Re: [AMC-List] backfire through carb

[Tom Jennings <tomj@xxxxxxx>]

No suggestions on the backfire? I think I'm wrong on it being through
the carb, it just "sounds like it" while driving. I'll pull the air
filter (annoyin Weber clips) this weekend to make sure it's not in the
carb. Could be I suppose.

If it were through-carb backfire, on WOT/2000rpm, that would only be too
much advance, right? So it would be firing before the intake fully
closes? 

Through more test driving I realized it backfires a lot of the time,
always wide open throttle under relatively low-speed, high-load
conditions.

I'll re-check timing this weekend, but I know the total was 40 or so,
and that mech and vacc advances were at least working.



On Mon, 2006-06-19 at 20:34 -0700, Tom Jennings wrote:
> 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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