Re: [AMC-List] backfire through carb

[Tom Jennings <tomj@xxxxxxx>]

On Tue, 2006-06-27 at 08:21 -0700, Jim Blair wrote:
> A: If you are running a Carter BBD with feedback carb, the timing will self 
> adjust as long as the knock sensor functions unless it's had the Nutter 
> Bypass done.

No, Weber 32/36 DGEV. (32mm primary, 36mm secondary) on water-cooled
manifold. Duraspark II ignition. I took the top off the carb, looking
for gasket bits etc, it's clean, jets not plugged, etc. 

Retiming it lessened the problem, but it still backfires at speed and
heavy load and low vacuum. (Local road testing vs. my 45 mile, 70mph
commute).

I have one of those timing lights with the knob to offset advance; I
used it to measure mechanical vs. vacuum advance.

I have about 15 degrees mechanical advance, about 30 deg. vacuum advance
(talking very round numbers here) 45 total. I was not trying for
precision, just go/nogo checks, so it could be 5 degrees error each.
With 8 degrees static timing that seems like a lot of total advance.

With these settings and 87 octane gas it never, ever pings, so I'll bump
timing up a few degrees at a time and get it to ping, then measure
carefully this time.

I too tune by ear; but a motor ought to run approximately right at the
factory settings.



> 
> From: Tom Jennings <tomj@xxxxxxx>
> Subject: Re: [AMC-List] backfire through carb
> To: amc-list@xxxxxxxxxxxx
> Message-ID: <1151307945.28671.64.camel@xxxxxxxxxxxxx>
> Content-Type: text/plain
> 
> Timing.
> 
> Retarded.
> 
> Me I mean.
> 
> On the road trip to Santa Fe last week I'd retarded it on the
> side-of-the-road "a few degrees" to deal with the crap gas I was
> buying.
> A "few" turned out to be 10. Can't beat actual measurement!
> Didn't
> pinging though, uhuh.
> 
> The 87-93 Clymer's Jeep 258 book I have, says the carburetted
> motor
> wants 9 - 11 btdc static timing. I never bothered to look in the
> newer
> books before [but wanted to double-check the new-fangled timing
> mark
> setup], I assumed (ahem) it would be the same as older models
> (usually 4
> - 6btdc). Wrong again.
> 
> I set it to 8btdc. I'll find out tomorrow on the drive to Irvine
> (45 mi.
> each way). I hope I'm not wrong a third time.
> 
> 
> 
> -
> 
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