I have spent the last couple of weeks tinkering with my 360 trying to get rid of what I can best describe as a fuel distribution issue...

This started out trying to ensure my engine was timed and tuned properly as it has always run warm - hot since rebuilding it a 5 years ago. I typically don't it drive much in the summer so it hasn't been to bad of an issue, but we moved to Atlanta 6 months ago, and the additional time in traffic or just the generally warmer area has prevented me from getting to drive it much. I don't want to get into the whole electric fan vs. mechanical fan debate here, just trying to get some guidance on the fuel issue. My jeeps specs...

AMC 360 from 1980 Wagoneer
Bored 0.040 over
Edelbrock performer intake / performer plus cam / performer springs and retainers / performer link timing
stock pushrods / rockers
Bulltear HEI distributor & gears
Holley Truck Avenger 670
HVH Intake spacer SS4150-1 (think this is the right model http://www.highvelocityheads.com/supersucker.html)
NKG 7131 (BPR6ES - Champion RN10YC equivalent temperature range .. http://www.championsparkplugs.com/le...nversion-chart)
High flow water pump w/ 180* high flow thermostat (Robert Shaw)

Carb Tuning...
Rebuild yesterday to eliminate leak within carb as a issue)
Stock 68H main jets / 89H secondary jets
7.5" power valve
Idle screws @ 5/8 turn out from seated (yielding 17" @750 rpm)

Timing...
Initial 8*
Mech advance - 17* @ 3000
Vacumm advance - currently on ported vacuum (have tried both, left on ported to have less advance @ idle, on manifold i have +17* @ idle)

So to my issue... Generally speaking, the front 4 plugs seem to indicate that these cylinders are running lean and the back 4 plugs seem to indicate the cylinders are running rich...



8 - Heavy Soot
7 - Light Soot (hard to see in pic)
6 - Medium Soot
5 - Heavy Soot

4 - Very clean
3 - Very clean
2 - Tan ceramic body
1 - Very clean


Its hard to tell in the pics, but the clean plugs are a bright white, like new ceramic.

I tried....
  • Increasing the jet size (68 -> 80 in small increments) ... No improvement, all cylinders richened up evenly
  • Ported, Manifold, & no vacuum advance . no improvement
  • Swap the PCV from the front port to the rear ... No improvement
  • I started with Champion RN14YC plugs, dropped two heat ranges to NKG BPR6ES ... No improvement
  • Looking for vacuum leaks ... None found, port caps replaced, hoses replaced, new gaskets after carb rebuild, sprayed carb cleaner ... nothin


The engine runs 190~200 on a cool day until i get it under heavy load and i believe it starts to detonate. After detonation, temps raise to ~220 and detonation gets worse and the issue compounds itself.

My thought is that the front 4 cylinders running very rich could lead to too much heat and detonation under load... Thoughts? Advice? Ever seen this before?