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I bought myself an early birthday present, A wideband AFR meter.
Just starting out I don't think my carb is doing to bad.
Carb is a Holley 4175 spreadbore with vacuum secondraies.
Idle is in the 12.5 range.
Cruise is in the 12.5 range any where from 45mph and above 80mph.
WOT starts out in the 12.5 and increases to around the low 14's for a short time until it gets going, I figure this is the excellerator pump circut being I have that tuned real lean. once it starts hitting the area that the secondaries open up it drops hard into the low 11's. By then I am hitting above 3500rpm's and about 75mph.
I already changed the secondary metering plate from a 54 to a 49 a couple of years ago when I had the car on a dyno and it showed the WOT to be in the low 10's.
I would like to see the cruse afr to be closer to 13.5 range. If I change the metering plate again I know that will change my WOT but to what size?
Will this effect the cruse afr or do I need to change the main jets too? If so how many sizes should I drop them, 1 or 2? I do not know what size is in there until I get a chance to take it apart.
Cruise is in the 12.5 range any where from 45mph and above 80mph.
WOT starts out in the 12.5 and increases to around the low 14's for a short time until it gets going, I figure this is the excellerator pump circut being I have that tuned real lean. once it starts hitting the area that the secondaries open up it drops hard into the low 11's. By then I am hitting above 3500rpm's and about 75mph.
I already changed the secondary metering plate from a 54 to a 49 a couple of years ago when I had the car on a dyno and it showed the WOT to be in the low 10's.
I would like to see the cruse afr to be closer to 13.5 range. If I change the metering plate again I know that will change my WOT but to what size?
Will this effect the cruse afr or do I need to change the main jets too? If so how many sizes should I drop them, 1 or 2? I do not know what size is in there until I get a chance to take it apart.
I love new toys.
Brian - NCM Lifetime Member
73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System
Dewitt radiator and dual electric fans
Borgeson Steering box
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
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Member: NCRS, NCRS Texas, Corvette Legends of Texas
Changing the secondary metering plate will have no effect on "cruize" ratio, unless you're running with the secondaries open at that speed...which would just be either weird, or illegal! 
Changing the main jets will have the most effect. My standard rule on main jets was to change two sizes up/down, depending on the results I wanted, and what the plugs were telling me. Using an AFR meter is cheating...
That's just me, tho. Others may have other ideas.
Changing the main jets will have the most effect. My standard rule on main jets was to change two sizes up/down, depending on the results I wanted, and what the plugs were telling me. Using an AFR meter is cheating...
That's just me, tho. Others may have other ideas.
Joel Adams
C3VR Lifetime Member #56 
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
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Send PMMounds View, MN - USA
Joined: 5/24/2007
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Vette(s): 70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe
The theoretical ideal for cruising and idle is 17.6, and for WOT is about 12.5. The new EZ EFI tunes to those numbers, and makes exactly as much horsepower as a carefully tuned carb on the dyno.
Larry
Larry
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Thanks Larry for the numbers, I will be happy with cruise to be in the 13.5- 14 range.
Joel, I know the metering plate wwill only effect WOT and no I hope that aint happening when I am just cruisng around. As a matter of fact i don't thinkl I ever see WOT except when I am playing with the AFR meter. Hopefully I can dive into the jets this week and learn some more.
When I am done I can add this to the things I know just enough about to get me in trouble, I all ready gots lots of that stuff all ready.
Brian - NCM Lifetime Member
73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System
Dewitt radiator and dual electric fans
Borgeson Steering box
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in Forum: C3 HVAC, Fuel, Emissions, and Exhaust
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