pertronix ignition gaps

[Anonymous]

What I don't understand is why everything says to set the advance with the vacuum plugged because as soon as I plug in it runs crappy. Why not set it with the highest initial with it plugged in?

don

 

[Lazy JW]

Okefenokee,
Are you running manifold vacuum? If so, your setup may need to be hooked up to ported vacuum on the carb. The reason for disconnecting the vacuum advance during the timing procedure is to eliminate the vacuum as a variable. That way you can tell where the initial (or so-called 'static') advance is set. Then the centrifugal advance does its thing as the engine speeds up, and the vacuum advance comes on or off as the vacuum signal changes with load and throttle position. Perhaps the advance curve for your particular combination needs tweaking?
Joe

 

[CobraSix]

Same thing as Joe said...it happened to me earlier this summer.

It drove me up the wall. I would set initial timing, and I never plugged my vacuum or checked my under load timing (3000 RPM). I would always get backfires about every 10-15 minutes. But everytime I checked my timing, it was dead on. Come to find out my vacuum advance was pulling it to the right setting at initial. I didin't figure it out until I checked my timing at 3000 RPM. Guess what it was...15* BTDC, my initial was 10 *BTDC. Problem was I over compensated the throttle and stuff which somehow opened the ported vacuum (RPMs at idle were only 700 RPM). So...from now on I always pull the vacuum to make sure.

Slade

 

[Anonymous]

OK, so if the vacuum is coming from the correct port, and mine is( the 2300 only has the one), and there should be no vacuum from this port at idle then what is the point in plugging it? If there is vacuum at idle from this port, why?

I too have been running without the vacuum advance. I am running 16 degrees initial, all in at 36 degrees. No pinging, the engine is very reponsive, if I hook the vacuum up it idles rough and loses some of that responsiveness.

I would like to have both performance and economy.

don

 

[Lazy JW]

Okefenokee,
Check to see if there is any vacuum at that port on the carb. If there is, and you already have 16 degrees advance, it will pull in a whole bunch more timing, causing the rough idle, etc. With a true ported vacuum, I don't bother plugging the port, that's just a generic procedure left over from the old days when some engines used manifold vacuum, and it ensures that you are indeed checking only initial advance.
Joe

 

[Anonymous]

I'm going to try setting it with it hooked up just to see how it does.

tks
don

 

[MustangSix]

The point in plugging into a ported vacuum is to delay the vacuum until the throttle is off idle.

At idle, most engines need little advance but they generate high manifold vacuum. The engine is turning slowly and lighting the fire too soon could cause it to run roughly or require improper idle or mixture settings. So you want to delay the vacuum until you are moving and the throttle is opened. The ported vacuum opening is placed so that the throttle covers it up when you are at idle and it cannot "see" the manifold vacuum under the blade.

When you tip into the gas, the port is uncovered and the port starts seeing manifold vacuum under the throttle blade. The distributor can start reacting to engine loads.