[tremo]

Originally Posted by Kenth

Very few Chevy smallblock Quadrajets flows full 750 cfm, most of them are restricted by the reduced air valve opening degree.
Only some HP units got the full 750 cfm flow.

I wouldn't count on there being original jets and rods if the mechanic who fixed the carburettor was knowledgeable.
These carburetors have .120" main air bleeds in air horn and floatbowl and the mixture would be too lean with the original jetting.
One way to still use the original jetting is to reduce the main air nozzles with .050" inserts.
Otherwise, #77-#78 jets paired with 48B-49B primary needles may suit your engine's needs with this carburetor.
There's only one way to know what's inside (or two if the mechanic has notes).

FWIW

Thanks Kenth!

- If most don't flow at 750cfm, what do you think they actually flow at (approx)? ~700cfm?

- You make a good point not to assume what the primary metering rods and jets are. My mechanic was a Pontiac-guy, so he may very well have set it up for my altitude? I was also thinking they might be stock because it's always run very rich at idle even after adjusting the idle mixture screws properly. I will see about opening the carb to check.

- Thanks for the recommendation to use #77-#78 jets paired with 48B-49B primary needles. This input is what I'm ultimately after! FYI that the car is primarily a street car, but over the last couple of years I've started to race the full season for my class (about 7 times/year) so I'd rather tune it for racing vs. street.

- So the idea is to increase the jet size (more fuel) and decrease the metering rods (less fuel)? I'm still learning how the jets work in conjunction with the the metering rods so bare with me! Note that while I live at 5,800', Bandimere is typically at ~9,000'+ density altitude during the season and even higher during 90+ degree days. Would your recommendation change given the higher density altitude?

Thanks again for all the input, very valuable!

[mchell]

Originally Posted by tremo

Thanks Kenth!

- If most don't flow at 750cfm, what do you think they actually flow at (approx)? ~700cfm?

- You make a good point not to assume what the primary metering rods and jets are. My mechanic was a Pontiac-guy, so he may very well have set it up for my altitude? I was also thinking they might be stock because it's always run very rich at idle even after adjusting the idle mixture screws properly. I will see about opening the carb to check.

- Thanks for the recommendation to use #77-#78 jets paired with 48B-49B primary needles. This input is what I'm ultimately after! FYI that the car is primarily a street car, but over the last couple of years I've started to race the full season for my class (about 7 times/year) so I'd rather tune it for racing vs. street.

- So the idea is to increase the jet size (more fuel) and decrease the metering rods (less fuel)? I'm still learning how the jets work in conjunction with the the metering rods so bare with me! Note that while I live at 5,800', Bandimere is typically at ~9,000'+ density altitude during the season and even higher during 90+ degree days. Would your recommendation change given the higher density altitude?

Thanks again for all the input, very valuable!

Unless your carb is waaaaay off, changing jet/rod combo’s is not really going to move the chains …..At those altitudes I would think you’d want it a tad lean….. I would play with timing if anything….and nitrous…. Lol