70 911T Distributor/Timing problem

[JM70911T]

Car: 70 911T 2.2 w/ Zenith Carbs Bosch distributor

Problem: Runs but very rough.

Carbs have been recently rebuilt but my current focus is on the engine timing. Before I look at dialing in the carbs I want to ensure that the timing is correct.

Here is what I have done:
1. Set static timing according to Pelican tech article. Engine starts but runs roughly.

2. Checked idle timing using a timing light. Currently is firing for #1 almost at ~30 degrees BTDC not at 5 degrees BTDC. (ie 30 degrees after Z1 mark.

3. Tried rotating the distributor to adjust the timing by loosening the 13 mm bolt.

However the range of adjustment doesn't get me in the 5 degrees BTDC range.

Any ideas of how to get the distributor setup correctly to achieve the correct advance for idle ?

Any help would be greatly appreciated.

Regards,

Jon

[Steve@Rennsport]

Jon:

The most important aspect of timing a 911 (pre-smog) is total advance at 6K RPM. Thats all that matters as long as the advance mechanism inside the distributor is functioning properly.

Set total advance (34-35 deg) at 6K since all the centrifugal should be in by then. After that is set, use your timing light to confirm idle timing and whether the advance weights are working or not.

Given the age of these distributors, its not uncommon to find sticking advance weights that will play hell with timing values and drivability.

[Walter_Middie]

Jon,

I think you are saying that you cannot turn your distributor far enough to get the correct initial timing. The following thread talked Kach22i through re-indexing his distributor when he had the same problem. Look down about 1/2 way on the first page of this thread to pick up where Kach22i asked about his problem:

JWalker + 35Deg + 3.5CO = HP

[Early_S_Man]

Jon,

The gear on the distributor is probably off one tooth with respect to the gear on the crankshaft ... quite easy to do and not at all hard to correct! Here is my suggestion for a comprehensive distributor maintenance [seriously neglected on most engines] proceedure ... at the same time as curing your running problems because of the timing being off:

1. Turn the engine over by the alternator nut until Z1 is lined up with the notch in the fan housing and the distributor rotor is in the vicinity of the #1 spark plug wire notch on the body of the distributor.

2. Loosen 13 mm nut completely until distributor body is easy to move about. Clean thoroughly around the base of the distributor so no gunk will fall down into engine!

3. Remove trigger wire to CDI unit and distributor cap.

4. Pull distributor out of the case.

5. While you have the distributor out ... clean thoroughly the internal parts after partial disassembly, which means removal of the point plate. An exploded diagram is included in the following thread:

distributor lube...

6. Inspect for excess play of the shaft bushings and worn out or missing shims and fiber washers. Stoddard NLA-602-101-50 shim kit will have several usable parts, or some may be obtained locally at a motor/alternator rebuild shop.

7. Check for rust or gunk collection/buildup causing the centrifugal advance mechanism to stick rather than move smoothly and return normally by the springs. Clean with Brakleen or similar spray degreaser, then lubricate with engine oil.

8. If the Bakelite wafer sliding surface for the centrifugal weights has broken apart or is missing, order NLA-602-102-00 Teflon repacement from Stoddards on the following page:

http://www.*************/shop/shopdisplayproducts.asp?id=125&cat=Engine+Electrical

9. Be sure to use engine oil on the gear shaft before reassembling the cam and rotor shaft over the centrifugal advance mechanism.

When you are ready to reinstall the distributor ... the following thread has several tips on setting the timing:

JWalker + 35Deg + 3.5CO = HP

Good luck!

[911pcars]

"Problem: Runs but very rough."

Did the engine work okay before rebuilding the carbs? If so, I'd look at this area.

If the timing is a little off, this will not necessarily cause the engine to run very rough. I'd look for a misfire somewhere in the secondary ignition system (spark plug, spark plug wire, distributor cap, ignition coil, etc.).

Is the compression okay? Verify this first, otherwise you'll be going in circles.

Sherwood

[JM70911T]

All: Thanks for the suggestions. The posts have given me some things to drill into a little more extensively.

I will look into the distributor's condition this week. Although it looks almost new. Compression is another metric that may help identify issues (leak down yielded favorable results).

This car is quite difficult because I bought it as a project car without much background on the engine. The previous owner claimed top end was re-built along with other upgrades..but who knows. The condition of the engine appearance wise does back the story up.

The price tag for the car was around 3k with a tight body so can't complain too much i guess.

Since it has never run correctly in my possesion I have no baseline to go by.

I have slowly worked through a bunch of issues including annoying oil leaks (resolved, painfully), gummed up carburetors (rebuilt) and now timing that is clearly not quite right.

One issue that I fixed tonight is that the #5 plug wire was located at the notch on the distibutor (instead of #1) with the rest of the plug wires in the correct order. I put the wires in the right order and pulled the distributor out to align with the notch (@ #1) (as opposed to an arbitrary point on the distributor aligned with where #1 used to be). I am not sure why the PO had the wires like this.

I can't start the car to test tonight..the neighbors don't seem to enjoy the sound of a fine german sports car winding up quite the way I do : )

I will give an update when I make some progress.

Regards,

Jon

[azasadny]

Jon,
Any updates?

[JM70911T]

Update: I figured out how I can adjust the distributor more to get the car timed correctly.
After getting the timing right and synchronizing the carbs the car is running better but is still running a bit rough (pops and skips).

I think the pops are from an exhaust manifold leak.

I am going to work on the car more this week and will post my findings.

Regards,

Jon

[JM70911T]

On monday night I finally got the engine running correctly. I was more than a little psyched !

Here is a list of actions I took that fixed the extremely rough running engine:

1) Reset timing and dwell, installed new plugs.

2) Fixed an exhaust manifold leak on the right side of the motor. Turns out I never torked down the nuts last winter when I had the engine out ? This is what happens when you can only work on the car in brief 2 hour increments !

3) Worked through the process of tuning the Zenith carbs which I rebuilt last winter. Looks like I got the rebuild right : )

Then magically the Porsche gods were on my side and the engine was idling beautifully and winding right up. Since I purchased the car with issues I never heard how great the engine sounds.

What a great sound : )

I was strarting to loose patience with this car but now it looks like I am on track to get the car on the road in the next month or so !

Thanks to Pelican Parts for the great technical resources and all the helpful members who provided insight into potential causes.

Without these resource I would not be able to own this car.

Jon

[Early_S_Man]

Jon,

Glad you were able to work the problem and get it running close to perfect. Careful, methodical methods can yield amazing results on these cars!

Sometimes, inexpensive parts can achieve very significant improvements ... case in point -- yesterday I replaced the spark plug wires and oxygen sensor on my sister's 1989 Chevy Suburban ... $17.82 NAPA economy MileagePlus tm Spark Plug Wire Set, and $21.52 Bosch 12014 OEM O2 sensor. Results were instant and dramatic ... getting rid of an intermittent hesitation and miss problem! Both were the originals on that engine ... with 350K+ miles on them.