Timing help for 2.7
 

Does anyone know the proper ignition timing at idle for a '74 2.7t?
In the different maintenence guides I have, there are references to both 5atdc and Z1 (both with vac hose attached) Thanks

Does your distributor have only one vacuum dashpot? If so, then I think that it's a vacuum retard, like that originally on my '77 2.7. It's there to retard the timing at idle to reduce emissions. Easy enough to check: with the engine idling, disconnect the line and see which way the timing moves. If it is a vacuum retard, the engine will run better if this line is plugged-off and rendered inoperable. For starters, set the timing to TDC at idle around 950 rpm. Then check it at 6000 rpm, it should be around 35 deg BTDC. If not, then adjust the timing until it's at 35 deg BTDC at 6000 rpm. For reference, the factory was nice enough to put a mark on the flywheel pulley for 35 degrees BTDC.

Ed Cavalier
77 911 Targa

Yes, it only has one vac line that retards the timing. So TDC is the correct idle timing?

Any downside to disconnecting the vac retard? How did you plug the line?

my ignition curve was a smog gizmo.. so the engine runs smoother at lower rpms and cooler. In desert heat listen for pinging at lower rpms.. if pinging drop timing in 2deg steps

The only downside is increased emissions. I plugged the line by cutting it and then "reconnecting" it with a piece of wooden dowel. It's somewhat hard to believe, but there's actually a factory part for plugging this line. There's a picture of it in the factory manual. TDC at idle is a good place to start, but the important measurement is advance at 6000 rpm. If you don't get 35 deg at 6000 rpm, you're leaving hp on the table.

I've got it at about 36 deg, but it's not steady. It kind of wobbles between 35 and 37. Is this normal? Also, if I disconnect the vac line it moves the timing 10 -12 deg. It seems if I adjust it back to TDC without the vac line it will throw off my advance. Thanks for everyone's advice - this is my first time to set the timing.

Bart,

5° ATDC is the idle timing at 900 rpm with the vacuum connected to the retard module. Without vacuum module connected, and with vac. line plugged it would be 5° BTDC, since the vac. retard is 10° total.

The specs for a '74 2.7 is identical to the '72 - '73 911T engine ... posted in the following thread ... I suggest checking your advance curve per the factory data ...

http://forums.pelicanparts.com/showthread.php?s=&threadid=5432&highlight=distribu tor+lube

Jittery timing at max advance suggests wear in the distributor, or dirty advance mechanism. I suggest pulling the distributor at TDC #1, and full disassembly, cleaning, and inspection for wear. Visible play ... either at cam or drive gear can be addressed after disassembly. New fiber thrust washers, shims, or spring washers ... or shaft oilite bushings may be needed.

Warren,
Thanks. The earlier post is great - I will definitely print that out for future reference.