Good news, Bob, the backfire was gone without the air pump connected.
Hooked it back up, and the backfire returned.
Now lets try and reason the theory out.
At 08:38 PM 4/26/98 -0700, Bob Sykes wrote:
> I think there is vacuum switch
>and an "idle detect mechanism" on the carb.
Would that be the "by-pass valve" and "temperature compensator" on the ZS
carb? The temp compensator is there to increase the idle when the car is
running hot, isn't it (it's a bimetallic strip), so that wouldn't give us a
backfire. But the bypass valve is 'sposed to hold the revs up on overrun
isn't it, like an old-fashioned carb dashpot. Hmm.
I didn't touch it during the carb rebuild except to install a new gasket.
I have also heard of some owners blanking it off when it fails (it holds
the idle at 2500 rpm then, right?).
Anybody care to comment on this line of reasoning?
>
>I can get my car to act like yours (backfiring on the over-run) by
>installing a gutted catalytic converter and using the air pump.
>If I use a "real" cat-con the car doesn't backfire. Also if I
>disconnect the air pump it doesn't backfire. I've seen the same
>thing duplicated on 3 '78 Spits and some Datsuns.
As I said, my Cat can't be totally gutted as it was glowing very red during
the carb shakeout. I'd rather not replace it as I'd like to install
headers after the car no longer has to pass smog inspection in two years.
> Could be running too lean, perhaps.
I inspected the plugs just before I disconnected the pump. They are light
brown at the electrode, maybe a little sooty on the edges. But I nudged
the mixture a little rich anyway. I can hear the difference in the idle now
(worse).
Club meeting tonite, I'm taking the Spit there and will report back.
Comments on the above thoughts are welcome.
Atwell Haines
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