You will truly know if the IFR’s are too big when you fit an AFR gauge and monitor fuel delivery through the t-slots. Right now at idle your regulating fuel through the needle point and seat that make up the idle screws. How much the exposed t-slot is pulling plus other factors such as mentioned varied manifold flow and egr have an effect on idle screw position. See pic below for where fuel travels before you regulate it with idle screw.PRNDL wrote: ↑Fri Dec 09, 2022 11:31 am Thank you guys. It’s 90% better now. You have been a big help. The stumble is even gone. Radiator is done. I did it last night. Need to do my plugs, oil, and filter. I’ll report back.
I’m going to leave my IFR’s alone due to my mixture screws being around one turn out. I figured if the IFR’s were too big, I would be at 1/2 turn or something.
- BLACK = Mainwell
- BLUE = Idle/transition fuel path
- GREEN = Idle fuel regulated by idle screw
- WHITE = Upper IFR position
- YELLOW = Lower IFR position
- ORANGE = Fuel to t-slot (baseplate)
- RED = Fuel to Idle discharge hole (baseplate)
- Purple = PVCR
* upper IFR needs to lift float level fuel in order to meter and so needs to be larger and potentially less stable delivery. Lower IFR has float level head pressure to feed it and therefore can be smaller diameter to meter and more stable delivery. Lower can make for easier engine starting too as there is a column of fuel to float level after the IFR to give a little rich unmetered slug of fuel to help first fire.