test results with us.

 

Edelbrocks ain't my bag, but many vac sec carbs right out of the box have the secondary opening spring a bit on the tight side- meaning the air valve may not fully open until very high RPMs. The factory guys don't want to risk a bog by getting them open a little too soon so they err on the side of caution. Definitely true of Holleys and QJets. Don't know if this is true of Edelbrock/Carter but I suspect it is.

I agree- put a vacuum gague somewhere you can see it (duck tape it to the windshield if you ahve to- that's what I do). See what you get. If you're over 1.5-2" vacuum, with the secondaries fully open at high RPMs, you're way outrunning the carb. Not that this should necessarily mean your A/F ratio should start to climb, but weird things can happen sometimes.

Air bleed size won't ramp the A/F ratio one way or the other. Their effect is exactly the opposite of a jet change. They are jsut there to introduce a little bit of air into the fule before it hits the booster. Turns it into something like "capuccino foam". When the "foam" hits air stream the air bubbles in it basically "explode" and help greatly in atomizing the fuel for good fuel distribution. Generally there's not much reason to mess with the high speed air bleeds unless you REALLY know what you are doing and why.

Drilling out the bleeds on the IDLE circuits can sometimes be a very helpful tuning aid since there are no replacable jets for the idle system (just idle mix screws which only affect curb idle, not the off-idle part of the idle circuit).

 

So you remove the air valve totally? whoa, do you think i can get away with that with my carb? it needed quite a bit of pump shot as it sits, im rnning .035 shooter and have it in the hole closest to the pump arm fulcrum

i have noticed that it initially on just slight tip in in normal driving introduces way too much fuel but if i slam on it at wot its just right to maybe a hair lean.. thats another thing thats pissing me off, just a slight touch of throttle and the thing is down to 11:1

youd think that the shooter size was too big but i had it with the stock 028 shooter before and it was terrible, moved up to the 35 and the car is good.. maybe it needs more volume and less shooter... hmm
thats another problem though

im gonna remove the choke shaft tomorrow first thing and go for a test drive see what the wide band has to say about that.. then move down the list methodically changing things

 

Update


I removed that choke shaft. I really should have been taking notes on the weather conditions these past few days, I.e. barometer and temperature because its kinda hard to tell whats making the biggest difference

anyhow, now it seems to be lean but the curve is still the same. I lost 2 mph in the quarter and now instead of 12.7-13.3 afrs up to 5500 its more like mid 13s solid all the way up.. gets pretty lean actually. It still is curving rich though, up by 5700 its down to 13.0

Ive noticed a couple funny things too, contrary to what I would have thought it seems like the longer i drive the car and the hotter the day and car gets the leaner the wot mix gets.. I could be wrong though on this one since i really havent been paying close attention to it.. just sorta seems that way

another thing, the faster I go the richer it gets. Seems like first gear is ultra lean on the WB, and second is slightly richer and so on and so forth. The onlything I can think of is that at low speeds the air is accelerating so quickly through the carb that the fuel cant keep up and as airspeeds slow down (higher vehicle speeds) the fuel starts to catch up. Whaddya think?

anyhow, i might jet it back up to see if i can get back to where i was

 

I did two things that seem to have made a pretty big difference

I upped the jets from 095s to 098s and I put a much lighter spare airvalve I had. The car feels good allthough i havent tested it, the AFRS are MUCH closer now, They pretty much seem to stay flat at like 13.0 or so, could be a little richer in peak torque but im not complaining, it is pretty darn close. Still starts to get a little richer on the top end but we are talking .1 or .2 richer.. much better
I really wish i could taylor the curve to be like 12.7 around peak torque and 13.2 or so round about peak hp but I guess for that kind of precision im going to have to throw on my FI