I know my cam is a little big even though I got the smallest Thumper. I have it idle at 800 rpm, the accelerator pump is fine, I run ported vacuum advance. My plugs are hard to read, timing looks good, heat range seems fine, porcelain looks okay.
I want to fix this and have thrown multiple set-ups, springs, carb cleanouts and my thinking is there’s no way I should be running this rich. I am thinking it has something to do with engine vacuum because Thumpers are known to have lower vacuum and therefore I’m thinking the signal to the carb is making the secondaries open too fast. I’ve even leaned the secondary jets to a. Using my Edelbrock Tuning manual, I’ve gone to the #10 setting on the model 1406 Calibration reference chart which is 2 stages leaner. It only improves slightly as air conditions improve, but not much. My problem is my AFR gauge goes fat (and the Jeep feels fat as soon as I dip my toe into the main jets, and wide-open throttle (WOT) never goes leaner than 10.5:1 to 11.5:1.
It also has Edelbrock headers and a wideband AFR gauge with dual exhaust and Flowmaster mufflers. The ignition is MSD set at 14 degrees initial with 36 degrees total. The intake is an Edelbrock Performer with an Edelbrock 1406 600 cfm carb.
The engine is an AMC 360 rebuilt with 8.75:1 compression, stock heads, and a COMP Thumper cam with 226/241 at 0.050-inch tappet lift with 0.491/0.476-inch lift and a 107 degree lobe separation angle (LSA). I have a 1972 Jeep CJ-5 with a 3.73:1 gear and 33-inch M/T tires. Just loosen the small cover screw, move it aside, and the primary metering rod and spring are easily accessed for metering changes. The nice thing about tuning Edelbrock carbs on the primary side is that minor changes area easily accomplished.