Edit: Updated post, see below. Problem seems to be fixed.
This post is long, but I am trying to get all the info out there that might help with the diagnosis. I already know I am going to rebuild the carb, but I don't have much experience with Holley carbs. This is a
Holley Street avenger #80670, about ~600cfm or so. Are there any problems/pattern failures to watch out for when rebuilding one of these carbs?
More info below to hopefully help you help me.
I am experiencing what I suspect is a lean backfire on my 77 Cherk w/360. The problem popped up a few weeks ago, I get intake backfires under moderate load, any speed above 35 or so. Level cruising, it seems ok, but add throttle for a slight hill or grade and it begins to slightly surge. Add more throttle, it will backfire multiple times. NOTE: This isn't an accelerator pump problem, the jeep is fine off the line. A visual check shows plenty of squirt from the pump.
At first I thought it was ignition (HEI conversion) so I replaced the cap, rotor, ignition coil and plugs with new.(Napa parts- Echlin and Autolite) Old cap was worn, rotor was in ok condition. The jeep ran better, not a big improvement, but I could feel an improvement. Note: Module was replaced a few months ago, Echlin brand.
Old plugs were in good shape, but showed lean. I had reduced the jet size in a quest for better MPG, so I reinstalled the jets that it came with. (#65, stock for that carb #, didn't touch the secondary jets, primary only) No noticeable improvement.
Other info: Float level checked and correct, float bowl clean, new fuel filter (with return, oriented properly
) Timing is 10*BTDC, Ported vacuum to advance (runs the same with manifold vac) Power Balance test with Snap on Scope shows all cylinder firing evenly, KV readings range from10-12 kv. New MSD wires installed and removed (misfire at idle with wires) Fuel pump volume and psi checked, in specs. (Pump was replaced about a year ago) Fuel lines are new, tank is very clean internally.
Engine runs smooth at idle and low rpm, starts right up every time, hot or cold.
So, any thing I missed? Suggestions? What should I watch out for when rebuilding the carb?
Thanks
Curly
I start what I finish.
81 Wagoneer 4.2/auto
77 Cherokee S 360/Auto/QT
97 Jeep Wrangler