Timing Advance

[TenSeven]

Adjusting the timing on my 2.8. Duraspark II, no smog, only PCV.

With the vacuum advance hose disconnected and plugged, at ~750rpm, the timing is 10 BTDC. With the advance re-connected the rpm's go up, after re-setting back to ~750rpm, the timing is now 26 BTDC. Is that normal?

I remember reading something about a 'total advance' of 36 but I thought that was at ~3500rpm. But maybe what I have now, 10 and 26, is good? (36)

Just to note, the vacuum advance is currently t'd in with the choke pull down.

 

[RonD]

You have 2 spark advances at work, vacuum advance and centrifugal advance.

Centrifugal is RPM only advance, this is the 36deg

Vacuum advance is engine load only advance.

Yes, you set base spark timing using only centrifugal advance, vacuum advance disconnected.
Engine also needs to be warmed up, choke fully opened.

10-12deg BTDC would be correct for stock cam/engine, centrifugal advance shouldn't change timing until about 1,000rpms, you can test this by increasing rpms slowly and watch for the advance to start.
As long as you are setting base timing with engine idling under 800rpms you will be OK.

Yes, when you add the vacuum advance back timing will advance and that is when you set the warm engine idle you want.

This is also when the tricky part starts, lol.
Because you can get hesitation when you quickly open the throttle, and this can be from spark advance issue or an air/fuel mix issue.
When you open the throttle extra fuel is squirted in by the Accelerator pump in the carb, the Richer fuel mix burns quicker so you want less vacuum advance, the ported vacuum you are using doesn't reduce vacuum advance as much as manifold vacuum would, it is more for cold engine use, but it still works.

 

[TenSeven]

As usual, thanks again Ron, I appreciate it

While setting the base timing I t'd off of the PCV vacuum port at the carb base but I swear it started running really rough for some reason (could had a vacuum leak somewhere at the 't') so I went back to the ported vacuum and it seemed to smooth out,?

While the vacuum advance line is plugged I'll rev the engine up and see if the timing is advancing. From what I gather I should see a stop in the advance after 2500rpm which at that time I'll note what the timing is.

 

[RonD]

You set base timing on warm engine, no vacuum advance, RPMs under 800.

Also one thing to keep in mind..........the "timing" plate and crank pulley mark(s) on the engine don't always exactly match true TDC, so grain of salt.

And yes increase engine RPMs up to 2,500+, NO vacuum advance, and you should see steady increase to about 34-36deg at around 3,000rpm from the centrifugal advance

Lets say you set it at 10deg Before TDC as base spark timing
Manifold Vacuum advance should add 10-15deg to that, so connect vacuum hose from manifold to distributor and check timing again.
If it shows 25deg but engine is running rough it could be air/fuel mix is too Rich, so burning too fast for 25deg BTDC spark timing.
Rich mix burns faster than lean mix, idle should be leaner mix.

So with a carb you need to adjust both spark and air/fuel at the same time.
And it could be too much vacuum advance so you want to adjust it down to only add 10-12deg

The Duraspark vacuum advance canister should have an Allan key(hex key) adjustment.
It is inside the hose connection, remove the hose and insert a 3/32-in. Allen wrench, you should feel it slide into the head of the adjuster.
Counter-clockwise reduces advance, clockwise increases advance.
General rule of thumb on this is to turn it clockwise until you get pinging, then counter-clockwise for 2 full turns to set it

Ported vacuum is different, as said, and it has been quite a few years since I have tried to time one.
It will 0 to 4 deg advance when connected, when you open the throttle it should advance a bit more then then stop and all you have is the centrifugal advance at a steady higher RPM

 

[TenSeven]

Thanks Ron.

Interesting stuff actually.

Looks like adjusting the mixture being my other task to check off will go right along with setting the timing. I think I'll connect the vacuum advance back over to manifold (using the PCV vacuum port). Seems, as you've noted, the ported (I've also seen it called 'adjustable') vacuum port was more for EPA reasons than performance. Since I got rid of all the EPA junk (sans the PCV valve, which actually I could probably replace with just a breather) I'm not too concerned with anything that's going to bog down the engine.

 

[RonD]

PCV valve helps stop oil from leaking from valve covers and oil pan gaskets

It keeps a slightly negative pressure in those areas, so slows possible seeping which becomes a leak over time.

 

[TenSeven]

PCV valve helps stop oil from leaking from valve covers and oil pan gaskets

It keeps a slightly negative pressure in those areas, so slows possible seeping which becomes a leak over time.

Ah, I see. Does the PCV valve 'need' manifold vacuum or can I leave the PCV valve in place but route it's hose behind the engine? I'd like to use the PCV port on the carb just for the distributor advance. If the PCV needs manifold vacuum to work, then I'll 't' it off.

 

[TenSeven]

Actually, after reading a bit I better keep the PCV connected to vacuum, too important, as you noted, to keeping the engine vented.

I'll just 't' off the PCV vacuum port to supply the dist. advance with manifold vacuum.

 

[TenSeven]

One other thing I've come across on the net is finding out that the distributor recommended in the TRS 2.8 Duraspark Conversion article might be non-adjustable and has a tendency to apply too much advance. I could be stuck with the advance its putting out.

Also, I hadn't heard of it before but I read some distributors are ment to be used with only ported or only manifold vacuum.?

http://www.oreillyauto.com/site/c/d...ck=Search_02780_1135235_-1&pt=02780&ppt=C0334

Anyone using the Cardone Remanufactured Distributor recommended in the TRS article? Any problems with timing advance? Using ported or manifold vacuum?

 

[TenSeven]

Messed around with the timing today.

At operating temp, vacuum advance disconnected and the hose plugged, and ~750rpm, here's what I'm getting...

At Idle. Degrees 10 12 14
At 2600rpm. Degrees. 30 32 34

'Seems' to run fine on all three (can't road test it till I get a driveshaft). It's a stock motor, no emissions, should I just stick with the 10 BTDC? Is 30 degrees enough? I thought it should be about 36?

 

[RonD]

Inside the distributor there is a "reluctor arm" it will have different settings/places.
10L = 20deg of centrifugal advance
So 10deg BTDC base, with 10L reluctor = 30 deg advance at max

12L would be + 24deg of advance
8L +16deg

So it isn't an automatic, "it should be 36deg at 3,000"

Timing is very engine specific and use specific, hauling loads, racing and daily driver are different uses.

Have a read here: http://vb.foureyedpride.com/showthread.php?22229-The-Ultimate-Duraspark-Distributor-Timing-Guide

it has much of the stuff covered but is Duraspark specific where my knowledge is more general.

 

[TenSeven]

Thanks Ron.

its my understanding the the Cardone distributor I have is non-adjustable, but I think that's referencing the the diaphragm isn't adjustable but I think the reluctor arm, springs or cam may be adjustable/replaced for a better curve.

Thanks for the link, I'll check it out.