>Ok guys...my lack of knowledge/experience with carbs is showing
again. The
>scenario: When cruising on the fwy in 4th gear (1600 with R16),
everything is
>fine and dandy. When I approach an offramp, I'll let go of the gas
and let
>the car decelerate gradually in gear. After a little while though,
there's a
>cute backfire that has the typical gun shot sound (scared the
bejeezus out of
>me the first time!). After the bang, the car still runs fine and
doesn't miss
>or show any other symptoms. So is this a major problem that I
should worry
>about, or is it just typical of a carbed car that can sometimes run
a tad
>rich?
Hey Van!
What's the deal? Thought you went hi-po with an SR20?
That backfire could be caused by a few things... FWIW, on the
240's, Nissan added an "Anti-Backfire" (aka AB) valve to hold the
throttles open a smidge on high rpm decel, so this really does fall
under the "typical" category.
What happens when you let off is that the throttle plates snap
shut - but the engine is still sucking a ton of flow - but if the
air can't flow, it'll make up for it with more gas.... the rich
mixture, when exposed to oxygen rich air OR hot exhaust, goes
kaboomie.
Heavier dashpot oil might help, also, if your exhaust is leaking,
it'll pull in cold O2 rich air, a sure recipe for backfiring. You
can try leaning the mixture out a bit, but if you overdo it, you'll
go over-lean, and that raises engine temps (more pinging, maybe more
backfiring). As always, start with a top-notch tune-up - valves,
points, timing, carbs, etc...
Sorry this is so disjointed, but it's early...
K
ps- my 2000 backfires on decel too, but more of a popcorn-popping
racecar event instead of a gunshot;-P
pps-had a '62 Pontiac with HUGE exhaust leaks, did what yours does,
'cept it exploded the muffler like it was a paper bag =8-] Talk
about scary!
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