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Very rich cruise condition - 440 Brawler 850cfm

andrewwoz

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Working on tuning the carb on the 440 in my super bee, I have an Innovate LM2 wideband with the sensor on the pass side collector. I had been having a lean condition (15+ afr) when going from cruise to light/medium acceleration, going from a 6.5 to 10.5 power valve cleared that up. I am now working on leaning out light throttle cruise, currently at about 12.0 AFR when maintaining speed from 2-3k rpm. This condition was identical before the PV change (vac is 15 at cruise so PV is for sure closed)

Primary T slots are square, the secondaries are not showing at all, exposing them would make the idle way to high. Should I close the primaries more (bringing them to less than square) and open secondaries?

Based on what I have read it seems like my next step would be adjusting the IFR's? Currently at 31, thinking about stepping down to 29. Do you typically change all 4 or should I start with just the primaries?


Car/Engine specs (how I bought the car)
69 Super Bee A833 4 Speed/3.55 gear/29" tire
440HP lower end with estimated 10:1 comp
Trickflow 240 heads
Comp Magnum 305H ([email protected], .525 lift, 110LSA)
Performer RPM manifold
Brawler 850 race
Dougs 2" headers/3" exhaust
MSD 6AL/Pro Billet Distributor/Blaster Coil

Timing is at 22 initial with a 14 advance bushing (36 total with 1 heavy silver and 1 blue spring), idle/vac will increase if I advance initial more but how much is too much?
Vac at idle is around 6-7, thinking this is related to the cam?
Vac at cruise is 15-16
Idle AFR is right around 13.0
Main jets are 72 and 84, I think I will end up dropping the 84s down but not worried about WOT just yet.
 
I have a 950 thumper modified carburetor. In order to get it happy, the jets had to be dropped about 4 sizes front and rear. Make sure your idle air bleeds are 73. And the high speed air bleeds 28. At cruise my afr's are 12.7 13.2. But the exhaust is clean and plugs have never looked better.
 
Does this carb have adjustable idle by pass air? Just wondering how you got the t slots correct on pri & no T slot showing on secs. Would expect t/blades would need to be open further at idle with such a big cam.
 
Does this carb have adjustable idle by pass air? Just wondering how you got the t slots correct on pri & no T slot showing on secs. Would expect t/blades would need to be open further at idle with such a big cam.

It does not from what I can tell, and no holes in the blades. I only visually set the primaries t slots with the carb off (it was pretty close already) maybe I will give it another try and measure them.

Would having the primary t slots less than square negatively affect anything?

At some point I am going to put a smaller cam in the car, I don’t have any plans to race it and would prefer a little more low/mid range power. I’m also thinking about a vac secondary carb, maybe a Quick Fuel SS 780CFM or 880CFM
 
I was told to back the idle screw so the throttle blades are completely closed. Then turn them clockwise 3/4 of a turn and you should be set.
 
as I recall and it's been a while because most of the stuff I did with holleys has been marine! I've heard the only way to thin the mixture for mid throttle on a holley was to pull some bare copper wire bent over on each end through the metering block passages to reduce the size! [not sure if this works or not but it didn't come out of my head}
 
Maybe I missed something. Why not reduce primary main jets to 70?
 
You need to watch closely as to when it is rich. On my carbs, the transition from the idle circuit to main jets is 2300-2500 rpm. If you are rich below that, then put in smaller ifr's. Mine always end up at 29 or 30's, and I change all 4 together. If you are rich above the transition, then go with smaller main jets.
 
Do you have a stock PCV valve? It would be open with that huge cam & admitting a lot of air, could be why t/blades are able to be closed down.
 
What the air fuel at off idle cruise? Did you try jetting the primary’s down to see if it helps? A lot depends on where the main circuit takes over. If you need to lean the cruise prior to the boosters being on the IFR,IAB play into that. But, if the idle is good and you have good adjustment on the idle screws sometimes they need a transfer a lot restrictor added.
 
Maybe I missed something. Why not reduce primary main jets to 70?

I'm almost certain I am not into the primary circuit yet, foot is barely in the pedal. I went from a 74 to a 72 and saw no change, willing to try it though

You need to watch closely as to when it is rich. On my carbs, the transition from the idle circuit to main jets is 2300-2500 rpm. If you are rich below that, then put in smaller ifr's. Mine always end up at 29 or 30's, and I change all 4 together. If you are rich above the transition, then go with smaller main jets.

I will do a bit more testing and see if I can find that point, it seemed to be around 12 anywhere between 2000-3000, motor isn't really happy cruising below 2000

Do you have a stock PCV valve? It would be open with that huge cam & admitting a lot of air, could be why t/blades are able to be closed down.

