When I turn the key off the engine seems to breathe backward through the carb.

Sounds like the noise a horse makes (not a "neigh" or a "whinny".

I don't know how else to describe it.

It just started this a few weeks ago. It does it at most any engine temperature. Did it running a 160 thermostat, a 180 thermostat, and still does it with a 195 thermostat.

With the hood up you can see it puff out of the air cleaner.

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My Web Page (http://www.landry-family.com) (updated 11-02-02)

"Long Live Freedom!"

Chad Landry
TC Member #643
ACES Member #4556
'68 El Camino

I think what you are describing is run-on or deseling. The most common cause is the primary idle screw is adjusted holding the butterflys open too much. Have you changed timing or adjusted the idle mixture screws and then had to reset the idle recently?

Another thought is the 305 in my El Camino will run-on when it hot if I use low test 87 oct gas. If I run 89 oct it shuts off fine... Have you changed the brand or grade of gas recently?

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...Dennis
The '69 (http://chevelles.com/showroom/ww.jpg), the '96 (http://www.camaroslimited.com/graphics/memcars/96ss.jpg) and The El Camino (http://chevelles.com/showroom/DjD/dsc00016.jpg)
Team Camaro (http://www.camaros.net)
Camaros Limited (http://www.camaroslimited.com)

Neither of the above. I have noticed it wants to idle a little higher (now that you mention it). So an idle adjustment might be in order.

I think you should start checking for a vacuum leak. The extra air pulled in through a leak could will cause dieseling or run-on as you described.

Thanks, it would make sense that a vacuum leak would show up like that since I didn't adjust anything.

That was it, a vacuum leak at the rear of the carb gasket. The rear carb nuts weren't tight.

Thanks for the help! http://www.chevelles.com/forum/smile.gif

Chad