Drew - I actually agree with you that a .035 IFR is a monster, and in general, I don't love QFT after talking to the guys there, but lots of guys, including Brent have great luck. The issue I have with an IFR change is too many changes at once. Cam timing, PV, likely too much accel pump. More than that, don't worry about us arguing, you and RJP are the two guys I can really talk carbs with, happy to have different opinions. Just trying to slow the train down a bit on this repair.
Paul - The thing about an IFR is that the "idle" term can be misleading. The IFR feeds two circuits, idle and transition.
The idle circuit gets fuel from the IFR and air from the IAB and makes an emuslified (bubbly) mix that can easily fed to the motor. The amount of that mix is controlled by the idle screws, so, you can control idle a/f by the idle screws, even if the IFR is too big
The other circuit is the transition circuit, the vertical slots you showed us pictures of. Those provide fuel before the air starts flowing over the boosters enough to pull fuel in cleanly. Those are not adjustable, however, their reaction is controlled by the width of the slots, the amount of vacuum, the IFR size, as well as the IAB. Think of a soda straw with a hole in it. Big straw, small air hole in the side of it, suck hard, you get lots of soda pop. Small straw, big hole in the side, don't suck hard, you get little soda and lots of bubbles
You are changing how hard the engine sucks, and at the same time, going to change the overall idle a/f requirements and adjustments because of that, and verifying TDC, which could change the timing curve. (BTW, I know you say you have no reason to think it's bad, but you have to check with a piston stop, been a while fighting this engine and time to rule things out for good)
I think you "may" need to close the IFR, but because you are going to change how the engine behaves under it, I think you need to wait. The PV I'd change in a heartbeat, but if you didn't want to go inside the carb yet, that would be understandable in the "1 change at a time" logic
The big thing here is when you advance the cam, there are going to be significant changes. If I had the truck here, this is how I would attack as a first step.
1 - Advance the cam
2 - Verify TDC with a piston stop (no other way)
3 - I'd likely return the carb to QFT original delivery if it's sitting on the bench, however I'd call that optional, especially if it's still bolted on. If it wasn't on the bench, I'd likely just fire it up
4 - Set initial timing and verify the curve is correct, especially if TDC needed to be marked. If you have vac advance, hook it up after you set timing to ported vacuum, ad make sure vacuum is dead at idle.
5 - Adjust idle a/f and idle speed, somewhere around 800 for that cam
6 - Road test and gather information for next change
Now, the issue I have though is you haven't posted the list we are going to work off of, so all I am doing is pushing you to higher vacuum and a proper set up If there are other issues, then I may adjust. Better to "plan the fight, then fly the plan" right now, I think we are looking at each symptom separately, so when able, really would like to see a complete complaint list.
