Misfiring, spark and carburettors... Distributor repair SORTED!

I think that having adjusted the acceleration pump and float height  I have just about cured the  flooding issue. However I do still have a problem in that the car is running extremely roughly and the motor shakes about. On a second point I had  already noted that on occasion and for no apparent reason all ignition would cease and I lost all sparks! This  problem vanished and reappeared after I had fiddled with the AB14/distributor lead. This may have been significant (indicating lead failure) or a coincidence. I suspect therefore that at the moment I have two problems- which may or may not be related. These issues are very vexing as I have spent a long time trying to get this car recommissioned and yet there seems to be one problem after another. I took this car on as it seems to me that it was crying out for rescue from its LBPO; but if anything perhaps its one motor that just didn't want to be saved!

Rough running:
Thinking back, although I don't recall touching anything that caused the problem, this rough running problem had started before I had begun messing with the carbs at all- about the time I adjusted the timing in fact. Prior to this it had been running well and I had been able to reach operating temperature. This means that the timing and the possible problem with the AB14 lead have to be my starting points. However, resetting the timing to 10 deg btdc static had no discernible effect so I don't think my timing adjustment can be to blame. It was clear however that advancing the timing through 20 deg btdc did lead to a rapid pickup in motor speed but sadly no smoother running. 

I found that I could remove the plug leads on cylinders 1 and 2 with no effect, whereas removing those from 3 or 4 led to an immediate stall. The conclusion from this is that the motor is simply not firing on cylinders 1 and 2, and only roughly on 3 and 4. Firing requires fuel, air and a spark at the right time. I also have a set of the red Sealey spark-plug top spark indicators, and fitting these showed sparking was even and regular on all 4 cylinders; I still haven't changed the AB14 lead but this is obviously working at this time since I'm getting sparks. Of course it is still possible that the sparking plugs in  cylinders 1 and 2 had failed meaning that discharge wasn't resulting an a spark in the cylinder. I changed these two for new plugs... but to no effect.

Since spark and timing appear correct (or at least as correct as they were before this problem appeared), this must indicate a carburation problem- and cylinders 1 and 2 are of course served by the same carburettor. Advancing the timing did seem to improve matters, and given the spitting above, I think these could both indicate a weakness in the mixture (too little fuel or too much air). I removed the anti-tamper plugs and adjusted the idle mixture screws- this also failed to improve matters and they seemed set in just about the optimum positions on cylinders 3 and 4 anyway. Adjusting them had no effect in the non-firing 1 and 2. 

Fuel starvation is an obvious cause of weak mixture and this could suggest blocked jet(s) somewhere. After all I did find some sediment in the front carb when I swapped the carb tops, and so maybe I'm still flushing dirt through the system? I removed all jets and checked that all were open and all passages in both carbs passed carb spray easily. This time I managed to separate the jets from the idle jet holders as I needed to make sure these were clean. They were tight and I'd lacked the confidence to pull hard last time-Nowadays I'm much more blase about these things and I just pushed them out using a screwdriver blade lodged in the gap between holder and jet and pushing.

Idle jets separated from holder

Now I was able to give them all a good clean inside the holder and check that the jets were clear- they were! I even removed and cleaned through the idle mixture jets as well (these hadn't been touched before) and reset them to their original positions. There was no detectable blockage anywhere.  

I tried squirting "Dampstart" into carburettor barrels 1 and 2 and this did lead to firing in these two cylinders and a slight smoothing of the idle; although it was still very rough. Once more this suggests lack of fuel or a mixture problem.

Excess air in the mixture might arise if I had failed to get the carburettor spacer "O" rings back correctly. These are difficult to fit properly since they seem to be too big for the grooves into which they are supposed to fit and grow even longer in use. Should one or more be trapped overlapping its groove then this would create an air leak and also lead to weakness. Anyway- seeing no alternative, I removed the carbs again and checked that the spacer "O" rings were correctly positioned (they were) and that the spacers (anti-reversion) were installed the correct way around (conical side pointing towards the motor)- again!  I refitted the carbs fitting a new "O" ring for one that was now too long to fit back into its groove... and now Hey-presto... NO difference at all!

