Correct jet sizes for Speed Demon 750 VS

[fmahannah]

I bought a new speed demon 750 VS and can't seem to get it tuned correctly. It had a quick fuel power valve n it out of the box so I suspected it might have been a return, but Holley said they use QF parts when building them since they are interchangeable.

But now I see the main jets are 74's? Holley site says in specs they should be 68's. Other sites I found with specs of 70 or 72.

Does anyone know what size primary and secondary jets should have been in an SPD-750-VS out of the box? Holley has not answered this question for me yet. I want to reset carb to factory settings and then start the tuning process over again.

Thanks, this forum has been a big help to me with my 63 Polara

 

[Shorthorse]

 

[fmahannah]

Actually Summit is sending me a new carb. Holley tech showed that the one they sent me was from before Holley even acquired demon carbs, had no numbers on it under air cleaner gasket, had a quickfuel vac pod, wrong jets, etc. If this carb is not right I am done with demon but can really use the idle eze feature

And holley tech says these are the correct specs from their page for that carb, not the ones summit is showing. I am not sure who to believe?

Barrels 4
Billet Color Shiny
Booster Down Leg
Brand Demon
CFM 750
Choke Electric
Circuit 2
Emission Code 3
Finish Shiny
Fuel Gasoline
Fuel Inlet Dual
Fuel System Carbureted
High Speed Air Bleed 28
Idle Air Bleed Size 70
Material Aluminum
Model 4160 Vacuum Secondary
Primary Main Jet 68
Primary Power Valve 6.5
Primary Pump Nozzle Size 31
Product Type Carburetor
Secondaries Vacuum
Secondary Main Jet 78
Supercharged Application No
Throttle Bore 1.688 inch
Part Number SPD-750-VS
Barrels 4
Billet Color Shiny
Booster Down Leg
Brand Demon
CFM 750
Choke Electric
Circuit 2
Emission Code 3
Finish Shiny
Fuel Gasoline
Fuel Inlet Dual
Fuel System Carbureted
High Speed Air Bleed 28
Idle Air Bleed Size 70
Material Aluminum
Model 4160 Vacuum Secondary
Primary Main Jet 68
Primary Power Valve 6.5
Primary Pump Nozzle Size 31
Product Type Carburetor
Secondaries Vacuum
Secondary Main Jet 78
Supercharged Application No
Throttle Bore 1.688 inch
Part Number SPD-750-VS

 

[Shorthorse]

You're right, what little info I could find showed 3 different specs. I guess they just changed the base unit over the years. Since your carb is new, I'd go with what Holley says.
It's been about 12-14 years ago but the original Barry Grant Demon carbs (before Holley) had some quality control issues. I was warned about this by several people after I bought a new one many years ago so I decided to take my new Demon completely apart. Sure enough there were metal shavings, there were drilled holes with metal shards still attached and one of the vacuum ports was clogged with sealer. After addressing those issues the carb preformed flawlessly for years and was still working fine when I sold the car.
I don't know what has been done about those issues, either by Demon or Holley in the time that has passed. Hopefully, that has been addressed.

 

[fmahannah]

Yes I also read about the issues with needing to clean and inspect demons before actually running them. This one was not bad inside but I am pretty sure at least one person had the carb and changed jets and other things before I even got it. It was like it was assembled using spare parts from both Demon and Quickfuel. New carb from Summit is supposed to come tomorrow and hopefully it will have all the right parts inside. Honestly I think the one I got had some internal defect because it would not run right over 50 mph no matter what I changed