Mk2 fails to proceed

[lordphi]

Early last Friday evening my Mk2 (1963 3.4 manual overdrive) stopped itself on the way home from the local pub.

Precursors (that may or may not be relevant)
Since buying the car late last year I have driven maybe 200 miles without trouble, but not as crisply I I believe it should. Never-the-less it started on the button every time.
Last week I changed the ignition system to a new distributor with electronic ignition, new plug leads and new spark plugs. I also replaced the dud dynamo with a new alternator and dummy control box.
The car ran well for about 50 miles. This was a mixture of journeys so the car demonstrated both cold and hot running.

The Event
The car ran well for the first 500 yards from the pub (thus the chock was probably still operating). Without warning it cut out – dead! Attempts to restart produced no results, so we pushed it back to the pub car park. Further attempts to restart resulted in a few backfires, through the carburettor inlet side. The AA was called but could not identify the cause, so then they relay trailered us home. The AA confirmed that there was a good spark, that fuel was plentiful at the under bonnet fuel filter and that the choke solenoid was functioning.

Since then
Checked the ignition timing (with a strobe light, whilst the engine was turned over by the starter motor), proving that there is a spark and that it is sparking at the correct time.
I removed carburettors and gave a thorough clean and inspected for faults – none found.

Then I thought I had found the fault. There are two rubber pipes (behind and under the SU carburettors) connecting the feed from the choke carburettor to the inlet manifold. They were perished and cracked through (maybe they don’t last much more than 50 years).

I reassembled everything, set the slow running and mixture strength according to the handbook and tried starting the car. No improvement, only the occasional backfire, again through the inlet system.

In case I have reassembled something incorrectly I stripped the carbs down again, reassembled them and tried starting again. No joy. I have now exhausted my knowledge/skills and as for any help or advice someone out there can offer.

Thanks

Phil

[oldtimer]

Hi Phil,
Very interesting, I have read through a couple of times trying to get the measure of the problem.

Firstly , you say that, Quote, The choke was probably still operating. Most people used to install a switch to cut the choke off. - as I did. This electric choke was used across several models of the day and were effective in starting the engine but it was rare to be able to leave the engine running on choke even to close the garage door because it would choke it's self to death by gross over fuelling. Trying to restart the engine then became a mammoth task. This is probably a bye the bye in relation to your specific problem but worth bearing in mind.

Having gone through the routine you have described where to next ?

With a bang through the carb there is clearly some fuel and a spark but not at the correct time.

As it is not an onerous task I think I might carry out a compression check, just to satisfy myself that every thing is in order in respect to valves opening and closing correctly.

This now brings us back to the distributor. Firstly, check the distributor cap and rotor arm for tracking - I guess you are familiar what to look for. If you have a spare rotor arm and cap try substituting them.

And finally, you say that you had completed about two hundred miles prior to fitting the new distributor. If the problem is not identified with the above I would suggest you refit the old distributor in order to isolate the malfunction

I hope that helps a bit and good luck but do let us know your progress

Oldtimer

PS Is there any danger of water in the fuel tank - they don't like running on that stuff !!!!

[Martec]

Hi Phil,

A number of things come to mine from your writing,

You say you changed from a dynamo (positive earth) to an Alternator (negative earth) did you change the other items over as well (I would need to think what else needs changing but it is catalogued on here).

As you have found two rotten pipes are there any others, I'm thinking of the vacuum take off at the back of the manifold and the rubber connector below the manifold.

I believe that a back fire through the carbs is a weak mixture or miss timed ignition, worth checking fuel filters that are fitted.

The new distributor, is it worth as Oldtimer says refitting the old dizzy as the rotor arm is often a problem.

It would be interesting to know what plugs and dizzzy you have you have in.

Best of luck
Brian

[piman]

Hello Brian,

well spotted, certainly the coil polarity should be changed as the spark will be weaker without doing so. On mine the fuel pump is polarity conscious as the spark suppression is a diode across the points but as there is fuel that would not seem likely in this case?

I came across a similar thing on another forum and although there was a spark at the plugs when checked out of the engine, it was too weak when the plugs are installed, poor conection within the distributor was the fault.

