Questions for the ignition timing gurus: from retard to advance (3 Viewers)

[DSRTRDR]

Steve,

that's what I suspect looking at SOR diagrams and the tech site (wish it would list some uniquely identifying parts; if you are only looking at one dizzy, it's hard to see what would make the difference); I just can't seem to figure out how it would be hooked up correctly for advance vacuum

 

[DSRTRDR]

You definitely need a different distributor: the nonUSA advance. You don't want to mix an advance carb port with a retard dizzy, or vice versa; things go the wrong way at the wrong time.

Also, on an advance dizzy the vacuum diaphragm points to the front. Retard dizzy diaphragm points to the back.

I assume with front and back you mean relative to the front of the truck/firewall? Diaphragm points towards the radiator in my truck.

 

[dvmotorsports]

Worked For Me

AZ emissions tests ALL vehicles in Maricopa country (Phoenix has a bad air problem) they are stricter in their testing requirements for older vehicles than California in that regard Nebraska couldn't care less, but there is no wheeling here

If there are some countys in AZ that don't require smog, get a PO Box there and register your car to the PO Box. I had a car that needed to be smogged in CA and it wouldn't pass. So i found out that there are two counties in CA that don't require it. I got a PO Box there and registered the car to it. When they asked why I was registering to a POB, I replied "I live in a rural area with no mail service, so we all have POB's"

Problemo Solvo!

Hope that helps.

 

[DSRTRDR]

No problemo smoggo..... problemo comprehendo dizzy - carb linky

I am aware of the 'out-of-county' trick, but I really don't want to travel that far for a stupid emissions test (particularly since I passed last time it took enormous retarding to the point where the truck would cough up any small hill on the 15 miles to the emissions station, but it passed needless to say, we advanced the timing as soon as we went wheeling the next time )

 

[IDave]

I assume with front and back you mean relative to the front of the truck/firewall? Diaphragm points towards the radiator in my truck.

That would be advance, then. Which is why it is plugged.

Some of those dizzies were both advance and retard. IIRC, the advance nipple is on the front/end of the diaphragm, retard nipple at the base.

 

[DSRTRDR]

uh oh, be careful with that nipple word ..........

but you do confirm my assessment of the dizzy

 

[Poser]

uh oh, be careful with that nipple word ..........

Why? Did he spell it wrong? ;p

 

[IDave]

uh oh, be careful with that nipple word ..........

So, do you have two nipples?.....





































....on your diaphragm?

 

[Poser]

Played with three, more than once, a few years ago....

 

[Pin_Head]

My '76 distributor is retarded, but then again, it is a CA cruiser.

 

[DSRTRDR]

if the fan on the engine is the same year as the dizzy, my set-up is from a truck that had an air condition (has extra pulley by fan); does that help narrow the year down?

 

[IDave]

Truck's in AZ, and you're not. Ja, Doctor C?

 

[65swb45]

Thanks for the heads up Dave!;p You guys just floor me sometimes! There are nowhere near enough hours in a day for a guy running a one-man shop with a home and social life to catch all these threads. If you want to start PMing me with threads you'd like me to comment on, I might have an easier time finding them!

Here are the basics of advance as I understand them. On a system that does not directly read from a crank trigger and imput-output spark from a computer, some system has to be devised to APPROXIMATE optimum spark timing. Spark timing needs to advance because the electricity travels at a constant speed from the distributor to the spark plugs, but the pistons inside the engine keep reaching TDC faster and faster as the engine speed goes up. Hence the need for advance.

Mechanical advance is good up to a point, and can be tinkered with to be made better. The factory mechanical advance in the ND dizzies never comes close to maximum efficiency, which is why so many people end up advancing their static timing so much to compensate for that shortcoming.

If you bump up the static timing, or increase the range and rate of the counterweights, at some point, at certain speeds, or certain loads, the mechanical advance may be providing more advance than is efficient, or even beneficial. At that point, a combination of heat and too much timing can cause predetonation [pinging] where you hear the pistons rattling from side to side in the cylinder walls as the gas begins to ignite too soon before the piston reaches TDC and tries to push the crankshaft backwards to it's normal rotation, causing the piston to take the brunt of the force between the two.

