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Running without Vac. advance

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Dennis P

Jedi Hopeful
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Hello, My HS4s faded out on me, so I put in a pair of HIFs, I had redone in the winter.
What a wonderful difference. Car has better acceleration and power. But, I forgot to connect Vacuum advance at intake manifold. Old carbs had pickup at rear carb. HIFs use manifold, having no pport, I never did it. Runs lke a beast. should I leave it alone?
 
if it ain't broke don't fix it
angel.gif
 
i,ve driven my Rover 2000TC for the last 2 summers without vacuum advance....Has ran great.........Heed the other post..........If it ain,t broke don,t fix it

Bill Robertson
 
My vacuum diaphram broke 20 years ago. Haven't missed it a bit.
Bob
 
Leave it disconnected...it isn't a problem.
Vacuum advance is one of things Brit-car racers tend to eliminate. It can help a bit with low end torque, especially if you chug around in high-gear, low-RPM situations. For those who drive in a more sporting manner, the vacuum advance has little or no effect.
On the Lucas 25D distributor in my Spridget, the entire advance unit has been removed and the hole has been plugged. The moveable points plate (connected to the vacuum unit) is safety-wired in a fixed position.
 
Well, the news is good. When I took my 72 Cutlass to a specialty shop, a few years ago, the first thing they did was disconnect the vacuum advance and the car ran great. Good to know the same applies here. Thanks for the help, Dennis
 
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Webb Sledge:
what's vacuum advance?<hr></blockquote>

Hey Webb -

As the needs of the engine change due to acceleration, load, etc., the timing of the firing of the spark plugs changes. In order to do that, the position of the rotor inside the distributor cap with respect to the poles on the cap, which conduct the electricity through the plug wires to the plugs also changes. So the plate on which the points is mounted has to shift. A vacuum advance unit uses the suction from the vacuum produced naturally by the engine to "pull" the plate back and forth to change positions.

Mickey
 
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Dennis P:
But, I forgot to connect Vacuum advance at intake manifold. Old carbs had pickup at rear carb. HIFs use manifold, having no pport, I never did it. Runs lke a beast. should I leave it alone?<hr></blockquote>
Vacuum advance improves gas milage during part throttle cruise conditions. On street cars with anemic engines There isn't much part throttle cruise since they have to be pushed fairly hard to maintain highway cruising speeds. You are not likely to notice any improvement with vacuum advance.
D
 
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Mickey Richaud:


Hey Webb -

As the needs of the engine change due to acceleration, load, etc., the timing of the firing of the spark plugs changes. In order to do that, the position of the rotor inside the distributor cap with respect to the poles on the cap, which conduct the electricity through the plug wires to the plugs also changes. So the plate on which the points is mounted has to shift. A vacuum advance unit uses the suction from the vacuum produced naturally by the engine to "pull" the plate back and forth to change positions.

Mickey<hr></blockquote>

That's all true, Mickey, but you forgot that the mechanical advance also moves the rotor position on the shaft to do the same thing. The problem with most standard timing curves built into the mech advance is that it doesn't get to full advance until a very high RPM.
This is compensated for by installing weaker springs on this part of the distributor which causes the full advance to come in at a lower RPM. This gives more mid range power and flexability to where you don't need the Vacuum advance.
Mine has a '75 distributor which happened to be set up that way stock and I have no problems with bogging down that someone else mentioned and I can easily start off in second and come down in the low twenty MPH range in high and still get off OK without downshifting.
It also will give more acceleration power because the vacuum goes to nothing anyway under accerlation in the lower RPM ranges and the mechanical advance coming in earlier will get rid of that bogging down and will out accelerate a car with standard mech advance curve.
Here is a web site that is excellent in tuning the Lucas distributor. https://www.telusplanet.net/~chichm/tech/lucastuning.pdf
Bob

[ 05-12-2004: Message edited by: mrbassman ]</p>
 
You don't have a probelm, as there is no vacuum port, but in general, if a vacuum port is not used, it should be plugged; otherwise it will act as a vacuum leak. You will not be able to adjust the idle properly, and the car may run too lean at idle.
 
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by FWK-MGTF:
You don't have a probelm, as there is no vacuum port, but in general, if a vacuum port is not used, it should be plugged; otherwise it will act as a vacuum leak. You will not be able to adjust the idle properly, and the car may run too lean at idle.<hr></blockquote>

Yes, definitely. I left a short piece of vacuum hose on my port and put a screw in it.
Bob
 
early ones work opposite....mech advance only early, vacuum advance at 1800-up
 
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