Racing Fuel Systems

This is a QFT 600 cfm vacuum secondary. The problem is poor transition from idle. When you first apply throttle, the engine shutters from leanness to the point of being undrivable. It has an .031 pir down low, and an .070 piab. I compared measured transition slots on a Holley 1850 [ .023] width QFT [ .027]. The height on the QFT was also taller. It doesn't seem like much, but it is about 17%. Looking for suggestions. I did try an .063 piab but it seemed fat.

I'm assuming this is SL-600-VS ( Slayer ) in it's original set up.
Are the secondary throttle blades closed to aproximately 1/4 turn past contact. If not , try that.
The larger transition slot won't cause an off idle stumble. Although an over exposed primary transition slot will.

I will try that suggestion as it worked once before. The primary trans slot with closed throttle is a little more than square. Not by much, so maybe that's why I missed it. Good suggestion. Thats why this forum is so good. Sometimes you can't see the forest for the trees.

A large/long T slot can cause an off idle stumble. The section above the blades acts like an air leak, leaning the mixture. If the slot is longer, more air gets in.

Rgalajda I closed the P throttle blade to less than a square T slot opening and opened the S blade slightly so it idles at 800rpm in neutral and 600 rpm in drive. I have an .063 IAB and an .031 IFR with 66 main jets. Warm it up, adjust idle and take for a ride. Quite a bit better but still spikes to 20 to 1 AFR. I can go to the next drill size smaller IAB or go to a .033 IFR. It will drive thru with less throttle opening but is not a drivable carb. right now.

All the QF/Proform carbs or any using that baseplate will suffer. The slots are all too large, the bandaid is to use a t-slot restriction in the body. .082 will usually be close, even then I still can feel the difference on a running engine between one with a large lot and one properly sized. Most Holley baseplates are good, BLP as well. You can play with primary exposure, too much and you get too much fuel, too little and too much air bleeds in and you get a hesitation on light or quick throttle openings. With the big slot even with a t-slot restriction it will be very sensitive.