Holley 670 SA tuning with wideband

-
trebor75

trebor75

Well-Known Member
Joined
Sep 12, 2009
Messages
981
Reaction score
452
Location
Sweden
This is the combo:
1970 duster
1965 - 273 commando
Cam: Comp Cams Magnum 282S - 282/282 Lift 495/495 (solid) Beehive Springs
Edelbrock D4B intake / Holley 670 Street Avenger
Pertronix Ignitor II & Flame Thrower coil
Hooker Headers
2.5" Dual Exhaust / Super 44 Flowmaster
8 3/4 - 3.55 - SureGrip
727 auto / Shift Kit
10" 2000 stall converter
B&M Quicksilver Shifter

Yesterday a friend helped me to weld a bung for a wideband air fuel ratio gauge (Innovative LM-1). Then we took of my Holley to get a view of the transitions slots, and yes, I was to much into them. So we corrected that and started tuning the idle mixture until we had a satisfactory reading. The transition from idle is now crisp and nice. We took it out with the gauge hooked up, this is the results:
Idle: Perfect
Full throttle: Perfect
Cruising: maybe a little on the rich side
It does however get rich every time I give it gas, so It gets to much fuel from the accelerator pump shot.

Im thinking of going down in size from my 31 nozzle to a 28 (Holley recommends 3 sizes when you make a change), and also going down to 63 on my now 65 primary Jets. Does this sound like a good plan?
Also, it's hard to get over 700 rpm at idle without messing up the idle circuit by going into the transition slots to much. Any suggestions?
Some people (seen after googeling) likes to open up the secondaries a little bit at idle, why is that? Im new to tuning so please bare with me, Im exited about learning and welding that bung on there was a great thing to do :)
 

Attachments

  • LM1_Kit_3.jpg
    33.2 KB · Views: 390
Gonna go buy jets and nozzle tomorrow morning. Can any one chime in?
 
Go for a drive.

Watch the A/F meter at 500rpm steps. You'll see where the mains start to come in as the mixture will begin to richen up.

If you are rich below that point, look at the Idle air bleed/Idle feed restrictors.

Initial timing plays a big part in idle settings. Make sure you have plenty with an XS282s and a 273. More than 20 may be about right for that set up.
 
crackedback said:
Go for a drive.

Watch the A/F meter at 500rpm steps. You'll see where the mains start to come in as the mixture will begin to richen up.

If you are rich below that point, look at the Idle air bleed/Idle feed restrictors.

Initial timing plays a big part in idle settings. Make sure you have plenty with an XS282s and a 273. More than 20 may be about right for that set up.
Click to expand...

Thanks
 
Dunno what A/F ratio you are trying to hit for acceleration. Read up on the A/F ratio for acceleration; being a lot richer(lower A/F ratio) than for static/cruise levels is normal and necessary. Google 'Air/fuel ratio during acceleration'

And be careful to not get hung up on the numbers.....SOP (seat of the pants) feel is an important part of the tuning too.
 
The thing with secondaries..........this is to allow some air in instead of through the primaries, so that the primary butterflies will be further closed at the same idle speed. This is to keep the idle transfer slots in proper position with a hotter cam, which otherwise, would require the primary blades to be too far open.

Years ago, some used to preach drilling small holes in the primary blades

Also, get your timing and advance curve "settled" before you screw with carburetion
 
Thanks for the responses. I tune for performance and not milage and SOP is just as important as the numbers. My initial ignition and total has been tuned before messing with the carb. It wants as much as 23 initial, it doesn't kick back and I have locked the total to 35. I could probably go even more on the initial.

Primary jet - 65
Secondary - 68

Pump nozzle - went from 31 to 28 today. Got better numbers but could not really tell any difference in performance.

Problems I have ran into while tuning
- It's hard to get it to idle decent (it's to low) without messing up the transition from idle to part throttle by turning the curb idle screw to much. It now has a crisp response but idles like 600 rpm and is very loopey with the big cam.

- At WOT it takes off hard and then has a slight hesitation and then it takes of again and when it shift to 2 gear it chirps the tires. I have the heavy brown spring in the secondary vacuum right now, only black is heavier. Is it the pump shoot that kills it by draining the engine? Could I have gone to lean on the idle mixture? Wrong spring? I guess I just have to keep tuning. Enough for today though.

Any suggestions on these problems?
 
How much rich on the cruise does it go?

One thing I found with basically the same setup (Edlebrock carb though) is that you can get somewhat leaner on the idle mixture than 14.7 without a lot of complaining from the engine.
This will bring down the cruise A/F a little leaner.
You wouldn't however want to try to get away with that at WOT due to leaner mixtures causing more heat.

Another important detail that probably wont apply to you because your WOT was already withing range is that when you go leaner you have to be a bit carefull of preignition (leaner makes it happen easier)

One thing that may or may not be related to your specific location is that I frequently drive down to Phoenix where the elevation in 2,000+ feet lower, so I left my cruise mixture a hair rich (like around 13.5 - 14 to one) so it doesn't tend to run too lean and get hot easier because of it.
This time of year it gets in the 106-112 range down there.

Just thoughts.
 
TrailBeast said:
How much rich on the cruise does it go?

One thing I found with basically the same setup (Edlebrock carb though) is that you can get somewhat leaner on the idle mixture than 14.7 without a lot of complaining from the engine.
This will bring down the cruise A/F a little leaner.
You wouldn't however want to try to get away with that at WOT due to leaner mixtures causing more heat.

Another important detail that probably wont apply to you because your WOT was already withing range is that when you go leaner you have to be a bit carefull of preignition (leaner makes it happen easier)

One thing that may or may not be related to your specific location is that I frequently drive down to Phoenix where the elevation in 2,000+ feet lower, so I left my cruise mixture a hair rich (like around 13.5 - 14 to one) so it doesn't tend to run too lean and get hot easier because of it.
This time of year it gets in the 106-112 range down there.

Just thoughts.
Click to expand...

Thanks for the thoughts. After todays tuning I'm within limits on cruising now. I rather be a little on the rich side side just as you mention. The things I'm trying to achive is as I explained in my latest post:

Primary jet - 65
Secondary - 68

Pump nozzle - went from 31 to 28 today. Got better numbers but could not really tell any difference in performance.

Problems I have ran into while tuning
- It's hard to get it to idle decent (it's to low) without messing up the transition from idle to part throttle by turning the curb idle screw to much. It now has a crisp response but idles like 600 rpm and I want it to idle at at least 800 rpm.

- At WOT it takes off hard and then has a slight hesitation and then it takes of again and when it shift to 2 gear it chirps the tires. I have the heavy brown spring in the secondary vacuum right now, only black is heavier. Is it the pump shoot that kills it by draining the engine? Could I have gone to lean on the idle mixture? Wrong spring? I guess I just have to keep tuning. Enough for today though.
 
I gottcha.
Of course you watched your A/F mixture while it fell on it's face?
What did the guage say when it did that?
 
Don't get to hung up on keeping the transition slot at .040 or very small,
You can open the throttle more if the engine idles clean, the mixture screws still have input, and your not starting to draw through the boosters ... you'll be fine.
 
EL5DEMON340 said:
Don't get to hung up on keeping the transition slot at .040 or very small,
You can open the throttle more if the engine idles clean, the mixture screws still have input, and your not starting to draw through the boosters ... you'll be fine.
Click to expand...

X2
Sorry, I got stuck on the performance problem.
 
You must log in or register to reply here.
-

Back
Top