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Re: "hanging" revs...

To: "Paul M." <rowman22001@yahoo.com>
Subject: Re: "hanging" revs...
From: "Jeff Fayne" <fayne@attglobal.net>
Date: Wed, 7 May 2003 16:35:49 -0500
> If I'm at idle, and I blip the throttle, the engine
> responds quickly and revs freely, but when I lift off
> the pedal, the revs kinda "hang" up there and come
> back down to idle somewhat slowly.  Not REAL slowly,
> but just a little slowly...  Is this a function of the
> air pump or something?

I'll assume you cehcked the obvious binding of the throttel cable...

Sounds like you're experiencing the effects of the poppet valve on the carb
throttle plates. The plate is fitted with a spring loaded valve, which opens
when the throttle is closed quickly. The idea was to reduce emissions, by
leaning what would normally be an over-enrichening during this high vacuum
period. The by-product of this leaning is that the engine does not want to
return to idle quickly.

The cure is to either:

Solder the valve closed (risky as you may warp the plates)
-or-
Purchase plates without the valves (side benefit is that you get a tad more
airflow without the bulky spring blocking the throat.) Be sure to get new
screws and peen them over.  An recent posting explained how to correctly
center the plates in the bore.

Let us know what you find...

Jeff
'70B

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