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Discussion Starter · #1 ·
I recently purchased a sbc 350 with a B&M 250 supercharger with two Holley 1850-3 dual pumper carbs. I don’t know anything about this motor or what’s been done to it as the guy died and his daughter was selling off everything in his shop. This motor was in his shop on an engine stand yet the carburetors were just sitting on top of the blower not bolted down or anything so I’m not sure if they were ever installed or modified to work with this setup.
I hooked the Motor up to an engine run stand and fired it up but I cannot get it to idle. It hovers around 1800rpm and starts to surge. My question is do I need to modify these carbs to work with a blower setup? I will just be using this as a street car and not really interested in it being super fast or anything, just would like it to be reliable.
I have never had a blower before and know nothing about them so any help would be appreciated.
 

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The 1850-3 is a basic 600 cfm vacuum secondary performance replacement carb, so it won't be set up correct for use on a draw thru supercharger. They will need a handful of modifications to work correctly.
- Powervalves need to be boost referenced.
- Vacuum secondary diaphram chambers have to be tied together using covers that have hose barbs, so both secondarys on the seperate carbs open at the same rate.
- Idle feed restrictions will need resizing.
- Bypass air holes may need to be drilled in the primary throttle plates to allow enough air through for the engine to idle but still allow you to close the main idle screw to set the correct transfer slot exposure at the edge of the throttle blades and make the idle more tuneable.
- May need higher capacity accelerator pump nozzles and larger accelerator pump cams to get enough pump shot.

They are not the best starting point for making blower carbs, but it can be done.
 

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Discussion Starter · #3 ·
The 1850-3 is a basic 600 cfm vacuum secondary performance replacement carb, so it won't be set up correct for use on a draw thru supercharger. They will need a handful of modifications to work correctly.
- Powervalves need to be boost referenced.
- Vacuum secondary diaphram chambers have to be tied together using covers that have hose barbs, so both secondarys on the seperate carbs open at the same rate.
- Idle feed restrictions will need resizing.
- Bypass air holes may need to be drilled in the primary throttle plates to allow enough air through for the engine to idle but still allow you to close the main idle screw to set the correct transfer slot exposure at the edge of the throttle blades and make the idle more tuneable.
- May need higher capacity accelerator pump nozzles and larger accelerator pump cams to get enough pump shot.

They are not the best starting point for making blower carbs, but it can be done.
The 1850-3 is a basic 600 cfm vacuum secondary performance replacement carb, so it won't be set up correct for use on a draw thru supercharger. They will need a handful of modifications to work correctly.
- Powervalves need to be boost referenced.
- Vacuum secondary diaphram chambers have to be tied together using covers that have hose barbs, so both secondarys on the seperate carbs open at the same rate.
- Idle feed restrictions will need resizing.
- Bypass air holes may need to be drilled in the primary throttle plates to allow enough air through for the engine to idle but still allow you to close the main idle screw to set the correct transfer slot exposure at the edge of the throttle blades and make the idle more tuneable.
- May need higher capacity accelerator pump nozzles and larger accelerator pump cams to get enough pump shot.

They are not the best starting point for making blower carbs, but it can be done.
Thank you for your response.
Would it be better to start with something else or buy carbs set up already? (these are very expensive though) what would you suggest?
 

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Blower motors are not a place to learn on if you have no experience. Incorrect mixtures can fry pistons faster than you can read this sentence. It would be wise to collaborate with a known carburetor specialist. Convenient if you live in such an area like LA, Houston, etc.

Bogie
 

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Thank you for your response.
Would it be better to start with something else or buy carbs set up already? (these are very expensive though) what would you suggest?
It would depend on your familiarity with carburetors and whether you can handle small drilling and maybe some small thread tapping, but if you can manage that then a $200-300 in upgrade parts and rebuild kits you can get the pair of 600 Vacuums you've got to do the job and do it yourself.

If not, then buying a pair ready-to-go would be your best bet.

You're just going to have the wrap your head around the fact that you are going to have to spend $1000-1500 for a pair of carbs....
Welcome to Supercharging:LOL:
You wanna play, you gotta pay kind of deal if you can't do it yourself
 

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Discussion Starter · #6 ·
It would depend on your familiarity with carburetors and whether you can handle small drilling and maybe some small thread tapping, but if you can manage that then a $200-300 in upgrade parts and rebuild kits you can get the pair of 600 Vacuums you've got to do the job and do it yourself.

If not, then buying a pair ready-to-go would be your best bet.

You're just going to have the wrap your head around the fact that you are going to have to spend $1000-1500 for a pair of carbs....
Welcome to Supercharging:LOL:
You wanna play, you gotta pay kind of deal if you can't do it yourself
Thanks again.
I’m probably leaning towards buying new carbs as I could use the others for another project I have.
Would you stick with the Holley’s or get something else? Also are they pretty much plug and play or would I still need to get them calibrated/ tuned for that setup?
Thank you for your help 👍
 

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Discussion Starter · #7 ·
Blower motors are not a place to learn on if you have no experience. Incorrect mixtures can fry pistons faster than you can read this sentence. It would be wise to collaborate with a known carburetor specialist. Convenient if you live in such an area like LA, Houston, etc.

Bogie
Yeah, that’s what worries me. There is a carb place near ish to me but not sure if they are familiar with supercharger setups etc.
 

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Thanks again.
I’m probably leaning towards buying new carbs as I could use the others for another project I have.
Would you stick with the Holley’s or get something else? Also are they pretty much plug and play or would I still need to get them calibrated/ tuned for that setup?
Thank you for your help 👍
They might need some minor adjustment or rejetting, but they would get you up and running without causing problems or hurting parts. Would be a safe set-up tune in them.
Only Holley's/Holley clones for me, not Edelbrocks
 

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Discussion Starter · #9 ·
They might need some minor adjustment or rejetting, but they would get you up and running without causing problems or hurting parts. Would be a safe set-up tune in them.
Only Holley's/Holley clones for me, not Edelbrocks
They might need some minor adjustment or rejetting, but they would get you up and running without causing problems or hurting parts. Would be a safe set-up tune in them.
Only Holley's/Holley clones for me, not Edelbrocks
 

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Thank you, would you stick with the 600cfm?

really! I like the sound of that. Is the wiring easy for EFI?
Ill check into it. 👍
EFI wiring is super easy. Kits come with a harness; you just plug and play. And you can read data and make changes with the touchscreen. The fuel plumbing is the hardest part, since it takes a new electric fuel pump, regulator and fuel lines. But FAST and the others sell all the pieces; one-stop shopping.
 

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Discussion Starter · #13 ·
EFI wiring is super easy. Kits come with a harness; you just plug and play. And you can read data and make changes with the touchscreen. The fuel plumbing is the hardest part, since it takes a new electric fuel pump, regulator and fuel lines. But FAST and the others sell all the pieces; one-stop shopping.
EFI wiring is super easy. Kits come with a harness; you just plug and play. And you can read data and make changes with the touchscreen. The fuel plumbing is the hardest part, since it takes a new electric fuel pump, regulator and fuel lines. But FAST and the others sell all the pieces; one-stop shopping.
I will definitely look into that. Thanks for your advice 👍
 
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