Therefore, it becomes advantageous to integrate a second tier of timing advance that is more load sensitive: vacuum advance. Under lighter loads, the higher vacuum of the engine will engage the diaphram on the dizzy and rotate the points plate counterclockwise, increasing the timing advance. Unlike the mechanical advance tho, under a sufficiently heavy load, the vacuum will be insufficient to maintain it's pull on the diaphram and will release it's hold on the points plate, allowing the timing to retard, and hopefully limiting predetonation.

Hth

Mark A.

 

[65swb45]

BTW, if you're gonna quote my FAQ, at least get the sections right! The basics of this explanation were actually covered under section 010.

And to answer Poser's question about the retard, well that's just it. The retard has the disadvantage of being a mechanical distributor for the vast majority of the time, requiring a lot of static timing advance at idle to not end up lagging far behind engine speed at higher RPMS. It also has the disadvantage that the most reliable way to give its diaphram a 'heavy load' signal would be to route it to the secondary side of the carb, which pretty much only opens under heavy throttle. Unfortunately, that is also the point at which there is usually insufficient vacuum to operate the diaphram on the distributor and retard the timing.

So if you bump up the static timing to keep it from 'dogging' at higher rpms, chances are it's not gonna retard nearly enough when you need it to, and it's gonna ping like a mofo as well.

Make sense?

[edit: glad to see you're both still logged in!]

 

[DSRTRDR]

Whow, that injects some heavy theory into the debate! Or should I say 'carbs' the topic ? Thanks for the background, Mark.

Now to the practical level - how is switching to advance going to affect emissions, and how do I hook up which lines, and do I plug the others?

Yes, Dave, truck is in AZ, therefore no pics.

 

[IDave]

*edit--beat me to it

sorry I missed the correct section: I thought there was more somewhere *


So, Mark, basically a retard-only dizzy will retard to avoid pinging, but won't function optimally under light loads?

Yeah, that's what you said while I was typing this post. Thanks, Mark!

 

[65swb45]

Whow, that injects some heavy theory into the debate! Or should I say 'carbs' the topic ? Thanks for the background, Mark.

Now to the practical level - how is switching to advance going to affect emissions, and how do I hook up which lines, and do I plug the others?

Yes, Dave, truck is in AZ, therefore no pics.

Ah yes! There was another point! As Pin_Head correctly pointed out, spark intensity, air fuel mixture, and internal engine heat have a lot more to do with emissions than timing. Changes in timing have the biggest effect on heat as far as emissions go. Soooooooo, the answer, as he alluded to, is that you've prolly already got an issue with at least one of these three things, and it would be hard to say whether changing dizzies would ameliorate or exacerbate the problem.

And as far as asking how to reroute emissions lines, I defer to one of Jim C.s classic lines: ".......and which office of the EPA do you work for?"

;p

 

[65swb45]

*edit--beat me to it

sorry I missed the correct section: I thought there was more somewhere *


So, Mark, basically a retard-only dizzy will retard to avoid pinging, but won't function optimally under light loads?

Yeah, that's what you said while I was typing this post. Thanks, Mark!

No, that's NOT what I said. The 'retard' dizzy SHOULD retard to avoid pinging, but it is marginal in that function. It will NEVER function optimally IMO.

 

[DSRTRDR]

sorry for the confusion, I didn't mean the emissions lines (all gone from my truck), I meant to ask about the vaccum lines between the dizzy and carb

as far as emissions go, I take it there is no other way than to just try and find out? Guess I will do that after the scheduled test then ;p nice, gives me more time

 

[IDave]

No, that's NOT what I said. The 'retard' dizzy SHOULD retard to avoid pinging, but it is marginal in that function. It will NEVER function optimally IMO.

So the retard's marginal at both advancing and retarding when it should.