Timing

I just finished my power steering project on this one, and wanted to check a few other things while I had the chance. This is the 73 with a Qjet carb. When I checked the timing, it was running around 25 deg. BTDC with the vacuum hose attached. About 12 deg with the vacuum hose plugged. For some reason, I have full manifold vacuum on the advance port all the time.
I double checked the location for the vacuum advance on this carb and it's correct. I thought vacuum advance was for under throttle situation, not idle.
What is wrong with this thing?
TIA
Its hooked up here

 

There are many arguments for this topic. Some say it was almost always manifold vacuum before pollution controls were installed and ported after. I believe the 1973 models
used a temperature controlled vacuum valve to achieve better emissions. The thoughts range to having more advance at light loads such as when idling and cruise. That is why we
we were told to plug the vacuum port when adjusting timing. With emission controls they wanted to use some un-burned fuel to get the catalytic converter hotter to reduce emissions.
When the new mandates started I saw automobiles gas mileage drop by half. It didn't make sense to me that burning twice the fuel reduced emissions. I have taken the deep dive
on the ported versus manifold vacuum and everyone has their own idea on it. Too much advance while can create hard starting issues or pinging and there a lot of information on using
a vacuum gauge to time your engine. If it pings, then retard the timing but what if you don't hear the pinging and damage your engine? Now they have knock sensors to do the retarding.
Then there is term used "my my timing is all in at pick a number", would rather it be called total advance. So you have initial, mechanical and vacuum advance. At cruise it can end up
being 45- 50 degrees BFTDC. Then there are different vacuum modules that can be fast, or slow opening and limiting.
y
So in tour case "I thought vacuum advance was for under throttle situation, not idle" if it starts well and runs good no problem. Manifold vacuum goes goes away as soon as the throttle opens
and resumes when at cruise. Ported vacuum does not come in to play until cruise. Both varying depending on throttle opening. At least you working with your and V8 and not all the oddities of
of your V6's. In the process of installing a permanent vacuum gauge and AEM wide-band sensor for my V6 and some day will make a post on my findings of what works best for me.

Long post but hope it helps. John

 

Thanks for your input.
I'm old enough to have trouble hearing, so I would probably never know if it knocked or pinged.
Just seems like a lot of advance for idling. With this situation, when would the engine ever see the non vacuum advance timing of 12 BTDC?, Except under hard throttle situation.

 

There should be a ported nipple on your quadrajet above the butterflys. It may and should have a plug/cap on it. The advance at idle comes off as soon as you
push the throttle when connected as in your picture from what I can tell. If you pull the hose off at the distributor, have vacuum on the hose and your idle changes,
then that is manifold vacuum. The only difference is manifold vacuum at idle and both react the same in normal operation. If using manifold vacuum , pull the hose at
the distributor when setting timing. Best to plug the hose either way as a habit.

My thoughts are to use manifold vacuum if possible to burn the fuel and not my eyes. Idle is a low load condition, the same as cruise. I take it that all emissions components
have been removed. With an initial timing of 12 degrees and with vacuum 25 degrees you should be good as long as it starts ok. Think of manifold and ported vacuum as a
switch. Manifold vacuum is always on and ported the switch is off. The throttle plate turns the switch on when opening and both ports sense engine vacuum.

 

You are plugged into manifold vacuum. The ported nipple is in front on the other side either above or below the fuel inlet, depending on which carb you have.

 

Thanks
I will check on that