First drive of 2012 with the following changes:
Swapped FBO ECU for MSD Steet Fire ignition box
Swapped old FBO dist for FBO dist with VA
Cool Carb heat shield


Last year, I finished up with A/F readings from 30mph to 60mph in the 14.2-14.6 range. 3500/4000rpms was consistant at 14.2. 50mph-WOT showed rich spike into the low 12's and then my WOT shift points leaned out a little to 12.6. My cruise to decel showed rich into the 12's. A couple of you suggested swapping to a vacuum advance distributor and that leaned out the cruise to decel A/F reading into the upper 13's.

My main goal this year is to get my 30-60mph cruising into the mid 14's to low 15's. I also want my WOT shift points around the 12.8/13.0 range.


I got two test drives in today in 65 degree weather. Once I retuned the carb to 13.6/13.8 in D, then I took notes at the following mph.
30:14.2
40:14.6-15.2
50:14.6/14.8
60:14.0
3500/4000rpms: 13.8
50-WOT: spiked to low 12's then leaned out to 12.8/13.2 at shift point
Light accel mid to upper 13's
Heavy accel high 12's

Something made my numbers go rich and my idle at a stop was acting up. When I got home I found my rear float WAY too high and it ended up have a piece of crud in it. I opted to change the primary jets from 62's to 60's and my pvcr's from .065" to .069's. I mainly wanted to lean out my cruising just a tad more and lean out my 3500/4000rpms into the 14's.

My second test drive showed the following changes after retuning my in D A/F to 13.2/13.4:
30: 14.2
40: 14.6-14.8
45: 15.4-15.8
50: 15.2-15.6
60: 14.4
3500/4000rpms: 14.2
50-WOT: No rich spike, A/F went directly to 13.0 and stayed at 13.0 until shift point
Light accel 13.8-14.2
Heavy accel low to mid 13's

I like most of what is shown above except for the readings leaner than 15.4 which gave me some slight surging. I am going to swap out my .065" IAB's for some .060"'s to see if it will richen up the 45-50mph cruise just a touch. The car loves the extra timing at idle (was 24, now 32 with VA hooked up to manifold vacuum) and it idles much smoother in the 13.2/13.4 range in D with foot on the brake (like at a stop).

Carb Review: QF SS-750-Annular Double Pumper: 60/80 jets, .031 IFR's, .065 IAB's, 10.5 HFPV/.069 pvcr's, 60% secondary linkage delay, fuel level 1/3 up the sight glasses.

Hi Dave,

Don't know if you're still having trouble with the mixture leaning out before the PV kick in.
But like Davenc was saying, that might be the cause of the 0.039 HSAB's you're running. Standard HSAB's are much smaller at 0.033.
A too large HSAB leans out the mixture at higher flows.

Have a look at this graph.
Pics are always clearer than words.;)


So you might have to go with smaller HSAB's to keep it from going lean at medium acceleration.
The lean mixture should also show up at cruise with higher loads or rpm.

Frederick,

""Don't know if you're still having trouble with the mixture leaning out before the PV kick in.""

Not anymore. The first two drives looked really good except for the cruising went lean on me after the latest jet change. I decided to just richen up the front IAB's and then see if that changes the A/F ratio enough to get me back down to the low 15's. I only need to take out about .5 on the gauge (between 40mph and 50mph). If it does not, then I will even it out and change the rear IAB's too.

My light and medium acceleration looks good. Medium is in the mid 13's and light is right around 14.0. When my pv is open (10.5 HF), the .069" pvcr's look like a good combo with the leaner main jets.

""A too large HSAB leans out the mixture at higher flows.""

That is what I found when I swapped out the stock HSAB's. I have already made two HSAB changes, and each time my 60mph+ A/F leans out a little at a time. Since my A/F numbers from 60-75mph are in still in the 14.2 range, I am considering leaning out my .039 HSAB's again . I would really like to get the 60mph+ into the upper 14's.


Once I get the 40-50mph richened up a tad, then I will test some on the HSAB's.

Thanks for the response.

Just out of curiosity, what size did you go to on the front HSABs?
I'm also experiencing lean out at medium acceleration, AFR goes to around 16 before the PV kicks in. I'm considering going with smaller bleeds; just the opposite of where you're going.

But won't know more 'till I replace the sinking float.

What rpm is 60-75rpm?

So far, all of my HSAB's have been the same. I have tried .033's, .036's and now the .039's.

