Timing on a non-stock motor with PMO carbs

[JordanPryce]

I'm looking for advice on where to time my motor since switching to PMO carbs.

Engine specs are as follows:

1977 911S case with 8.5:1 pistons, e-cams, 911S heads, Mahle 8.5:1 pistons
classic retrofit CDI+ ignition
Stock Bosch (clockwise) distributor with vacuum unit (not hooked up)
PMO 40mm carbs jetted 145M, F11 tubes, 180 correctors, 55 idle
The pulley is marked at 15 ATDC, 5 ATDC Z1 (TDC) and 35 BTDC.

Since the motor was assembled from parts, and is also not a stock configuration, I'm wondering if I am missing a mark at 5 BTDC. Knowing that I should time to about 32 BTDC at full advance, and that I'm currently timed a 5 ATDC and idling lousy and also falling short of 32 BTDC when revved hard, am I safe to move towards 5 BTDC and see? I want to eliminate timing issues before moving on to carburetor.

Current symptoms are a hunting idle, and popping on acceleration through 2,900 RPM's.

[Steve@Rennsport]

Hi,

Ideally, you want 32-33 degrees at 6K and 10 degrees at idle, however your distributor likely needs to be recurved to permit this.

[JordanPryce]

Thanks Steve, The previous owner said he thinks that it's been recurved already. So to be clear, I'm looking for 10 degrees BTDC not ATDC right?

[Steve@Rennsport]

Originally Posted by JordanPryce

Thanks Steve, The previous owner said he thinks that it's been recurved already. So to be clear, I'm looking for 10 degrees BTDC not ATDC right?

Yessir, thats correct.

[JordanPryce]

Ok, I can't advance much beyond TDC because I'm hitting the 35 degree mark at about 4,000 RPMs. I suppose I now have to decide whether to recurve my distributor or run a custom map on my CDI+ (Classic Retrofit)

[Flat6pac]

The vacuum is retard, not advance. With carbs you don't connect.
Bruce

[JordanPryce]

Right, vacuum is not connected.

[zedsn]

My pulley too is off on my hotrod 2.7 and I didn't build the motor so I don't know why. I ended up timing the engine by trial and error even before I had a recurve done on my distributor and kept the timing the same once I got the recurve done.

[JordanPryce]

Originally Posted by zedsn

My pulley too is off on my hotrod 2.7 and I didn't build the motor so I don't know why. I ended up timing the engine by trial and error even before I had a recurve done on my distributor and kept the timing the same once I got the recurve done.

Interesting. What do your numbers look like now and who did your distributor?

[zedsn]

I had a flat spot in my power band that is gone now. Kinda like the car was stuggling to reach my 7300 redline but the guy whos name is Dan from Arizona recurved my distributor and ran different springs and I am very happy with the car now. I am running a MSD box, pertronix and a msd coil with my weber IDA carbs.

[JordanPryce]

Update. I acquired a 004 RS distributor with the proper curve. Worth the ridiculous price. The car runs, idles and pulls like a dream.

[Jonny H]

Hi Jordan,

Remember you can overlay advance to optimise the distributor curve using the CDI+ software. This is best done on a chassis dyno. See 'overlay mode' in the manual, downloadable here:

911 CDI+ (6 Pin) - Classic Retrofit