16 June 93 Just completed the most thorough diagnostic, debug and dialing ever. MIleage on SW trip dropped to 11mpg. I suspected (from long history of symptoms) that it was running rich: while I could rich out the carb, I could not lean it out, including removing the idle-bleed screw. Adjustment was broad and unresponsive. Starter solenoid engages at 60 mph. Replaced at Dick Gladden's place. Found out the "CCW" direction I had fo rthe distributor was wrong; I was retarding when I thought I was advancing. Not very helpful. Also installed a ignition coil ballast, because there was visible corona and snapping, when all wires, cap etc were verified clean and correct. Upon returning home I went through: Found the vaccuum very low: idle 15inhg, cruise 10 -- 12inhg. I recalled (incorrectly...) this being a high-vac cam. New plugs, N12Y, gapped at .034. Compression checked again. Luckily there was history, from notes in Mar91, when I had burned #4 valve due to leaky intake manifold gasket (as well as the long-persistent problem, viz, below): Mar91 June93 1 145 145 2 145 155 3 148 152 4 145 145 (Mar91 note sez 140-145) 5 150 150 6 150 155 (Mar91 conditions unknown. Jun93 engine hot, all plugs removed, cranked exactly 4 compression strokes.) Worked out LPG carb design (I think) and determined that spring tension isn't worth shit re: affect on operation. The diaphragm area is simply so high it'll override anything. Though stiffer spring will make idle, low-flow conditions more sensitive to idle bleed (lean condition). Stiff spring stetched "seemed' to have some slight effect. But mileage (according to gas gauge, hardly high resolution), never noticed. Removed timing chain cover, checked cam timing and grind against the chart (see ./camshaft.timing), was absolutely correct. Went over cam timing with dad. Found that my vac/presure gauge widly inaccurate. Found out that the el-cheapo dwell/tach was useless. Bought new timing light. R&R intake/exhaust manifold gaskets. Though found slight evidence of leakage (LPG wax on seal area) squirting carb cleaner around hand't produced smoke/rpm change, and R&R did not affect measured vaccuum. Replaced PVC and breather grommet, and installed external breather air filter (instead of snorkel hose). Removed fuel/vaccuum wipre pump; leaking oil and spraying a mess. Blocked off. Tightened/replaced all vaccuum hoses. Replaced wimpy fan with excessive fan. Always cool now (even at idle). Replaced radiator hoses. Vaccuum rock-steady at idle, occasional flicker under accelleration. A call to Crower, find out that due to 108deg lobe separation, 15inhg idle/10inhg cruise is just fine. Even 112deg would have increased vaccuum. So much for memory. Ignorign specs, I yanked distributor for max. vaccuum at idle; ended up about 25BTDC (!). Left it. It never pinged (~200 mi hiway driving) Made appt and went to Suburban LPG in Hayward (Pete and Doyle). Spent 5 hours there on diagnostic machinery. Went through absolutely *everything*. Determined engine is utterly mechanically perfect, no flaw. No amount of tuning would bring engine even close to spec; typical idle (well 900rpm) 5.00%CO, 400ppmHC, 10%CO2, 0.3%O2. Starved for oxygen, running rich. At 2000+rpm, numbers dropped to ~ 2.5, 200, 11, 0.4. Rich. At least my diagnosis was worth something. Ignotion was perfect -- though the MSD "multiple sparks" beyond hte first were not enough to fire, so that's a joke. The first was large and hot, and all cylinders ran about 9--10KV. Cylinders were amazingly consistent in spark voltage, over entire RPM and load change. Could not perform the cylinder-power (spark-short) test, because of the MSD. Also, it wouldn't measure dwell; it always read 47deg. Pete hand-set it to .016. Points were fine of course. Protracted expirimentation with PCV valves, dtermined thgat stock one is too restrictive. Installed a NAPA Echlin #2-9200. Improved idle numbers. We got to 4.20%CO, 300ppmHC, 11%CO2, .9%O2 with tweaking. Idle adjustment still dead and unresponsive. Found another CA125 mixer, installed on my throttle body. Numbers immediately dropped, and after adjustment 1.50, 100, 11, 1.1. Success! Alas -- high speed numbers (2000 -- 2500) went up to 3.50, 400, ... Upon checking diaphragms, installed my old one which turned out to be the leanest possible. This solved the problem. Operating settings required slight (10%) enrichment, compromise to get the in-gear idle acceptably smooth. Idle adjustment became very sensitive; 1/4th turn lean stumbled, etc. This never happened before. Final numbers ended up being idle 1.00, 80ppmHC, 11.5%CO2, 1.4%O2. Static timing was left at 12BTDC. It appears that though the vaccuum advance operates, ti does so at too high vaccuum, and so never really works. The breaker plate may have problems; see below. So I left after 3.5hrs on diagnostics, and a new carburetor, $206.89. Just as I reach cruise speed 50mph, the engine bucks madly at throttle-up, high-vaccuum, consistently. Drive it back. This time the car is put on the dyno. The emissions are still OK. Pete gets it to buck at 50mph. Changed the fuel filter; it had at least 2tbsp slag and crud. Pulled the dist cap, and Pete says it was already at .016 (once this buckign at throttle-up happened before; points had somehow gone nearly closed?). Readjusted to .016. Upon reassembly, on dyno, problem never came back. Car produced 60--70hp at the wheels at 65mph with throttle wide open, just before kickdown. At 50mph cruise, emissions: 0.05%CO, 57ppmHC, 11.5%Co2, 1.5%O2. Bucking never came back. Mileage, gas gauge wise, seemed much improved. I suspect the distributor was either bad, timing plate sloppy, or the dwell was off when Pete opened it up on the dyno, and adjusted it without saying so.