""I'm also experiencing lean out at medium acceleration"".

What front pump cam and squirter combo are you running?
I am running red/.037 on the front and that gives me the mid 13's from cruising speeds to medium accel.

My 60-75mph is 3000rpms to 3600rpms.

Pink cam and 0.031" squirter.
But the lean condition is after the accelerator pump.

That pink cam should last most of the throttle position. That is a loooong duration cam. Try testing a red or an orange cam to see if you see any changes.

Ok will try to see if that cures it.
But like I said this is after the pump shot.

No it is not. Depending on which pump cam you are using, the pump shot will last between 50% throttle blade rotation and even up to 80% throttle blade rotation.
If you are cruising, you are only at 20-30% throttle rotation as a guess. The pink cam has the least amount of volume at 30% throttle position. As a reference, the orange pump cam has 30% more volume than the pink cam at the same 30% throttle blade rotation (depending on which pump cam chart you go by). The orange cam has allot more fuel volume and it lasts up to 70% throttle blade rotation.
To test this, with your engine off, just rotate the throttle and watch how far you have to move it until the pink cam quits shooting fuel. The pink cam is a 80% cam but it is in the middle on the volume chart, but it is very lean for most of its duration.

You misunderstand, I meant after the pump shot has phased out, it only last a second or 2.
It's after this that I'm experiencing the lean situation.
It's like this:
cruising, press throttle to accelerate and hold throttle at that position, pump shot, lean condition.

Sorry about that. Now I understand why you are going to try the richer air bleed.

Is there a certain rpm range that this happens or is it after any accel transitioning into cruise speed?

No apologies neccesary, sorry for not explaining it better the first time.


Well like I said, I've got a sinking float, so no guaranties. But when cruising at higher rpm's than before I did notice the mixture going leaner.
If I had to pick a specific rpm I would say above 3500-4000. It doesn't go as lean as when accelerating, but the trend is there.

""If I had to pick a specific rpm I would say above 3500-4000.""

From what I have tested, that is the range for the HSAB's. The last two jet changes that I made, I went leaner by 2 sizes and my 3500/4000rpm range only leaned out by .2 each time. Not allot of A/F change for 2 sizes and my lower rpm range can't go any leaner. So this rpm range is where I need to lean mine out while you are trying to go richer.
I need some small drill bits in the .045-.050" range for my next HSAB test. What size are you going to test?

I've still got the 0.031 the carb came with, so I'm going to try that first.
If I need any other size I will drill them.
Already got the blanks, much cheaper.

From what I know the jet affects the whole curve; shifting it up or down.
A bigger HSAB affects the shape of the curve; richer at lower flows, leaner at higher flows.
Like the graph I posted shows.

Just be careful it doesn't go lean at higher flows with the smaller HSABs.
Can't remember where I read it but there's a range where changing a main jet has much more effect than elsewhere.

I still like going smaller on the jets better than going with a bigger bleed even if you take bigger steps with the main jets.

"From what I have tested, that is the range for the HSAB's"
Not sure what you mean? AFAIK the HSABs have an effect upto max flow?

My testing has shown that the HSAB's affect the upper rpm range and the IAB's affect the lower rpm range.

Yes, but they also affect the shape of the curve.
They don't just shift the whole flow range leaner or richer.
Also the idle air bleeds serve a much different purpose than the HSABs. While the HSAB feeds air into the well to emulsify the fuel within the well, changing the fuel flow differently at different areas in the flow curve, the idle air bleeds are for the most part simply a vacuum leak, that controls the amount of vacuum pulling on the idle well and idle jet.

Here's another pic to clarify what I'm talking about.
http://www.innovatemotorsports.com/forums/attachment.php?attachmentid=1803&d=1177457666
D is the HSAB
A and B are the emulsion bleeds.

Thanks for the info

Y07_A66:

It looks that your target WOT AFR is 13.0. Some time ago you posted the chart that indicated that with E10 the target should be around 12.2. Do you have E0 where you live, or is there some reason you are discounting the chart? I thought it was an interesting insight when you originally posted that.

Dave,
Good catch. I am only targeting 13.0 for the short term leanest WOT reading, just like I know that my leanest safe cruise limit is 15.6.
I do not get any pinging at that 13.0 reading and then I will work my way back down into the low to mid 12's once I get the cruise back in line.

Thanks Dave