I now started to worry in case something was seriously amiss with these two cylinders- eg blown through head gasket. I therefore carried out the long awaited compression test. To my delight the news was GOOD... I obtained values of (1 to 4) 175, 170, 172, 175 psi which is well within tolerances. At least this enabled me to exclude the possibility of gas leakage or a sticking valve.

Lack of Spark
At this point I began to despair of ever getting this motor to run again and wondered if I had simply imagined that it had ever run nicely? I rechecked my blog to jog my memory- and I hadn't! Although I don't know what can have happened to cause this symptom. However, thus far I have only set the timing at idle speed using the static value of 10 deg btdc. Dynamic timing setting is usually done at full advance and in fact this car doesn't have a specification for dynamic timing at idle; only a static setting of 10 degrees and a dynamic setting (fully advanced) of  25 deg btdc at 3,000 rpm. I tried to run up the motor to achieve this rpm and set the timing at this value in case it improved matters- or at least I was attempting to do this... when the motor died completely and would not restart! The cause was quickly identified as a return of my previous no-spark problem. However this time it appeared to be permanent and moving the Ab14 lead had no effect. 

At least "permanence" should make identification of the cause possible, and fortunately its not too long since I had to try and fix a lack of a spark previously! I was able to show fairly quickly that there was no spark at the cylinders; and although there was a good 12V supply at the coil, there was no switching via the ignition module- when tested with an LED no earthing was evident at all. I also checked the switching signal current emerging from the distributor at cranking speed (it will increase with rpm) and detected an output of 0.015V AC which is at least 1/10th of that I had observed previously and probably not enough to trigger the module. I had tested for this voltage at the end of the lead, just disconnecting it from the AB14. As, the lead was itself suspect I then disconnected the 2 pin WM12 connector and tested again at that point. The output was unchanged so at this time it suggested the distributor might be faulty. I tested the module anyway using the YWB135 and it passed. 

Inside the AB14- all looks quite clean

YXB135 in use- having connected the module correct functioning is indicated by a flashing amber light- this was present so modules passed!

I removed the distributor in order to test it further. Spinning the shaft by hand (give it a good flick-spin between finger and thumb) and testing for output could generate values of 0.3V AC but this was highly variable. Some spins led to no detectable output at all! Presence or absence of output didn't correlate with any particular reluctor teeth. 

The pickup coil used here is the Lucas DPB104. I checked pickup resistance and found that it was either Infinite or the expected value of 3.5 Kohm! 

Open circuit across pickup coil from internal lead WM12 connector.

This suggested to me that the distributor is probably OK, but that there could be an intermittent break in the leads- the AB14 lead was already suspect. I suspected the connection to the 2 pin plug on the distributor side. The silicone wires flex here where they enter the rigid terminal and its a likely break point. I cut the plugs off both distributor and AB14 leads and retested. I was still getting poor (if any) AC voltage induction and the resistance of the pickup kept defaulting to open circuit- the break must be further down. The next likely point is where the silicone wires enter the distributor. Again this is a fixed point where the wires can flex and potentially break.  I looks like this section too will need to be replaced. 

The problem here is that the wire is silicone covered, I think so that it can move as the timing plate moves in the distributor in response to the centrifugal advance and retard mechanism without building up spring pressure. I don't have any more silicone wire of the correct gauge, but the wire on my spare WM12s is quite fine and I'm hoping will be flexible enough.

Inside the distributor once the rotor arm, flash-shield and wire guide have been removed. Black silicone leads visible connecting to pickup coil.

 I cut the wires and then used a Dremmel to carefully slice through the lower half of the blue distributor side plug.

