Single Distributor Car - PM1-4 or +6, what should Plug #1 point at?

I have an ongoing minor crisis of confidence. Considering I've done this process in the past it's never something I've thought about or in fact remembered. I have googled furiously and I cannot get the definitive answer. I can make arguments for both options. I'm hoping that my current set up is wrong as that would explain my current woe!

Single Distributor Car
If the distributor 'point' is aligned with the red mark on the distributor casing (i.e. Cylinder #1)
Where should the indicator on the flywheel be pointing?

a) PM1-4
b) +6

Thanks very much
Andy

 

Thanks for the reply, I thought my thread was going to die a lonely death!

 

Hi Steve,
You may wish that you hadn't ask...

I have the electronic trigger system.
Towards the end of last year I found that the car would accelerate and drive fine for a while but then, like a switch being flicked, it would get 'stuck' at around 4,000rpm and pressing the throttle would make no difference.
Then after anything between a few seconds and a few minutes, the switch would be flicked and the car would leap to 5,000 rpm or wherever the throttle was being pushed to - and the car would be fine.

I have worked through this methodically.
1. I cleaned and lubricated the throttle pedal and the entire mechanism through to the carb linkages - to make sure nothing was physically sticking.
2. I tested the plug leads and found one was faulty - I replaced the entire set. But the problem persisted.
3. I cleaned and relubricated the advance/retard mechanism being very careful to make sure the springs etc. all went back as they came out.
4. I checked that the distributor contacts weren't burnt and were clean.
5. When I reinstalled the advance/retard mechanism and the distributor, I positioned the flywheel to sit on the +6 mark and then attached the distributor such that it was pointing at #1 cylinder (i.e. with the engine not running)
6. I tested the carbs for air leaks but found none (and the problem was at higher revs not lower revs - the air leak would be more evident at lower revs)
7. I tested the VR Sensors - one was showing 1,000 ohms resistance (should be 700) - so these were replaced and adjusted to be the required clearance from the reluctor. I also replaced the coils at the same time but this was probably unnecessary.

At this point the car was starting fine. I set the idle to 900 rpm and the timing light showed the car was sitting bang on the +6 mark. I assumed the problem was cured.
But out on the road, again at first the car was fine but after a few miles the problem at 4000 rpm returned.

My thinking at this point was that this problem was heat related. As the various parts heated up (i.e. after a few miles drivng) the failure occurred. The most heat sensitive parts are the ignition modules. So I got a new pair of Hella ignition modules and installed them. I double.triple checked all the wiring has gone back correctly (King Leads/Plug Leads/Coil power/earth etc.). I've put a timing light on all the leads and they are all getting a spark.

However, the car fires up but is now idling roughly at 500 rpm and misfires if I push the throttle.
I pulled all the plugs and they were oiled (probably from driving around with the problem at 4000 rpm). I cleaned the plugs but the problem persists.

A new set of plugs seems the most obvious next step - there is nothing else to replace!

I didn't actually check that I was on the compression stroke when I set TDC but the fact that the car was running smoothly before I replaced the ignition modules suggests that I got lucky?
If the timing was 180 degrees out, would it even start?

 

Thanks very much. Some very good ideas there.

Just to clarify the 'sticking' at 4000 rpm problem, as this may help.
If I was to gradually accelerate and continue pushing the throttle until the engine should be hitting 5000 rpm.
- at 4000 rpm the engine note would change (into more of a thrum/drone sort of noise) BUT the revs would not increase, despite me pressing the pedal further.
- at some point (seconds/minutes) the revs would suddenly leap to 5000 rpm (i.e. where I was expecting them to be on that amount of throttle) and the engine note would return to normal.

My first instinct was that it was a mechanical problem. BUT this problem would only manifest itself after a few miles of driving. This has lead me to my latest theory - i.e. that it is temperate related.
Also, and I've just realised this following writing it down above, the fact that the engine note would change at 4000 rpm but the revs did not increase, suggests to me that actual throttle mechanism aren't the problem - I think that the carbs are opening up and dumping more fuel in but it's not getting burnt or burnt at the right time.

No need to reply to this with any haste. I am going to work through your suggestions and do a bit more thinking!

 

I did test the pump when the car was cold and it was delivering plenty of fuel. The temperature theory hadn't entered my mind at that point. Testing that would be a challenge!

Just to re-iterate that the problem at 4000 rpm happened out of the blue, the car has been running perfectly on the previous trip. I hadn't touched anything on the car for months.
I was in the exact same situation following all the work detailed above - i.e. running perfectly for a while before the 4000 rpm problem kicked in.
At this point, I replaced the Hella Ignition modules and now the car is idling at 500rpm and bringing it up to speed causes misfires (running lean?). I'm going to stick a new set of plugs in as the old ones had become fouled and go from there. By the time they turn up I will hopefully have cleared my mind!

 

The advance retard mechanism works using centrifugal force - bob weights and springs. (Marelli SM805A). I have checked this and it was fine, I relubricated it whilst I was there.
The Hella Ignition modules sit between the sensors on the Marelli SM805A and the coils - turning the pulses from the SM805A into triggers for the coils.

I totally agree with your suggestion that it may be stuck in a retarded state. But at the moment I feel that I have exhausted that avenue.
I'm keen to get the car back on the road but I am distracted with installing a new staircase at the moment!