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Distributor Advance

F

fasterthanu

Guest
Here is a real stupid question guys. My car at 1000rpms is at 20 degrees advance. Now heres the funny thing... Keep the timing gun on it, and hit the throttle, and it retards itself!!!!!! I went down to like 12, if not lower. I did notice when we had the distributor out that the bushings in the centrifigul advance were shot, and the new spring kit I got the arms were backwards, and wouldn't fit. Would this cause the car to retard itself? Its funny, put a new set of Pro Line heads on, had them opened up, have a cam with .488 lift in there that starts to go at 3500rpm, and bought two brand new edelbrock 1405s for my dual quad set up... She feels sooo much stronger, and at 4000rpm really wants to run. Yet, with the old smogger heads, and piece of junk carbs, I ran 0-60 in .5 faster. And still, if I use my stall speed and brake torque to 2600 rpm, I still amd .4 slower in 0-60 compared to me hitting the gas and going. I am sure that this problem has to do with my advance.. Am I right?
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
From a constant rpm (like the 1000 you mention), when you jerk the throttle open, you SHOULD show a momentary loss of advance, as the vacuum advance just disappeared as the manifold vacuum dropped when you opened the throttle. However, your centrifugal advance should come right in as rpm increases, so you'd only see the timing retard for an instant.

You can check the operation of your centrifugal advance by disconnecting and plugging your vacuum advance line (like you do when you set your initial timing) and noting your base timing; then gradually increase rpm to the point where the timing STOPS advancing (usually around 3500 rpm or so), and note that point. The difference between the two is the amount of advance the centrifugal system is providing. This is much easier if you have a dial-back timing light, as you don't have to add marks to the balancer or add a timing tape.
 

Jack

Well-known member
Joined
Dec 27, 2000
Messages
1,825
Location
Florence, SC (Timmonsville SC)
Corvette
71 War Bonnet Yellow VERT 71 BH Blue CPE (SOLD)
JohnZ nailed it! Follow his assessent & instruction. AFTER ... you get the basics adjusted ... THEN ... you might experiment with when your total advance is all the way in. Varies with cam, comp ratio, stall, gear ratio etc ... yours might optimize if timing was all in by 3200 or 3000 or 2800 ... even earlier. Then again, 3500 may be right for your combo ... dunno ... experiment w/ springs & adjustable vac can AFTER you've got the basic adjustments correct.
JACK:gap
 
F

fasterthanu

Guest
my advance stays down while increase of throttle. Didn't have rpm gauge next to me, or anyone in the car, but it DID go and stay down as I went up in rpm. =( I was at about 2500rpm-3000rpm, and timing was at 10degrees =(
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
Sounds like the centrifugal advance cam, weights, springs and stop bushings "need some work" to put it back the way it's supposed to be so it works, and gives you the curve you want. If you don't have distributor experience and a dial-back timing light, I'd suggest you take it to a shop that has a Sun distributor machine and have them rebuild and re-curve it for you.
 

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