Morris man. you are right

the-lada-dude, Oct 4, 6:14pm
the vaccum take off for distibutors with this control option is placed as you said just above the thottle butterfly and see's almost no vaccum at idle. most engines are set at5 - 7 deg btdc static ig timing. if the dist saw max vac at idle it would pull another 10 +/- deg adv and you'd be struggling to get the prick started.why doesnt that ginga fella just pull the frigging rocker cover off and check overlap against TDC
the-lada-dude, Oct 5, 8:24am
what !no bites
morrisman1, Oct 5, 8:29am
I learnt about the vacuum take off for the dizzy because I accidentally tapped a vacuum gauge into it one day my mistake! ended up driving around with it like that for a few years.
bopbargains, Oct 5, 2:52pm
If youdon'tknow thebasicthings, you should stay quite before youmake more a fool of yourselfs.
Under light load, part throttle conditions the manifold pressure is lower so volumetric efficiency is lower so the cylinder pressure is lower so the fuel mixture burns more slowly. This means you need to light the mixture sooner so you reach peak cylinder pressure at the ideal time. This is the purpose of the vacuum advance. The lower the load is the more it will advance the timing. Vacuum advance will improve gas mileage and drivability of a street driven car. A lot of guys think a vacuum advance hurts performance, this is not true. The vacuum advance is entirely independent of the mechanical advance. They are two separate systems that perform two separate functions. The mechanical adjust timing based on RPM where the vacuum adjusts timing based on load. Under high load, WOT, performance conditions there is almost no manifold vacuum so the vacuum advance does nothing. The only time the vacuum advance adds timing is at part throttle, low load conditions when there is manifold vacuum. So unless you race at half throttle a vacuum advance will have no effect on performance. It will however improve part throttle drivability so unless your car is a 100% race car I would recommend running a vacuum advance.
bellky, Oct 5, 3:00pm
vac adv is a waiste of time on my rotary - the only time it would work is on decelleration/overun, might stop some of the back-firing but that's 'bout it
morrisman1, Oct 5, 3:45pm
BopBargains, I suggest you go out and put a vac gauge on the vac line that goes to the distributor. I think you will find that it is complete unrelated to manifold pressure.

Come back when you have done this. I dont have time to spell it out for you at this time so ill leave it to you to build your understanding.

I know how manifold pressure changes in differing conditions and also know that vacuum for the dizzy is different.
morrisman1, Oct 5, 3:47pm
I just had a quick look on the net and it appears there are both systems, some use ported vacuum source and others use manifold vacuum. We are both correct and both didnt know that the other system existed and both made dicks of ourselves! haha thats life aint it!
crzyhrse, Oct 5, 4:42pm
Ported vacuum is just manifold vacuum that is switched off when the throttle is closed. A ported vacuum advance system doesn't need the vacuum disconnected and blocked when setting base timing.
sr2, Oct 5, 6:17pm
Hi guys, great thread; a refreshing change from the ???my old Holden is faster than your old Honda??? threads that appear to be the norm on this MB these days. Just a few points if I may, I??
bopbargains, Oct 6, 4:55am
# 7. I was referring to # 1
the-lada-dude, Oct 7, 11:57am
BOBBARGAINSyou'd be one f'n cheeky prick to say i don't know what i'm talk'n about !read mymessage carefully , note i said idle ! the vac tale off on older cars is between the thott b/fly and the carb venturiand sees neither vac or velocity until the the b//fly goes toward part thott . yes yes , we all understand the rest of your blurb bobby as that's pretty basic stuff , eh !
ginga4lyfe, Oct 7, 12:33pm
Wait.what!
bellky, Dec 15, 3:13am
haha, just remember the-lada-dude is a windup.