I think a thorough check of all fuel and ignition systems is called for as it ran for a while even if the coil is cross connected.

Alec

[lordphi]

Thanks for your thoughtful replies.

I'm sure there is some sort of Sherlock Homes type law that says 'the most obvious is the most likely'. With the addition of new points and HT leads I returned to the original distributor set up. Immediate success. She runs like a dream again.

The new electronic ignition distributor will be going back to the supplier for a refund. I can't say that Accuspark is generically a bad product, but I can no longer trust it as a solution for my Mk2.

I must try to find someone who can explain 'electronics' to me. My experience is that electronic gadgets simply work or do not work. In the case of this electronic distributor it produced sparks and at the correct timing external to the combustion chambers, but inexplicably it did not ignite fuel in the combustion chambers....weird!

Phil

[Decopab]

Hi Phil,

I've had a similar experience recently with a powerspark ignition unit. It worked fine for a few months but then started giving issues. I Wasted far too much time messing about trying to trace the problem and even got the unit replaced with no success. Eventually I replaced the points and of course it ran perfectly on the first try.
It's a shame because electronic ignition should be a much more efficient way of doing the job, but I'm led to believe that a lot of the cheaper kits are made in China to very low standards and often don't work as intended. Phil

[oldtimer]

Phil,
I'm pleased you have sorted that one, well done.
Don't forget what I said about the electric choke

Oldtimer

[piman]

Hello Decopab,

"It's a shame because electronic ignition should be a much more efficient way of doing the job"

Why do you think that, it may gain slightly in the reduced maintenance but as a much superior way of firing the coil, I very much doubt it in normal circumstances?

Alec

[Decopab]

Oh dear, Ive put my foot in it now! It's just my perception based on fairly limited understanding admittedly. Lower maintence, no mechanical parts to wear out, no condenser to fail, no contacts to rely on for spark effectiveness, allegedly better mpg. My experience with the systems in four cylinder cars has been very favourable too, but here I am running points in the Daimler so what do I know! Still, modern cars run electronic ignition, so there must be something in that.

[peterdpps]

Hi all,
My experience of all things electrical and mechanical is that Murphy has a great deal of input!
The rule of 'if it ain't broke don't mend it' seems often to apply as well.
My 240 is still on conventional dizzy and points and despite lots of reports exalting the advantages of electronics this is one area I have resisted upgrading! However, I also read that some replacement points,condenser and rotor arm can be suspect having probably been sourced from China.

Glad you've got sorted and hope you have lots of fun now your cat is running as it should.

Pete

[PPV]

Phil, just before you send the electronic system back check all coonections especially if not soldered and all earths. I recently had a similar issue (It is on the BB) and mine was on a Powerspark ignition system). It had been running fine then one day just would not start. It coughed and spluttered so I checked the plugs and coil and saw big fat sparks. Timing had not moved so I thought it was carbs/fuel and did all the requisite checks but no joy.
Then by chance just before I changed back to points I looked at the distributor and saw that the earth strap inside moved slightly. I tightened down the earth screw, trid the car and it fired staright away! It happened again a few days later and I thought the same had happened but no it had not, however, checking the wiring to the distributor I found that when I twiddled the wires and tried the car it would start. More investigation and I found that one of the spade type connectors I could pull the wire out of! It had just been crimped in by the supplier but not caught well enough.
I soldered it together, tried the car and it has run fine ever since.
Worth a try.
Best of luck,
Paul

[piman]

Hello Decopab,

my feelings are that a good distributor does not gain any discernible gain from electronic devices to fire the coil. Due to the age of our cars the distributor is likely to be worn out and will benefit from being overhauled and returned to the correct advance curve.

There seem to be many reports of conversion to electronic devices that give appreciable gains but I believe that the change is from a poorly set up distributor and that the modification does nothing to correct weak springs or in extreme situations where the weights have seized up.

Modern cars use electronic ignition but controlled by a computer which also controls the fuelling.
There are systems that can be fitted to older cars which eliminate the distributor but do need some extensive rolling road time and to me are an anachronism.

Alec