>>> "Tom Reichard" <tom@lakemurray.com> 12/09/97 08:48am >>>
>My recently-acquired '77 Midget has a backfiring problem when the
>accelerator is released suddenly and the engine is winding down (is
>"overrunning" the correct term?)
Before I yanked the motor out of my '74 B, I had a devil of a time
keeping all of the exhaust bits from leaking. This caused my car to
have exactly the symptom yours does. The biggest problem I had was the
connection from the manifold to the exhaust pipe. Between sealing rings
that disintegrated and nuts that would loosen up I spent a lot of time
under the left front wheel. In your shoes, I'd check for exhaust leaks
first.
As to setting the mixture: Don't. It's probably just fine.
If you just can't keep your hands off the thing: Get it warmed up and
idling. Connect a vacuum guage and tachometer. Twist the idle mixture
screw a quarter turn at a time and get the highest vacuum reading you
can. (If you lose vacuum, you're going the wrong way.) When the idle
gets a little too high or low, set it back to spec and continue with the
vacuum guage. At a point, turning the mixture screw in the direction
you're going won't make a change anymore. Turn the screw IN as far as
you can without losing the very best vacuum you can get. Did that make
sense? In other words, turn the screw IN until the vacuum just starts
to drop off, then turn it back out to get back to the best vacuum
reading. (Turning the screw in leans the mixture. Turning it out
enriches it. This is pretty standard for any downdraft carb. An SU is
opposite.)
They say with the dual SU's, goose the throttle every few minutes to
dissipate the puddle of un-aspirated gas in the manifold. That puddle
will throw off your adjustments. If your weber is a downdraft, this may
not apply, but it won't hurt.
As for the "rank newbie" questions, don't apologize. For some of us,
it's all we can answer, and it makes us feel like we're contributing.
Matt Kulka
'74 B - Not backfiring now, but that cat...
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