While somewhat “un-scientific” you’ve done something that a lot of hot rodders have done over the years, i.e., “open-things-up-a-bit!” While not recommended by Holley, it sounds like it helped you identify the issue and perhaps point toward a resolution.

The stock main metering jets for a 650 Holley (4150) are typically number(s) 67 on the front and 73 or 76 on the rear. Where a 49 came from is beyond me - - the smallest factory jets from Holley on any of their four barrels (that I’m aware of) is a 60. A 49 is pretty small!

Bear in mind that the number doesn’t always equal the hole size, e.g., a 49 is actually a .048” jet. The 72 is .075” and so on.

Part numbers for Holley jets are easy – they’re 122-xx, where xx = the Jet Number. You could buy a bunch of individual sets to try ($7.00 a pair), i.e., 122-66, 122-67 (front) and 122-71, 122-72, 122-73 and do some experimenting. I’d start with 66 in the front and 72 in the rear for a 307. For time sake, I’d recommend that you buy the Holley Jet Kit (36-181, $53 from Summit). It contains two each from 64 – 99. You’ll never use the bigger ones – but by the time you futz around with a bunch of individual jets, it’s easy to surpass the cost of the kit. Price them local as well – there’s got to be several shops in Bellingham that carry Holley parts.

Hope this helps!
Glenn