1978vett

Can someone tell me exactly where on the carb the vac advance should be connected on a 78 L82 Auto trans Thanks

doorgunner

Exactly? No. But it should be connected to a port that has NO vacuum while idling......

and.....as the engine rpm increases-----the vacuum at the port increases.

speedreed8

look at designation 'A' in the diagram. front ,throttle side on qjet
http://willcoxcorvette.com/instructi..._hoses_l82.jpg

doorgunner

Thanks for bailing me out !

1978vett

Thanks for the info..

7T1vette

What fitting you WANT the vacuum line connected to might be different than where GM put it at the factory. In '69 or '70, the line going to the vacuum advance canister came from a "timed" or "ported" vacuum fitting. The concept was that at idle, the engine should be retarded so that it created less polutants...even though it wasn't best for the engine and caused it to run hotter.

So, if you are a really 'green' person, leave it connected to a "timed" fitting. However, if you want a better quality idle that is also better for the life of the engine, connect it to a "manifold" vacuum line.

If you have yearly emissions testing requirements in your state, you may want to put it on a timed fitting for doing the emissions test, then move it over to a manifold fitting for normal driving.

1977L48

i know this might be off topic but how does less timing make your engine run hotter? i was always under the impression that less timing translated to running cooler

doorgunner

The concept was that at idle, the engine should be retarded so that it created less polutants...even though it wasn't best for the engine and caused it to run hotter.


Good to know!

Rookie answer about running hot: If the timing is set very high----then lessening the timing can help it idle at a cooler temp

If the timing is too low---the engine temp will increase.

7T1vette

Retarding the timing at idle (by artificially blocking off the vacuum advance signal) makes the engine run hotter. And a hotter combustion chamber results in less pollutants. At least, that was the concept.

But the idle quality was poor and the emissions system had to include a 'failsafe' system in case the engine ran TOO hot; so there was a HI temp switch that cancelled out the vacuum advance 'defeat' system. If the car idled too long and reached excessive temps, the vacuum advance was restored until the temp dropped to normal values.

doorgunner

Man! GM solved problems.....

but created more problems....

then solved the created problems.....

leaving intermittent problems....

which solved each other........temporarily.


I think I've got it now!

7T1vette

GM designed a good, simple engine. The EPA then stipulated additional requirements with which GM had to comply. That's where the system complexity unfolded.

1978vett

I see

doorgunner

Good point!

(Makes me think that the EPA was in charge of the Viet Nam War )