Fuel Recommended Carb Size?

Motorsport71 · Nov 25, 2020

So I have an '85 Mustang GT with a 302 automatic and 3:73 gears. I replaced the engine with a roller motor I purchased from Blueprint Engines. The dyno sheet that came with the engine showed 9:1 compression, 308 hp and 344 ft/lb torque (at the crank). I put a Holley 4160 600cfm with vacuum secondary's on it some time ago but I've had a stumble on hard acceleration. Timing is set properly. I had a shop verify it's correct. He's super busy so he can't get me in until the spring for an all around 'tune'. I was parked across the street from a guy who works on only vintage cars. An employee of his came over to look at the car (I had the hood up and he was a foxbody guy too) I mentioned the stumble and he said to go see his boss. Long story short he said right off the bat that its not getting enough fuel on takeoff. So I have a couple of options. I can take the car to him and have my carb refitted with bigger jets etc, or I can change the carb all together.

Would I be better to go with a something like a double pumper vs the vacuum secondary?
Would I benefit from a larger carb like a 650 or maybe bigger?

Thanks for looking,
Motorsport71

CarMichael Angelo · Nov 25, 2020

Motorsport71 said:
So I have an '85 Mustang GT with a 302 automatic and 3:73 gears. I replaced the engine with a roller motor I purchased from Blueprint Engines. The dyno sheet that came with the engine showed 9:1 compression, 308 hp and 344 ft/lb torque (at the crank). I put a Holley 4160 600cfm with vacuum secondary's on it some time ago but I've had a stumble on hard acceleration. Timing is set properly. I had a shop verify it's correct. He's super busy so he can't get me in until the spring for an all around 'tune'. I was parked across the street from a guy who works on only vintage cars. An employee of his came over to look at the car (I had the hood up and he was a foxbody guy too) I mentioned the stumble and he said to go see his boss. Long story short he said right off the bat that its not getting enough fuel on takeoff. So I have a couple of options. I can take the car to him and have my carb refitted with bigger jets etc, or I can change the carb all together.

Would I be better to go with a something like a double pumper vs the vacuum secondary?
Would I benefit from a larger carb like a 650 or maybe bigger?

Thanks for looking,
Motorsport71

If the car is just experiencing an initial stumble when you mat the pedal, it’s just a simple pump squirter upgrade.
If the guy is worth his salt and can truly make the carb work based on the plethora of tuning options there are for a Holley carb, then let him do it. There really isn’t any carb that youre gonna put on any engine that’ll be perfect right out of the box, but a mild hesitation during acceleration is an easy fix.

Motorsport71 · Nov 25, 2020

CarMichael Angelo said:
If the car is just experiencing an initial stumble when you mat the pedal, it’s just a simple pump squirter upgrade.
If the guy is worth his salt and can truly make the carb work based on the plethora of tuning options there are for a Holley carb, then let him do it. There really isn’t any carb that youre gonna put on any engine that’ll be perfect right out of the box, but a mild hesitation during acceleration is an easy fix.

Thank you. That's what i'll do then. He's been around forever and has a good reputation. Thanks again.

General karthief · Nov 25, 2020

Are you running an auto or stick trans? I'm guessing a stick, just curious really, the holley carb is (was) one of the most 'tuneable' carbs out there and they have several videos on their website that helps with common issues, I do agree with Mike that the squirter needs looked at, sometimes it's an adjustment, sometimes a bigger one is needed.

CarMichael Angelo · Nov 25, 2020

General karthief said:
Are you running an auto or stick trans? I'm guessing a stick, just curious really, the holley carb is (was) one of the most 'tuneable' carbs out there and they have several videos on their website that helps with common issues, I do agree with Mike that the squirter needs looked at, sometimes it's an adjustment, sometimes a bigger one is needed.

He says its an auto, stop guessing

General karthief · Nov 25, 2020

CarMichael Angelo said:
He says its an auto, stop guessing

Yeah, I even went back and skimmed over the post and still missed it not that many GT autos out there.
And yes my idiot light is shining brightly!!!!

7991LXnSHO · Nov 25, 2020

Do not go for a double pumper on the street. This carb should be easily adjusted to be very enjoyable on the street - plenty of power and better mileage. It will be easier to fix than this stuck italic font. A quick change vac secondary spring kit it worth the $ if you do not have one. That will tune how many CFM is used based on engine demand. A double pumper will open all the way and compensate with an extra accelerator pump snd more fuel.
Besides the pump size and squirter size, there is a pack of pump cams and A/B holes to mount them in that make different accelerator pump shots. It just takes some reading and experimentation.

Edit: the bar at the top works today!!! Italics are gone.

Wayne Waldrep · Nov 27, 2020

7991LXnSHO said:
Do not go for a double pumper on the street. This carb should be easily adjusted to be very enjoyable on the street - plenty of power and better mileage. It will be easier to fix than this stuck italic font. A quick change vac secondary spring kit it worth the $ if you do not have one. That will tune how many CFM is used based on engine demand. A double pumper will open all the way and compensate with an extra accelerator pump snd more fuel.
Besides the pump size and squirter size, there is a pack of pump cams and A/B holes to mount them in that make different accelerator pump shots. It just takes some reading and experimentation.

Fixed.....lol.

General karthief · Nov 28, 2020

Wayne Waldrep said:
Fixed.....lol.

I didn't have an issue with the stuck italic font, I just read it with a british accent

Monkeybutt2000 · Nov 28, 2020

Motorsport71 said:
So I have an '85 Mustang GT with a 302 automatic and 3:73 gears. I replaced the engine with a roller motor I purchased from Blueprint Engines. The dyno sheet that came with the engine showed 9:1 compression, 308 hp and 344 ft/lb torque (at the crank). I put a Holley 4160 600cfm with vacuum secondary's on it some time ago but I've had a stumble on hard acceleration. Timing is set properly. I had a shop verify it's correct. He's super busy so he can't get me in until the spring for an all around 'tune'. I was parked across the street from a guy who works on only vintage cars. An employee of his came over to look at the car (I had the hood up and he was a foxbody guy too) I mentioned the stumble and he said to go see his boss. Long story short he said right off the bat that its not getting enough fuel on takeoff. So I have a couple of options. I can take the car to him and have my carb refitted with bigger jets etc, or I can change the carb all together.

Would I be better to go with a something like a double pumper vs the vacuum secondary?
Would I benefit from a larger carb like a 650 or maybe bigger?

Thanks for looking,
Motorsport71

Curious,did Blueprint state what carb was used when it was dynoe'd?

Fuel Recommended Carb Size?

Motorsport71

Member

CarMichael Angelo

my rearend will smell so minty fresh,

Motorsport71

Member

General karthief

wonder how much it would cost to ship you a pair

CarMichael Angelo

my rearend will smell so minty fresh,

General karthief

wonder how much it would cost to ship you a pair

7991LXnSHO

wanna catch the space herp

Wayne Waldrep

Before I post a pic, do you have one of yours?

General karthief

wonder how much it would cost to ship you a pair

Monkeybutt2000

Mustang Master

Similar threads

Fuel Recommended Carb Size?

Member

my rearend will smell so minty fresh,

Member

wonder how much it would cost to ship you a pair

my rearend will smell so minty fresh,

wonder how much it would cost to ship you a pair

wanna catch the space herp

Before I post a pic, do you have one of yours?

wonder how much it would cost to ship you a pair

Mustang Master

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