Another MSD timing question....

[uk409deuce]

Not wanting to hijack Nuts thread I am having similar issues..... I just this week installed an MSD and am a little confused. Heres what I got..

425/409 Factory dual quads Z11 Hydraulic cam. This is a stick car.

Heres what I did...

Disconnect vacuum pipe, set initial to 12 degrees. When the throttle is opened quickly the timing bounces to retard before advancing.. then hook up the vac pipe and the timing goes up to about 24 degrees at idle and then 38+ total. Open throttle quickly and it still bounces back to around 0 before advancing.

Also I only just noticed the vac pipe is hooked up to the rear of the front carb which is on a factory style progressive linkage, is this right? I always thought the idea of vacuum advance was for part throttle situations which would mean that the throttle plates on the front carb might not be open??

Also I don't think it is a carb issue as I put about 5000 miles on it last year with a factory single point distributor with no issues.

Words of wisdom greatfully accepted... as I am off to the track on Saturday to run it through for the first time...:beerbang

Gary.

[Nuts]

Gary,

I have noticed a similar drop in advance since putting in the MSD. I didn't check for that before, with the Mallory or the stock distributor so I can't say if it is standard ?

Sounds like you are hooked up to manifold vacuum, like the stock distributor would have been. I have tried both ways and mine seems to run a little better on the ported vacuum. But I haven't had the chance to try it out at highway speeds yet.

Good luck and I hope you get some good advice, I'll be watching >>>>

[fatride]

Gary, what rpm is the engine idling at? It sounds like you are pulling some mechanical advance at idle. When the throttle is opened quickly you may have a slight bogg that drops the rpm slightly, enough to drop off the mechanical advance. Try some heavier advance springs and try seting the timing at 600/650 rpm. 24 dgs at idle is fine, but remember even when you have the timing set properly you will still drop to initial timing when the throttle is cracked full open at low rpm when you use the vacuum pot hooked to manifold vacuum! I have my MSD set at 20 dgs initial and 36 total. I have to limit the vacuum advance with the stock MSD dist or it will pull to much advance at idle and at light cruise. If you use an adjustable vacuum advance you can limit the advance pull and adjust the pot to pull advance at a higher vacuum than your engine at idle and then you can still use manifold vacuum. If you use the MSD nonadjustable vacuum can you can limit the pull length and use a ported/timed vacuum port and pull advance at light cruise only.

[desapience]

Not wanting to hijack Nuts thread I am having similar issues..... I just this week installed an MSD and am a little confused. Heres what I got..

425/409 Factory dual quads Z11 Hydraulic cam. This is a stick car.

Heres what I did...

Disconnect vacuum pipe, set initial to 12 degrees. When the throttle is opened quickly the timing bounces to retard before advancing.. then hook up the vac pipe and the timing goes up to about 24 degrees at idle and then 38+ total. Open throttle quickly and it still bounces back to around 0 before advancing.

Also I only just noticed the vac pipe is hooked up to the rear of the front carb which is on a factory style progressive linkage, is this right? I always thought the idea of vacuum advance was for part throttle situations which would mean that the throttle plates on the front carb might not be open??

Also I don't think it is a carb issue as I put about 5000 miles on it last year with a factory single point distributor with no issues.

Words of wisdom greatfully accepted... as I am off to the track on Saturday to run it through for the first time...:beerbang

Gary.

Gary,

I'm assuming you are NOT using any kind of ignition box with this new MDS.

First, did you change anything or take anything apart on the distributor before installing it? If so, go back and make certain everything was properly re-assembled.

Second, if you changed them, what advance springs are you using now? Are you using what the MSD came with out-of-the box? If so, you have two heavy silvers on it now, and thus not likely into the mechanical advance on low idle, and also not likely into the mechanical coming right off idle.

If you've already gone to too light a set of springs, like the two light siilvers, or a mix of one blue and one heavy silver, go back with the two heavy silvers (for now), as your starting point. Do not over-look going back to check the springs now -- one may have fallen off if you changed anything already.

Set your initial timing at 12 degrees at a good low idle, making certain there is no chance the mechanical advance is in play (do this with ALL the vacuum ports blocked off). Now, hook up your vacuum line to a ported vacuum source.

Start the car again... how does it run now? Check the timing again -- the timing should not budge from intial on idle since the vacuum source is timed. Idle speed should also remain ~constant.

Now, when you crack the throttle open "quickly" does the advance retard?
Does it bog down?

On the good assumption that at a low idle 500-600, with two heavy springs in place, even if the engine bogs, it should NOT retard at all be because of a disruption in the mechanical advance, because it should NOT yet be in play!

If all is right with the timed vacuum port working correctly, and the advance springs are on correctly (two heavy silvers for the start-point), and you've properly set the initial timing at 12-13.. . the bog is likely originating from your carbs, the accelrator pump(s), fuel pressure, clogged filter, linkages, etc...

If you determine some sort of carb malfunction, fix it NOW before you go forward to changing the advance curve...

Once you are sure the carb(s) are okay.. now take on the changing of the advance springs (to shift the advance curve to come-in quicker, and at a greater rate of change. There's a great graph in the MSD manual to follow along.

STONGEST TO WEAKEST, is as follows (read your manual, it's a good one)

STRONGEST: two heavy silvers.
NEXT STRONGEST: one blue and one heavey silver
NEXT DOWN THE TIER: two blues
NEXT DOWN: one blue, one light silver
NEXT DOWN : two light silver

You can also play with only putting one spring only (any color)... but, one of the above pairings will work nicely for you.

IF I were you, I'd go to the two blues, then drive the car and check for detonation (pinging). If you have ANY pinging what-so-ever, then, go up to one blue and one heavy silver.

