Spark Advance

[Cobain03]

i just bought a new spark advance and it said that you must adjust it. i found letters on my dizzy and turned it 3 times. my question is, i hooked up a pressure gauge to it and it takes about 7lbs before it starts to move. is this good/bad? can i adjust to make it better?

 

[65fastback2+2]

dont you have electronic ignition?

 

[Cobain03]

nope

 

[brianj5600]

I have no idea what you are talking about. What spark box? What distributor? 7lbs of pressure?

 

[DJCarbine]

Vacuum advance? Takes 7 pounds of pressure to move the advance plate?
Did you buy an adjustable vacuum advance unit? What numbers on the distributor... I am so confused What did you turn 3 times...

 

[Cobain03]

ok on a distributor, you have a vaccum diaphram sticking out of the front with a outlet. you have a hose running from the carb to this for vaccum purposes.

i went to advanced auto and got one for the car. intructions inside said to turn it x number of times. look on the carb for the reference number. it said 3 times, so i stuck an allen wrench in the outlet of the diaphram and turned it three times. this adjust the amount of vaccum it takes to move the internals of the distributor.

 

[thehueypilot]

I believe to adjustment is for total advance at a certain RPM. For example my distributor is curved at 34 degress at 3000 rpm so when you rev the engine to 3 grand the total timing should be 34 degrees, but if your vacuum advance is adjusted wrong it will read either higher or lower at 3000 rpm hence the adjustable part. I adjusted my vacuum advance so that at 3000 rpm the timing was 34 degrees total with the vacuum advance hooked up. Thats how I understand it.......as it effects travel distance.

 

[Max Power]

You have to adjust it by curve, not by "number of times" or by anything a carb says.

 

[Cobain03]

im not syaing your wrong, but thats what the instructions said

 

[Max Power]

OK, I reread your previous post, and I am guessing that the instructions for the adjustable vacuum advance referenced your carb by serial or model number, and then told you how many turns? Becuase in your first post you referenced numbers on your dizzy. It's kind of confusing.

OK, what you bought is a vacuum advance unit. Since there is a metal plate in your dizzy that also advances spark mechanically, the diaphragm is called a vacuum advance to avoid confusion.

Your initial question I believe was "Can I make it better?".

Maybe you can.

Read Hueys post above for a brief explanation. What your are looking for is a total advance curve that suits your engine and its modifications the best. Since that requires a bit of experimentation and a fair amount of dyno time, it is usually best to compare notes with people who have mods similar to yours and see what their curve is.

You basically want to run as much advance as possible to get the most power and economy whhile avoiding detonation. Do a Google on the key words and search here and I bet you will find plenty of info on advance curves for mild 302s.

BTW, did your old unit fail? I rarely see that.

 

[DJCarbine]

On a side note, if you are concerned about WOT and total advance, consider checking out the mechanical advance as that has more of an effect on wide open runs. I was lead to believe the vacuum timing unit was more for cruising manners at partial throttle.

The advance arms will have a 15 or 10 stamped on them if I remember correctly. If the 15 arm is used, thats 15*2=30 degrees timing added onto initial. My carb had a 13 and 18 arm on it for some odd reason, and I was getting 36 degrees added onto my initial.

If you are trying to get more peak power at the tip of the RPM range of the engine, I suggest looking into setting up your mechanical advance curve as well for a more aggressive timing curve.

Back to your post, the spark advance you got is obviously of the adjustable type. The adjustment will just change how the timing advance is brought on due to the load on the engine, and in turn affect the responsiveness of the engine either for better or worse depending on how you tune it. Or at least thats what I was taught, someone correct me if I am wrong.