Prof form 750 question

[Lit549]

Can someone tell me what this means ? Next to idle air bleeds it is listed as 73/70. Does this mean that is the range of sizes to use front and back(70 thru 73)?? Or does it mean the carb has 73's front 70's rear? It is a 750 vs pro-form(Holley).. I don't have pin gauges to check sizes and they aren't numbered.

[anotheridiot]

I believe it is front and rear, even though it seems like they do not really correspond to the jet sizes. I have purchased individual pin gages on amazon where they are not too expensive, but you can probably get an air bleed kit from Holley that are marked so you can just change them

[Lit549]

I believe it is front and rear, even though it seems like they do not really correspond to the jet sizes. I have purchased individual pin gages on amazon where they are not too expensive, but you can probably get an air bleed kit from Holley that are marked so you can just change them

I've already been tuning dicking with it, I was just curious if I was suppose to stagger them? I've been just going square, same front and back.

[DanStokes]

I've already been tuning dicking with it, I was just curious if I was suppose to stagger them? I've been just going square, same front and back.

I think that's just "whatever works". You can get them dialed in on the street but if you have access to a dyno and an O2 meter it goes quicker.

[anotheridiot]

Our only experience was with the weber conversions on the 4.2 jeeps. It was always bigger jets, more air jet. I am hoping to go back to a carburetor on the big block since we have so many parts and have never proven better performance or mileage with any of the injections, so trying to learn as much as possible.

[Captain]

Webers list the Venturi bore sizes this way.
but haven't seen "Air Bleed" listed as such.

And that's a Large Carb, going on a Big Block, or going to be WOT Track Racing? Street driving is going to be tricky just off idle ?

[Lit549]

Webers list the Venturi bore sizes this way.
but haven't seen "Air Bleed" listed as such.

And that's a Large Carb, going on a Big Block, or going to be WOT Track Racing? Street driving is going to be tricky just off idle ?

Yea it's a Vacuum secondary 750 for my 383. The engine is a Smeding "extreme" 383 that dyno'd at 468hp.. I had a 680 Quick fuel on it and hated it, I ordered the 750 to see how it ran and it made a huge difference. Car drives so much better with this 750. Really the only changes I've made is one size larger rear jet and a 7.5 power valve. The ONLY issue I have had is off idle and light cruise. To explain- it was going super rich at slower cruise(20-40mph), where it's still on the idle circuit and transfer slot. It had proven very difficult to tune out the light cruise richness. Every where else it's perfect.

If I try and lean out the light cruise richness with smaller IFR's then it creates a lean stumble. I've ended up with a 31 IFR front and rear, it seems to be the best as now the light cruise only goes to around 12.7:1 afr, it was in the 11's with the supplied 32 IFR's. I also ended up with a red pump cam/31 size pump nozzle.

[anotheridiot]

Yea it's a Vacuum secondary 750 for my 383. The engine is a Smeding "extreme" 383 that dyno'd at 468hp.. I had a 680 Quick fuel on it and hated it, I ordered the 750 to see how it ran and it made a huge difference. Car drives so much better with this 750. Really the only changes I've made is one size larger rear jet and a 7.5 power valve. The ONLY issue I have had is off idle and light cruise. To explain- it was going super rich at slower cruise(20-40mph), where it's still on the idle circuit and transfer slot. It had proven very difficult to tune out the light cruise richness. Every where else it's perfect.

If I try and lean out the light cruise richness with smaller IFR's then it creates a lean stumble. I've ended up with a 31 IFR front and rear, it seems to be the best as now the light cruise only goes to around 12.7:1 afr, it was in the 11's with the supplied 32 IFR's. I also ended up with a red pump cam/31 size pump nozzle.

at least you have the lean and rich figured out. So many of us kept wanting more fuel when it was already too rich.Only thing that ever seemed to work was adding a set screw at the rear throttle plates so you can bleed some air thru the back instead of having them closed. We were getting somewhere changing the springs in the vacuum secondaries, at least to the point of getting lean pop when they opened and actually feeling what lean was.