rough running

[MarkRado]

I have got one of the last Series 2 FHC in my workshop with less than 30.000 miles on the clock, wonderful but with a lot of (smaller) things not working and to be repaired. Its a Swedish car with full US spec.
On my way to the a/c shop for fresh refrigerant, the engine suddenly lost power and behaved as on a cold morning (which it was) without choke. I pulled the choke which helped a little for the moment.
So far I have completely rebuilt and adjusted the Strombergs (new adjustable jets), changed and set plugs plugcaps leads dist cap contact condenser coil incl timing. Temporarily plugged all vac ports. Things improved but still far from sweet running.
Irritating points:
there is not much play in the distributor shaft, nevertheless the timing tool shows dwell jumping all over the place
On the carburation side I came down from the (pre power loss, pre adjustable) jet height of 3,2mm to 2,5mm (below bridge). But both carbs are drawing a lot and almost double the air now (maybe a different story caused by the new jets)

I hesitate to start with the valves which might show the problem because its beyond the initial scope.
I would be grateful for your ideas,
thank you

Mark

[Jack the lad]

Hi Mark, a few things to try, firstly the cam dwell should not be varying about, could be the points need some lubrication on the pivot pin. New points needed if they have not already been fitted. Could be a fuel supply problem, check the supply to the carbs, you are looking for a strong, reliable flow of new clean petrol. If its contaminated it's probably come from the tank (rust) and will now be in your carbs (sorry). Examine the bulkhead fuel filter and replace if not perfect, don't forget the one in the bottom of the tank If you have an MOT test garage near you they should have an exhaust gas analyser which will be useful to see what the mixture strength is, indicating a fuel delivery problem or not. If you can locate a garage in your area with an engine tuning digital oscilloscope, such as the Snap-on "Councillor" they will find the fault in 2 minutes. good luck with it, best regards, John.

[MarkRado]

Thank you John,

good point, fuel is clean in the float chambers (undid it several times) but will clean filter and check pressure.
Ive got a friend who has all the equipment, but I want to rule out the obvious before.

Thank you very much for your input
Mark

[40GT]

Couple of things come to mind.
Firstly I would be looking at the dwell mechanics, is the base plate loose, is the connection to the adv unit good, free but mildly stiff? when operating the vacuum.
Next would be electrical, loss to earth etc, another problem that can happen if the rotor arm passes ( or fires short of ) the cap electrode, is it physically at the correct position to make a clean jump.

I presume you've checked the carb diaphragms for even the smallest hole.

Sean

[JerryL770]

I can't see mention (in your OP) of the distributor rotor arm. Have you checked/replaced that?

[mgcjag]

If the rough running improved by pulling the choke out then that's pointing to fuel issues.....Steve..

[MarkRado]

Thank you all for the moment!

Yes, rotor is new, I will check fuel side and report back.

Mark

[MarkRado]

Problem solved!

I drained the tank and cleaned the fuel filter (everything ok), partially dismantled and checked the distributor once again, ckecked the fuel pressure (SU pump - too high at 4,5psi!?).
Out came the oscilloscope, it showed problems with igniting the mixture - much too lean! I adjusted both jets to 4,6mm below the bridge (needles flush in the piston) and it runs perfectly with Lambda 0,89 an CO 4,2 (this could be a little less).
But lesson learned that the Strombergs need quite a different setting compared to the SUs (ca 1,6mm below bridge on a 4.2).
I wonder how the the Stromberg engines ran when new with a fixed jet height of lets say 3mm (where my problems started)?

Regards
Mark