I've been chasing this problem for many weeks now and have probably replaced 90% the ignition-related components under the hood. The problem manifests itself as a near-impossible start after the Jeep has sat in my work parking lot all day. While I am anxious to leave at the end of a long day, the old Jeep seems to want to stay. Sweet talk and negotiation have also not carried the day with the old bucket of bolts -- so here I am.
I've cleaned, rebuilt and adjusted the carb to factory spec 3-4 times now. And I'm not just talking float height. I check all those little freaky measurements they suggest and make sure all linkages are bent to spec. The rotor and distr cap are new. The fuel pump is new. The fuel filter is new. The fuel lines are insulated and held away from the block and exhaust manifold. The plugs are new. The plug wires are new. The ignition coil resistances are to factory spec (though it may be the next thing I replace). The compression is good and the timing is per the spec on my hood underside (and check with the hose plugged and the vacuum switch wire assembly unplugged).
Sometimes it goes for days before reappearing (usually right before I have an important meeting across campus I have to be at in 5 minutes). Yes, it's not just at the end of the day, sometimes at 10:30, sometimes at noon.
The choke was out of whack, despite having the correct color key. I took it to 2 notches lean and it seems to be closed at the correct times (when it's cold). Nonetheless, I find that I have more luck if I jam a small piece of rubber hose to hold it all the way open before I start it. Faithful readers, please realize that I now whip out the chunk of hose like it's some sort of magical talisman that will summon the spirit of the Jeep back to life. The spell doesn't always work, however, and I get to gaze, confused and forlorn, across the freshly-waxed hood and wonder where it all went so wrong. Is there a special form of Jeep karma that I am failing at. I let it get muddy sometimes, I even intentionally dash through an innocent mudpuddle, I always drive it with the top down on nice days. Sometimes I even take my shirt off too, to share the glory of an exceptional day. But the good times are forgotten so quickly when I'm in my nice work clothes bent under the hood while my co-workers strut over to their mercedes and BMW's and SUV's. I pride myself on being a pretty good mechanic, but this makes me feel like an idiot.
I'm sure I'm going to get a few helpful posts suggesting the old siphon effect on the fuel bowl, but I've checked that. Even before I crank the puppy, I take the air cleaner off and goose the throttle only to see the two nicest little streams of petro jet down the throat of my carby. I can do that a number of times before I see any sign of diminished fuel supply. My extended battle with this problem has left me thinking that it's more of an issue of flooding than being lean. The small rubber hose gripped hopefully, desperately, in my hand most days after work backs me up on this. Plus the odor of gas is quite strong during my cranking, cranking, cranking -- oh the dreadful cranking. I am constantly amazed at how good my battery is that it lets me crank that 6-banger so many times. I'm sure my workmates are equally impressed at how many days I can put myself through the torture of it all.
A bit more history on it: it started with troubled morning starts, but now is pretty much exclusive to warm-weather starts (sitting in the sun at greater than 75 deg F). I wonder if maybe I fixed the original problem and have been creating a succession of problems with each new attempt at ultimate correction. My current theory is that perhaps the fuel bowl float is a bit too high, allowing the gas in the bowl to slowly leak down the intake throat whilst it is warmed in the sun. There would be residual fuel pressure in the line that would refill the bowl a few times as the float opened and closed the valve, I think. I am going to drop the float an 1/8" or so, but wanted to get some time on the most recent change (new plugs, again) before I changed something else.
Please share you thoughts, or make an offer.
Bob Versluys Florence, SC '88 Wrangler Sport Soft-top gray/red "Sadie"