Hope his helps solve your difficulty.

Denis

[fatride]

With an initial advance of 10/12 dgs and the vacuum pot hooked to a timed port I would be surprised to hear that the idle quality will be acceptable. Moving the vacuum line to manifold vacuum (if you have enough vacuum at idle) will advance the timing to around 20+ dgs. This should improve idle quality. Most of the time advancing the timing at idle will bring the rpms up, this will allow you to back off the curb idle screw which will improve throttle response, in some cases, with the timing retarded at idle, the throttle blades will be out of the idle circut. This will lead to an overly rich idle that will burn your eyes make for a soggy launch and foul plugs. With an auto tranny when you load the engine at idle by placing the tranny in gear the engine will stall! Give both methods a chance and see what works best for your engine combo. Remember that the timed port vacuum advance idea was a lame attempt by Detroit to sidestep pollution issues. :deal

(If anyone disagrees with me I take it all back)

[Ronnie Russell]

What Ray said........ Simple, basic, to the point, and true. IMO :cheers

[dq409]

Yep !!! What ray said !!:clap

Ya no,,,, this Ray guy is getting smarter all the time,,:rofl

Paul (garbageman) , Give a try to what Ray has just mentioned to your car and see if it helps your launch,,, dq

[fatride]

I hold the option of disagreeing with myself on occasion, this is one of those times! I guess there is an exception to every rule. In my case, and I'm sure others, When you have 20 dgs initial advance and 34/36 total, this may be a case where you would not want additional advance at idle. In this case I could see where you may want to use a timed or ported vacuum source that would only pull additional advance at light cruise. I myself do not trust the timed port to not add
vacuum advance at WOT. I will add an adjustable vacuum advance unit to my MSD ready to run distributor (I can't belive for the money spent that it did not come with an adjustable unit!) MY 409 idles with 12/13" of vacuum. I will adjust my vacuum pot to start pulling additonal timing at cruise vacuum. That way I will not feel the need to disconnect the line at the strip.

[uk409deuce]

Thanks for the input, I just spent a little more time on it, idle is 670rpm when setting initial. I have set the initial to 12 and when the vacuum is connected I have 24ish at idle. So I am going to leave it and have a drive tomorrow and see what happens.

I am using a Snap On digital light, a few people have told me to junk it for a conventional one when timing an MSD? Ever heard anything abount them being inaccurate???

Thanks again.
Gary

[desapience]

I hold the option of disagreeing with myself on occasion, this is one of those times! I guess there is an exception to every rule. In my case, and I'm sure others, When you have 20 dgs initial advance and 34/36 total, this may be a case where you would not want additional advance at idle. In this case I could see where you may want to use a timed or ported vacuum source that would only pull additional advance at light cruise. I myself do not trust the timed port to not add
vacuum advance at WOT. I will add an adjustable vacuum advance unit to my MSD ready to run distributor (I can't belive for the money spent that it did not come with an adjustable unit!) MY 409 idles with 12/13" of vacuum. I will adjust my vacuum pot to start pulling additonal timing at cruise vacuum. That way I will not feel the need to disconnect the line at the strip.

My input for Gary was aimed at trying to establish a start-point for him to sort-out potential carb problems, idle vaccum problems, etc., by completely separating any over-lapping sources of advance forces.

The issue of whether or not to use a timed or non-timed vacuum port is one of fine tuning to a particular application and engine/tranny combo, as well as to what purposes you are likely to use the car (racing, etc.).

I've personally always liked the non-timed porting for a vacuum advance, and I agree with you about the MSD 8393 being a bit lacking by not already having a fully adjustable vacuum pot...

Whatever the situation at idle, I want the mechanical advance to start coming in virtually immediately right off idle, regardless if the vaccum advance is connected to a timed or non-timed vacuum port. IF it is connected to a non-timed port, and with the resulting timing at that idle point being 20-ish (about 8 degrees made for by the vacuum advance), and knowing that when cracking the throttle, vacuum is going to abruptly drop, I want mechanical advance springs that would be of a strength enough to have no part in that 20-ish range (at idle speed, obviously), but light enough for the mechanical advance to immediately kick in to take over those 8 degrees that were held by vacuum at idle speed (meaning your springs should be light, with the engine not prone to pinging at that rapid a shift in timing curve).

IF the springs are too strong, and with the abrupt drop in vacuum when you significantly crack the throttle, the mechanical advance will be lagging until rpm's come up. It is at that point that we'd likely see the timing light read a transient retarding of timing before the mechanical advance kicked in. There would not be a smooth transistion reflected in the timing curve changes (if you drew a graph of it all, it would not be a smooth sloping upward line, in this case).

This is the beauty of having certain computerized ignition boxes to help overcome this "bumpy" transisiton, and the "ugliness" of doing without one.

Like you, I'm not so sure in trusting the timed-port connection to provide or not provide the WOT cruise-speed vacuum, as you would a non-timed port. But, that's how it is supposed to work!

You also mentioned idle quality, by going to a non-timed port -- to get 20-ish intial timing at idle speed. You would also get a slightly cooler running engine at idle with a more advanced timing -- at idle -- yet not too far an advanced initial timing when you first crank over the starter. And, as you also mentioned, a car with an auto tranny would more easily resist stalling after a quick return to idle speed from a cracked open throttle run.

Lots of trial and error... finding the right combo for your own combo requires an understanding of how to make what you have work best for you.

While there is no set formula for everyone's ride, there is a formula for finding the one best for you.

Denis

[desapience]

Go to this link... read both pages.

http://www.mustangandfords.com/techarticles/mufp_0505_ignition_basics/

Denis