Cutting through the blue distributor body grommet plug

 This allowed me to lever out the old wires and...

 ...replace them with those on the WM12 terminal.

I slipped some heat-shrink tubing on and then twisted the new wire to the old and secured with solder. The output from the distributor is AC so I don't think that the polarity of connection is an issue....however the connection to the ignition module is "handed" with colour coded wires and unequal connection sizes. I therefore tried to maintain the connection sense although this isn't helped by the fact that both pick up silicone wires are black!

Soldered join- silicone pickup wire to WM12 terminal

 Slip up the heat shrink and

 Shrink it into position. I included a generous loop of wire so that any movement of the base plate could be accommodated.

Wire joins covered and placed in wire guide, blue grommet plug back in distributor body (slit is at the bottom)

I could now get a consistent reading for resistance of the pickup coil and hand-spun AC output around 0.2-0.3V. I refitted the distributor and reset the static timing. This time the motor fired!! Once more I had sparks on all cylinders, but equally, cylinders 1 and 2 were still not firing and the motor still sounded really rough. 

In truth I hadn't expected the spark problem to have been the cause of the misfire (didn't fit the observation). I rechecked all fuel levels; they are still low although I dont know why as floats are all set correctly; but they are roughly the same in each carb at around 30mm. I swapped the carb heads again with no effect. I rechecked float height and droop and both settings are still correct in both carbs. I even fitted a new float and readjusted that to the same settings- with the same resulting fuel level. I suspect therefore that the apparently low fuel level may simply be the result of measuring it on a sloping drive! In any event I can discount it as the cause of my problems  because... if its high enough for cylinders 3 and 4 to fire, then it should be high enough for cylinders 1 and 2!! I will address it again if and when the car is mobile and can be driven somewhere flatter!

Solution!!! At this point I appeared to have eliminated everything! However, recalling the "Dampstart" effect described above I decided to see if cylinders 1 and 2 could actually fire at all so I disconnected 3 and 4 sparking plugs to avoid confusion, and started the motor. To my surprise it ran but roughly and needed much larger throttle openings, it wouldn't idle at all if the throttle was released.

This was a very satisfactory finding and led me to the real problem- which has probably been apparent to those more experienced than I ever since I started describing it - and that is that although the motor and carbs have just been rebuilt; the carbs have never been balanced! Although I will do this properly later, for the moment I was able to open the throttle of carb (1) relative to that on carb (2) to get all 4 cylinders to run. Provided the throttle on the rear carb (2) is braced on the idle screw then screwing in the carburettor balance adjuster will open the throttle on the front carb relative to that on the rear. This allowed both front cylinders to fire resulting in an increase in engine speed. I could then back off the idle speed screw and repeat the process until the motor started running poorly again. I could then back off the carb balance adjuster and finally set the idle speed to a more sensible value. Eventually, I obtained a smooth running (but still unbalanced) motor that should let me set these parameters more systematically.

Luckily I have a Supastrobe bought many moons ago and this allows you to dial in the amount of advance required and then re-strobe at TDC. I could then set 25 deg on the strobe and run the motor up to 3000 rpm.

However- a word of warning... obviously if you are about to adjust the timing then the distributor clip needs to be loose. I guess I am more used to vertically mounted distributors where the weight of the unit will hold it into the block...sadly this one is not only horizontally positioned, its also spring mounted and as I revved the motor at 3000 the vibrating eventually threw it out of the driving dog- nasty noises and motor stopped completely! This was a worrying time but once I'd worked out what had happened it wasn't too bad. However the shock of being shot unwillingly from the very final stage in the adjustment to right back to the start and having to reset static timing reluctor position was very disheartening! Remember to keep hold of the distributor and exert some inward pressure to keep it in its mounting. I did get the thing timed- although I suspect its not running as well as it was before my mishap but hopefully this will be cured by proper carburettor balancing- which has to be my next step!