Re: New heads and intake, now engine bog off the line
Yeah, I played for years with my HP carb body...., then, I bought the ultra XP body and drilled out the middle of my base throttle plate - I made the hole bigger. Note: The holley base plate has air channels going from the middle hole to all 4 throttle holes on the manifold side. Then, after I turned the idle ease fully open, I could close the throttle plates more, which is the right way to solve the lean stumble. Two main things were key to me getting rid of my lean stumbles when tuning for an efficient carb (ie. not too rich settings to cover up lean stumbles).
1. Using vacuum advance at idle, so, I am idling at 22 deg. initial plus 16 deg. of vacuum advance for 38 deg. of total timing at idle. This allowed me to close my throttle blades more at idle.
2. Idle-Ease. Open all the way allowed me to close my throttle blades even more at idle.
For me, when I got my secondary throttle blades basically closed and my primary throttle blades just at the beginning of the T-slot, my lean stumbles disappeared -- even with a lean idle.
So, you can add the idle-ease to your existing double pumper by replacing your body with a ultra XP body (approx. $200). You can reuse your existing base plate, bowls, metering blocks, etc... I validated this by calling Holley. For the base plate, just make sure the hole in the middle is big enough. The old zinc holley base plates 116-112 has a big hole in the middle, but, the new holley aluminum 116-112 base throttle plate has a small hole. Both versions have air channels to route the idle-ease air to all four throttle holes. I drilled the middle hole of my new aluminum 116-112 holley throttle base to the largest size I could without hitting the air channels on the manifold side of the base. This was a good move because it gave me a lot of tun-ability with the idle-ease. In the end, I used all the idle-ease adjustment, so, I was glad I drilled out the hole in the throttle plate to the bigger size.
Here is a pic of my stock DP 116-112 base plate with the ultra XP body (hard core grey) and my QF DP metering blocks and the chrome bowls off my old DP. The carb. works great. Much better than my HP.
Note: there are no bosses for Nitrous on the Ultra HP body, so, you need the nitrous bracket that mounts to the carb stud. I had to drill and tap the second screw.
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers
Last edited by hjdca; Jul 4th, 19 at 11:53 AM.