Help identifying timing marks on a built 72 or 73 T motor

[tommott]

Trying to tune/check the timing on my 914/6 conversion. Suffice to say it's a PITA. I'm attempting to transpose the timing marks on the fan pulley to inside the little viewing window on top of the 901 transmission to make things easier.

I'm trying to ascertain which mark pictured below is TDC? Through a bunch of searching here there seems to be a bevy of different timing marks on a bevy of different engines. The common denominator being the Z1 mark is always TDC. The motor in the car is a built up 72/73 T motor with big cams, compression, ect, ect giving me little confidence that the pulley on the car is the stock pulley....further complicating matters.

My pulley marks are pictured below. The pics leave a bit to be desired but with the working space between the firewall and the pulley itself it was the best I could do. I can make out the 30 and 35 degree marks for the advance and can make out a Z with one mark....and perhaps a 1 with another mark....but not a Z1 with just one mark. I'm not 100% sure which mark is TDC and which mark is for 5 degrees before or after center. My hunch is that the mark on the left is TDC but just want to be certain.

Any help would be appreciated.

[cmcfaul]

The second notch on the left is TDC. The one to the left is 5 degrees after TDC. The ones to the right are max advance marks Before TDC).

Chri

73 911 E

[tommott]

Thanks Chris. Glad I didn't go with my hunch.

[cmcfaul]

It can be a bit confusing. With the vacuum retard connected the correct timing at idle is 5 degrees after TDC. That’s why the notch is there. It should advance all the way to the right as RPM's increase.

Chris
73 911 E

[tommott]

Wow!

As I was resurrecting a previous thread of mine asking about why my vacuum line was missing apparently you were posting on the very same subject on this one.

For some reason my vacuum is not attached, and I don't see an unaccounted line anywhere. I don't even see where a line would originate from the intake manifold.

Should my car definitively have a vacuum run distributor? If so where would the line originate from? It looks like my 911/51 72-73 T motor would have originally had mechanical injection, but now has Webers, which I assume were swapped during the build of the motor. Perhaps the vacuum was no longer needed after this swap?

[cmcfaul]

Does it have MFI (mechanical fuel injection)? If yes, the line connects to the right throttle body, travels over the fan housing to the connecter on the disributor. I can take a picture if you like.

Chris

73 911 E

[tommott]

Originally Posted by cmcfaul

Does it have MFI (mechanical fuel injection)? If yes, the line connects to the right throttle body, travels over the fan housing to the connecter on the disributor. I can take a picture if you like.

Chris

73 911 E

Chris,

It does not have MFI. It was swapped over to Webers. Do you happen to know if you don't run vacuum retard and/or advance on these motors when running Webers?

[cmcfaul]

Should not be a big deal. What you need to do is set timing to the optimum full advance and see where if falls at idle. 5 degrees BTDC would be ideal in this sceanaro. Most important is the full advance. Once that is set, if it idles OK you should be good to go.

Setting the full advance is always fun. Rev the shi...t out of it until the timing stops advancing and hope she holds together ;-)

Chris

73 911 E

[tommott]

Checked the advance. Now keep in mind these are very rough figures as I am literally working off my feet, with the engine lid removed so my fortunately non-bulbous head fits in the engine compartment, looking off a mirror that is still a good ways off in the distance from my eyeballs,.... but it looks like I got the total advance somewhere between 30-35 degrees BTDC +/- a couple degrees.

However, with the total advance set in that range, it looks like the timing at idle, around 900 rpms, is somewhere around 10 BTDC +/- a couple degrees....perhaps a couple more on the + side. Not sure if this is enough of difference to warrant being prescribed as an 'issue;', or possible indicates that my distributor may have some sort of vacuum retard that should be, and is obviously not currently, hooked up? Seems to be rich at idle, but the carbs still need to be set up. In fact I'm setting timing SO I can properly tune the carbs.

[E Sully]

Here is a little infomation. Clear picture of the pulley marks. The FE is for setting the MFI, uneeded now with carbs. It would be good if you can find out from the Previous Owner if it is stock or if any changes were made aside from the carbs.
Make sure the points are good and the advance weights move freely, a little oil on the felt pad also. Set the initial gap on the points and then fine tune it with a dwell meter. Dwell for Bosch is 38 and if Marelli 40. Max advance is more important than idle, you don't want too much. You could test the vacuum pod by putting suction on it with your mouth with a rubber hose to see if it changes. 5 ATDC at 900 rpm is with vacuum operating.
Distributor Maintenance

[Flat6pac]

The vacuum is simply a retard on the timing for emissions. With carbs you dont have anything to plug into. If you were carbed, the hose would be from the intake manifold of #1 and #4. You would drill a hole and install a pipe for vacuum line. T the 2 vacuum lines together then to the distributor. The vacuum only works when the butterfly is closed.
Bruce

[tommott]

Appreciate the replies.....and happy Thanksgiving all!

So I shouldn't have anything to worry about if the timing at idle is around 10 degrees BTDC, just as long as I have the total advance at 30-35 degrees BTDC +/-?