Likely the 6.5 was leaking and the 3.5 was not. A properly functioning power valve will not effect the idle circuit. I can show you guys more on this when we put my GTS on the chassis dyno. Just need to find an 850 dp to test with first.
I have an 850 DP with anular boosters that I can send you for a test mule.
If you like it but it and if not just send it back . I have some QF billet metering blocks and quick change float bowls on it but will send all the stock stuff as well.
Worst that could happen is you Dyno t me a carb for me ...lol
Would love to see the results !