Quick Fuel SS-750-AN Wideband Tuning

[frederick]

Finally found some time to post the details.
Sorry it took so long, Gunmetal.

The carburetor in question is the Quick Fuel SS-750-AN, like the title says.
Basically a Holley clone with annular boosters.

Had some trouble with incorrect jetting from the factory, but that was taken care of swiftly.
My carb had 70 IAB, 31HSAB and one 88 secondary jet.
The card that came with it said it should have 71IAB, 33HSAB and 2 82 secondary main jets.

The SS-750-AN should have:
68 Primary Mains
82 Secondary Mains
71 IAB
33 HSAB
31 Shooters
0.033 IFR
0.060 PVCR
6.5 PV
110 Needle and seat



Now for the wideband testing.
I'm using an Innovate LM-1.
I haven't used the logging capability, but just kept a constant RPM and read the AFR from the screen.




Idea is to get the off-idle circuit right first.
1. As you can see I started with the wrong IAB and HSAB. (70 and 31)
Didn't take exact notes, but is was very rich, less than 12 everywhere.
2. Reduced the IFR and povervalve , better, but still too rich.
3. Changed the IAB and HSAB to what they should be.
AFR's much better now.
4. Further reduced the IFR.
Haven't tested yet.


F.

[GunMetal]

Good stuff Frederick . Yeah, I haven't got into my carb yet. Busy with the family / work / life stuff. I'll be monitoring your progress as you post. Best of luck Steve

[firefighter3931]

Good work Frederick 

I Like tune #2 with mid-high 12's AFR 


Ron

[YO7_A66]

Frederick,
I have been using the SS-750-AN on my 340 for about two years now but just in the past 2 months I have been tuning with a FAST A/F wideband kit.
My carb came just like your card showed and I found it extremely rich out of the box. I was surprised because I bought it directly from QF and I discussed my setup with a tech.
I knew when I bought it that it was rich and over the two years I made my own changes and now I am tweaking it with the wideband.
From my wideband testing, I found the transition circuit is handling the cruising speeds all the way up to about 3500rpms (70mph) now that I have changed out the stock HSAB's from .033 to .036". I wanted to stay on the transition circuit thru 70mph and the stock .033" pieces were allowing the mains to start around 3100rpms (60mph).

When I started with the wideband, I had .028 ifr's and 66 main jets which was making the cruising speeds (25-60mph) lean to very lean, showing in the 15.6 to 17.0 range. I then swapped out the .028's for some .031's and now my cruising shows 14.2 to 15.2 range. My main circuit starts around 3500rpms which is giving me 13.8 with 64 main jets, and 4000rpms is giving me 13.6 reading. I now have 62 main jets and I need to test this setup this weekend. With the 64 main jets and 75 secondary jets, my cruise to WOT A/F reading was showing 13.0 at my shift point. I have not started on the secondary jetting yet but once I test the 62's up front, then I will finish up on the secondary jetting along with the secondary pump setup.

For your reference, this is my current carb setup with a mild 340.
62/75 jets, 8.5 "standard" power valve, .071 IAB's,  .036" HSAB's, black/.037 primary and black/.031 secondary, 40% secondary linkage, .031 IFR's,.

The engine idles best with an in gear idle A/F around 13.4-13.6. I will be aiming for a cruise to WOT A/F around 12.8-13.2 once I get a little farther in my tuning. I am currently tuning the light acceleration A/F in the 13.4-13.6 range.

This carb has been very easy to tune. So far everything that I have had to change to meet the A/F ratio, the carb has had a jet or an adjustment that has made this tuning project very easy.

Dave

[frederick]

Hi Dave,

Thanks for the reply.
I've been following the thread on moparts with interest.

I have not done much tuning since my last reply. -Too many projects and bad weather.
Only done one session:


Short WOT run showed an AFR of 13.0, so perhaps a bit too lean.

Idling at 13.1
A thing I must have missed before is that it goes very lean just above idle, 1200rpm
At 1500 its back to 13.8?
Not sure how I'm going to tackle that yet. Have you got any suggestions?


My next step will be to very slowly increase the rpms, logging rpms and AFR.
And to watch the primary booster, to see when it starts dripping.


"From my wideband testing, I found the transition circuit is handling the cruising speeds all the way up to about 3500rpms (70mph) now that I have changed out the stock HSAB's from .033 to .036". I wanted to stay on the transition circuit thru 70mph and the stock .033" pieces were allowing the mains to start around 3100rpms (60mph)."
Not sure I understand what you're saying?
I thought the IAB was controlling when the transition circuit stops?

I agree on the carb, I had a Edelbrock 600 on it before and this is miles better.

My engine is a mild 383.
Lunati Voodoo cam 262/268 @0.050"  0.475"/0.494" Lift
9.5 Compression
1.75"Headers
Aluminium 440 Stealth heads


Again thanks for the reply,

Frederick
(my next reply will take a while as I'm leaving for a two week holiday tomorrow.)

