Holley 4175 Tuning
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Joined: Dec 2006
Posts: 56
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From: Milwaukee Wisconsin
Holley 4175 Tuning
Hi Everyone-
I took my car (71 -350) in to the shop to get tuned and run on the dyno. A/F meter says the car is running too rich at WOT. My tuner says my Holley 4175 is not adjustable like most Holleys. I don't know much about carbs but the secondary jets can't be changed on a 4175? I just have a hard time believing that a carb is "not adjustable" for A/F under WOT.
Thanks in advance
I took my car (71 -350) in to the shop to get tuned and run on the dyno. A/F meter says the car is running too rich at WOT. My tuner says my Holley 4175 is not adjustable like most Holleys. I don't know much about carbs but the secondary jets can't be changed on a 4175? I just have a hard time believing that a carb is "not adjustable" for A/F under WOT.
Thanks in advance
Burning Brakes
Joined: Jan 2007
Posts: 1,057
Likes: 4
From: Concord Calif
Hi Everyone-
I took my car (71 -350) in to the shop to get tuned and run on the dyno. A/F meter says the car is running too rich at WOT. My tuner says my Holley 4175 is not adjustable like most Holleys. I don't know much about carbs but the secondary jets can't be changed on a 4175? I just have a hard time believing that a carb is "not adjustable" for A/F under WOT.
Thanks in advance
I took my car (71 -350) in to the shop to get tuned and run on the dyno. A/F meter says the car is running too rich at WOT. My tuner says my Holley 4175 is not adjustable like most Holleys. I don't know much about carbs but the secondary jets can't be changed on a 4175? I just have a hard time believing that a carb is "not adjustable" for A/F under WOT.
Thanks in advance
They do not have conventional jets in the rear. But the plates do come with different size passages in them to effect different jetting needs, they are are not cheap but are available in most sizes you may need. I would look up the list number of your carb on the Holley site to see what size plate you have now. The list number is printed on the air horn usually on the drivers side front. If you know how rich your car is now you can get pretty close knowing that and not buy more than one plate. If your tinner is any good he can tell you have many jet sizes smaller you need.
Burning Brakes
Joined: Jan 2007
Posts: 1,057
Likes: 4
From: Concord Calif
The plate with changeable jets will bolt on but as far as what Holley told me it will not work on the 4175 because of channel differences. Have you actually done this? did it really work for you? And if it did work what plate did you use? And also was there a longer fuel transfer pipe you used also as the jet plates are thicker than the plate as used on the 4175.
Le Mans Master
Joined: Oct 2010
Posts: 6,914
Likes: 836
From: melbourne florida
2023 C3 of the Year Finalist - Modified
i remember now Holley discontinued that part a long time ago. that's the big issue with that Carb the float bowls that you have to take the bowls off for a float adjustment and having to drill or restrict passages........ kind of like a quadrajet!
Safety Car
Joined: Aug 2001
Posts: 3,681
Likes: 200
From: Waterford Mi
I had to replace my metering plate when I tuned mine. I bought them through my local family owned autoparts store. I bought an afr meter and played with them. Sorry, I can't remember what the final size I am using. I believe I dropped two sizes from what was in there. I also changed the power valve from the 6.5 to an 7.5 to help my mid throttle. My engine pulls 15vac so I could have gone to the 8.5. My biggest issue was with the accelerator circuit. It was way to rich. The carb came with a 40 discharge nozzle, I put in a 21 and played with different cams to dial it in. Now the air fuel ratio runs in the 13's most of the time.
