[AMC-List] backfire through carb

[Tom Jennings <tomj@xxxxxxx>]

I just (Sat.) got back from a trip to Santa Fe (RT from Los Angeles).
Car ran great, got 20mpg, rarely drove under 70 (rarely over 75). About
2000 miles in a week. Half way, had to retard the spark about 3 degrees
to take the cheap indian res 86-octane gas.

But today, though otherwise running good, I have a nasty backfire, at
low car speed/wide-open-throttle, typical "bog" territory; take off from
a traffic light up a mild hill, heavy load, WOT at about 1600 rpm (auto
trans), lots of backfire. Back off throttle, accellerates fine; WOT,
backfires. Once RPM is up, it doesn't.

Carb is a Weber 32/36DGEV on a 258; 904 auto trans, 2.73 axle, stock
tires.

What causes backfire under this condition? I'd think timing, except that
I just adjusted it very closely, checked vacuum and mechanical advance.
Since I did the road adjustment I can't tell you precisely what static
is; I had it about 7btdc static, it's probably no about 4btdc.

Could it be not enough accell pump squirt? The pump lever on this carb
had a deep groove from wear (I bought it used). I filed it all flat and
readjusted, but the pump diaphragm could be leaking (again).

(I also have a high rpm burble, wide open throttle also, say 3400+ rpm
at 70 mph, that I think is from leaning out, either jetting or
inadequate fuel pump. It's not strictly RPM, but total fuel demand high
speed and WOT.)
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