Most probably your 750 just needs some tuning. You didn't mention which 750 you have, but I just swapped a Holley 4160 series 750 DP for a 4150 series 750 -HP. The difference in the 4160 and 4150 is the 4160's do not have replaceable secondary jets - they have a metering block. 4150's are more like the original everything's adjustable Holley's, and are really more to my liking.
My 4160 had vacuum secondaries, electric choke, and non-replaceable secondary jets. My new 4150 has mechanical secondaries, no choke and fully replaceable jets, power valve, accelerator pump, squirters, etc. etc. The difference is the 4160 is about $260, while the 4150 is $600....big difference, indeed, but the 4150 is bar far the better carb.
Used to run too rich with the 4160, but since I couldn't make adjustments I had to live with the fumes. WIth the 4150 series, I'm running #70 primaries, and #72 secondary jets. The 'fumes' you mentioned are all but gone...and the car really comes on like gangbusters! Everyone said my gas mileage would go to hell with the mechanical secondaries, but I figured what the hell, this ain't no Corolla and I really don't give a flyin' flip about gas mileage in a Cobra...who does? So far, I've been very pleased with the changeover and wonder why more folks don't just go to the 750-HP right on the front end. Sure, it's more expensive, but if you're looking to not spend a lot of money, brother are YOU in the wrong hobby.
The Holley 750-HP seems perfect for my stroked 351... Tastes great, less filling....what more could I ask for?