Your first comment made me think about the PCV valve, the pn on the valve is 2072 (looks like GM from a quick google search) Does it make sense that at idle (6" vac) the valve is open allowing more air to come in and leaning out the idle mix, then at cruise (15" vac) with the valve closed more it's creating the rich condition? Maybe I need to try an adjustable PCV valve

What the air fuel at off idle cruise? Did you try jetting the primary’s down to see if it helps? A lot depends on where the main circuit takes over. If you need to lean the cruise prior to the boosters being on the IFR,IAB play into that. But, if the idle is good and you have good adjustment on the idle screws sometimes they need a transfer a lot restrictor added.

Sorry but just to make sure I'm answering correctly is off idle cruise foot just barely in the pedal maintaining speed on level ground? If so it's at roughly 12.0 AFR, it jumps around a little bit, anywhere from 11.8 to 12.3
 
I think you should try some smaller idle jets first. What is the A/F at idle?
 
I'm almost certain I am not into the primary circuit yet, foot is barely in the pedal. I went from a 74 to a 72 and saw no change, willing to try it though



I will do a bit more testing and see if I can find that point, it seemed to be around 12 anywhere between 2000-3000, motor isn't really happy cruising below 2000



Your first comment made me think about the PCV valve, the pn on the valve is 2072 (looks like GM from a quick google search) Does it make sense that at idle (6" vac) the valve is open allowing more air to come in and leaning out the idle mix, then at cruise (15" vac) with the valve closed more it's creating the rich condition? Maybe I need to try an adjustable PCV valve



Sorry but just to make sure I'm answering correctly is off idle cruise foot just barely in the pedal maintaining speed on level ground? If so it's at roughly 12.0 AFR, it jumps around a little bit, anywhere from 11.8 to 12.3

How far out are the idle screws? If they’re more than a turn out I’d leave the IFR alone and add transfer slot restriction. What’s the IAB size?
 
I think you should try some smaller idle jets first. What is the A/F at idle?

I have some 29s I can try. A/F at idle once warm is 13.0-13.3

How far out are the idle screws? If they’re more than a turn out I’d leave the IFR alone and add transfer slot restriction. What’s the IAB size?

Idle screws are 1.5 turns out, I think I can lean them out a bit more though, I had them at 1.25 out which brought the idle up slightly but cold start was a bit hard so moved them back, however it was pretty cold out that day so might be able to put them back to 1.5

IAB are 75, how do I add transfer slot restriction?



I am currently out of town so won't be able to mess with it until this coming weekend.
 
Plug the PCV & see what difference it makes. A correctly working PCV is about 3 cfm of the approx 17-21 cfm consumed at idle. If the PCV is not closing because of poor vacuum, it will add a LOT more than 3 cfm....
Another test is to feel the valve engine running. If it is vibrating, vac is too low. This is not a definitive test though.
 
I have some 29s I can try. A/F at idle once warm is 13.0-13.3



Idle screws are 1.5 turns out, I think I can lean them out a bit more though, I had them at 1.25 out which brought the idle up slightly but cold start was a bit hard so moved them back, however it was pretty cold out that day so might be able to put them back to 1.5

IAB are 75, how do I add transfer slot restriction?



I am currently out of town so won't be able to mess with it until this coming weekend.

You need to add a 10-32 brass set screws. You use that to shrink the passage to the transfer slot. Very common modification. 4150’s I usually start around .078 and work from there. You will need a numbered drill set as well. Harbor freight has them reasonably. See pic below, inner hole. That will lean that low speed cruise.

C1C97291-DF77-4C44-BEBB-78633C6D741B.jpeg
 
I have a bottoming tap and some set screws coming but today I swapped the 31 idle restrictors for 29s and it seemed to help quite a bit, idle A/F ratio is now around 14.2 (up from 13.0) and cruise is now at about 13.5 (up from 12.3). I also cracked the secondary throttle blades open a bit more and closed the primaries to keep the idle around 900, adjusted each about 1/4 turn. That seemed to help getting it a bit leaner. I need to pull the carb off and see where I'm at on the transfer slots, I'm sure the primaries are less than square now and I'm pretty certain the secondaries still wont be showing.

On the PCV valve pulling it didn't seem to make a huge difference in manifold vac, I did order an adjustable PCV valve, we'll see how that helps once it comes in and I get it installed.

One thing I am thinking about now is if I should get a new distributor with vac advance. Any opinions on this? Mainly street driven car that will get taken on some longer trips.
 
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