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« on: June 28, 2020, 12:26:12 AM »
Need some opinions on what to try next.
To begin, I think my accelerator pumps (both 50cc, yellow and brown cams) and nozzles (both 40’s) are sized right. When I quickly smash the throttle 1/2 way and all the way my AFR stays at about 13 to 1.
At WOT my AFR is a bit rich at 12.2 to 1. I’m not concerned about correcting this until I get my tip in problem resolved (see below).
Details about the carb:
780 double pumper
73 primary, 78 secondary jets
4.5 power valve. But I’ve also tried 5.5 and 6.5 with similar results.
PVCR’s drilled to .0625”
10” vacuum at idle, transition slots are not uncovered. Idle = 1000rpm
Burning non-ethanol premium fuel
Float levels are set to mid window. I started with level at bottom of the window and raising it midway did help a bit.
Motor details:
10:1 compression.
Iron 427 SOHC 4V (500ish Horsepower)
Close to stock 1967 NOS cam specs. (Crane says operating range is 2500-7000 rpm)
2800 lbs street car
Here’s my problem:
The engine goes lean (16-17 to 1) when slowly increasing RPM at about 1/4 throttle and doesn’t richen up until I quickly press into the secondaries. If I try to slowly increase throttle beyond 1/4 throttle the lean condition causes snapping and popping (bad noises).
Anything less than 1/4 throttle (cruising) is a bit too rich (12-13 to 1).
When I go WOT I’m a bit too rich (12.2 to 1) I can easily fix this but I think I need to focus on the 1/4 throttle “too lean” issue first.
My first inclination is to increase primary jets and decrease secondary jets. If I do this I’ll end up with close to the same size jets at all 4 corners with a power valve on the primary side only. Does this sound normal?
Should I be looking at increasing or decreasing emulsion jets?