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post #2 of (permalink) Old 05-21-2005, 10:58 AM
Way Outta Control
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Re: vacuum advance question

Nearly impossible to change the amount of vacuum from the carb. The 2100 is designed to be a strong vacuum, the stock HEI needs a weak vacuum.
But there is a simple and easy solution - match the distributor to the carb!

Get an adjustable advance diaphgram - parts stores etc. About $20. Preferably a Crane. Make sure it has a little cam like thing in the kit for limiting the total. Sometimes they get lost - some of the Chinese junk doesn't even have them.

If you don't adjust it properly your troubles will be WORSE!

Install it - the vacuum pump helps you get to the screws.

First step -- Install the limiter cam for the adjustable - it's a small piece that goes under a screw to limit total travel. Initially set it so it limits travel to about 1/3 of the total available travel. That's very important - without the limiter it can move it about 40 degrees -- waaaaaay too much.

Then through the vacuum nipple, adjust it to the LEAST SENSITIVE position -- if I remember right, that's counter clockwise - opposite of what you'd think - but look at the instruction sheet to make sure.

Do not use the mechanical weights and/or springs with it, unless you are building a street machine. You want the mechanical to come in sloooow too. Stock weights and spings work best for an off-road machine where you want low end torque. They are fine for the street too. The light springs and fast curved weights are good if you are launching at 3000 R's.

Install the distributor, time it with vac disconnected to about 8 degrees.
Connect vacuum - check to make sure the advance does not change with the line connected - vacuum should be at it's lowest point if it's the correct ported vacuum.

Check the full advance to make sure total advance is about 35 degrees at 3000. Use the limiter cam to get it in range.
Now, adjust through the nipple to get the vacuum advance so it doesn't start moving till about 1200, advances slowly and evenly to full at about 2500. You'll probably have to reset the limiter cam a couple of times.

Remember - vacuum advance readings are in addition to the mechanical, so it's best to get a "feel" for the mechanical's curve before adjusting the vacuum curve.

It takes a little trial and error, but you'll be ALL SMILES once it's dialed in!

And - a thought -- you did eliminate the resistor or resistor wire feeding the HEI - it needs full 12 volts through a heavy wire - preferably 10 Ga. It's power hungry!

Who says 258's can't turn 6000? (But don't with an unbalanced used engine.)


Let us know how it fares.
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