[YO7_A66]

  Frederick,

I was not sure if you have seen that thread or not. I sure have received some great advice.

""Short WOT run showed an AFR of 13.0, so perhaps a bit too lean.""
- Maybe, but what I have read, 12.8 to 13.2 is a good starting range.

""Idling at 13.1""
- Is this in Neutral or in D? I have tried 14.0-14.2 in D and the motor did not like it. It was too lean and the idle was moving around on me.  13.6-13.8 seems to be my leanest idle in gear and 13.4-13.6 is what my engine likes.

""A thing I must have missed before is that it goes very lean just above idle, 1200rpm
At 1500 its back to 13.8? Not sure how I'm going to tackle that yet. Have you got any suggestions?""
- You are actually RICH at 1200rpms (low 13's). My first thought is that your primary pump shot may need some attention. I would suggest a pump cam with a lower initial hit (pink or white) or a smaller pump squirter. Your 1000 to 1500rpm A/F shows in the 13's. I would bet that if you lower your idle A/F reading by ..4 to .6(maybe 13.5 or so), then this range would lean out for you. You would then be right about the 14.0 to mid 14's in the 1000 to 1500rpm range which is very good.

- The High Speed Air Bleed changes the timing of the main circuit. Our carbs came stock with .033" HSAB's and looking at my charts, mine mains started in around 3100rpms or so. When I changed to the .036" HSAB's, then the mains started around the 3500rpm range.

- The Low Speed Air Bleeds affect the idle and transition circuits.

- When I was looking at your above chart, I noticed on #4 & #5 that you changed jetting from 66's to 64's. When I look across your chart from 1000 thru 2500rpms, I see that your A/F numbers between #4 and #5 are fairly the same. Then when you hit 3000rpms, your A/F got leaner by .8 (13.2 to 14.0) on #5. My guess is your mains are starting in around 3000rpms like mine did when I had the stock .033" HSAB's in my carb.  You could try a set of 62 main jets and I would bet that your 3000rpms and up go leaner again which would put you in the 14.8 range. You are very close on your cruising A/F goal (apx 14.5 to 15.5).

Note: My first couple of test drives was showing me readings from 16.0-17.0 in the 1700 to 2200rpms range. I felt surging in the mid 16's so now I know my lean range. I now cruise between the 14.2 and 15.2 range but I know now that it can handle upper 15's, but for now, I am going to keep it where it is.

It does not appear that many use the SS series carbs. I was glad to see your thread so that I can compare notes. Thanks and have fun on your holiday.

Dave

[frederick]

Hi Dave,

My last post before the holidays.

""Idling at 13.1""
- Is this in Neutral or in D? I have tried 14.0-14.2 in D and the motor did not like it. It was too lean and the idle was moving around on me.  13.6-13.8 seems to be my leanest idle in gear and 13.4-13.6 is what my engine like
I've got a 4 speed manual, so neutral.
It could be a bit leaner, but then the 1200rpm leanness becomes very noticeable.

""A thing I must have missed before is that it goes very lean just above idle, 1200rpm
At 1500 its back to 13.8? Not sure how I'm going to tackle that yet. Have you got any suggestions?""
- You are actually RICH at 1200rpms (low 13's). My first thought is that your primary pump shot may need some attention. I would suggest a pump cam with a lower initial hit (pink or white) or a smaller pump squirter. Your 1000 to 1500rpm A/F shows in the 13's. I would bet that if you lower your idle A/F reading by ..4 to .6(maybe 13.5 or so), then this range would lean out for you. You would then be right about the 14.0 to mid 14's in the 1000 to 1500rpm range which is very good.
No it's really very lean at 1200. At 1200rpm AFR is 16.0. I noticed this the last time I very slowly increased the revs. I can hold it at 1200 and the AFR stays at 16.0, no misfires to explain it too.
Sorry I wasn't clearer.
So the progression it like this:
idle = 13.1 1200rpm =16.0 1500=13.8
Very odd.
Do you think a different progression slot length would make a difference?(currently set at 0.040")

Think your right about the mains coming on at 3000.
But before I'm gong to order smaller main jets, I'm going to test at higher cruise rpms to see what the AFR's are there.
(I've got the holley jet kit but they start at 64, like you undoubtedly know.)

CHeers,

Frederick

[YO7_A66]

  ""No it's really very lean at 1200. At 1200rpm AFR is 16.0. I noticed this the last time I very slowly increased the revs. I can hold it at 1200 and the AFR stays at 16.0, no misfires to explain it too.
Sorry I wasn't clearer.
So the progression it like this:
idle = 13.1 1200rpm =16.0 1500=13.8
Very odd. ""

idle = 13.1 1200rpm =16.0 1500=13.8 WOW, that is a big difference in just 300rpms. I wish that I could help you with that one. I hope someone will chime in because I am curious what that could be.

Dave