'A' Series engine problem - help !

[catdog47]

Hi, just wondered if we have any A'series engine experts around. My Sprite has developed an annoying habit of refusing to start again if it is stalled when hot. I've found that it will start immediately with a little push, but not on the key (?). It always starts well from cold and runs well too.
(It's a 1275 that has been enhanced a little with K&N's big head valve head etc some years ago) I'd be really grateful for any ideas ???

[crankedup]

I'm no expert but suggest it could be fuel vapourisation in the fuel line under the bonnet.

Have you driven the car previously in very hot weather conditions with no problems?

[GreenV8S]

Does it crank over but not fire?
Might be the ignition system not quite producing enough oomph (stop me if I get too technical here) while the starter motor is pulling the battery voltage down. Just as a sanity check you could monitor the battery voltage while trying to start th hot engine, and see if it starts happily if you connect a booster battery using jump leads.

[Mutant Rat]

Are you running a ballasted coil? If so, it sounds like it could be a problem with the 12V 'starting' circuit:

https://www.burtonpower.com/technical/tt_ign.html

[catdog47]

Thanks for all the suggestions - I appreciate it.

I had considered fuel vaporisation, but I couldn't think why it would start with a push if that was the case (?) It was originally tuned with 4-star, but I'm now running with unleaded with redex booster (not sure if thats relevant).

It does crank over (pretty fast) but won't fire. The fact that it starts instantly with a push makes me wonder if it is electrical, but the starter motor was rebuilt (by an auto electrician) so it should be A1.

Not sure about the ballasted coil - but I'll dig my meter out tomorrow and check (the cars a '71). I have suspected the coil - someone had suggested they can sometimes struggle when hot.

Thanks again - all advice gratefully received.

[Mutant Rat]

catdog47 said:

I had considered fuel vaporisation, but I couldn't think why it would start with a push if that was the case (?)

Yep, I was thinking the same thing.

catdog47 said:

It does crank over (pretty fast) but won't fire. The fact that it starts instantly with a push makes me wonder if it is electrical, but the starter motor was rebuilt (by an auto electrician) so it should be A1. Not sure about the ballasted coil - but I'll dig my meter out tomorrow and check (the cars a '71). I have suspected the coil - someone had suggested they can sometimes struggle when hot.

Obviously cranking speed and ignition are not interdependent, but at least the decent cranking rules out battery problems and engine earthing problems.

If it is an inertia starter motor with a separate solenoid & ballast resistor, then there are efectively two low tension ignition feeds to the coil:
1) When the ignition switch is in the 'on' position, there is a feed via the ballast resistor, which reduces voltage at the coil to around 9 volts.

2) When the ignition switch is in the 'cranking' (start) position, there is a feed from a terminal on the solenoid to the coil (which bypasses the ballast resistor & gives a full 12 volts giving the coil an extra 'kick' for starting).

It is the circuit which provides the 12V supply on (2) that I'd suspect.

Could be a duff coil, but more likely a dodgy solenoid or wiring/connection from the terminal on the starter solenoid which is 'live' when cranking.

Edited to add: I ought to stress that I'm making assumptions based on 'normal' wiring layouts for old cars with inertia starter motors and ballasted coils! I've never had the priviledge of owning a Midget, so I'm not familiar with them and could be talking complete bollox!

>> Edited by Mutant Rat on Thursday 30th June 21:40

[Pigeon]

I'm having trouble fitting "1971 A-series" and "ballasted coil" together. I'm pretty sure it's just a straight 12V feed to the coil.

I concur with the view that it's most likely ignition related... check that all the connections are clean and tight, including the fusebox... check the coil as others have said, but also check the condenser and the condition of the points themselves.

[ledger]

I had a similar problem with my 1972 Mini. It turned out to be a dodgy coil. The engine used to actually stall and then not start for a minute or so (I suspect until the coil had cooled).

[Coco H]

I had a vaporisation problem with an A series when it was a very hot day and the car was hillclimbing. The dran thing wouldn't restart at the end of the runs. That is soluble.

[ARH]

If it has an electric pump by the rear axle it will not be fuel vapourisation. that will only happen with a mechanical pump. I would check that when cranking you have a spark as the ingnition switch could be playing up. If so it should start. If standard ignition it should not be ballasted. Could be the condenser overheating, or the coil, but It would do it when driving as well.

[Pigeon]

The electric fuel pump eliminates problems with fuel vaporisation in the pipes but not necessarily in the carbs. If they're feeling too much heat from the exhaust you can get fuel vapour rising out of the jets and collecting in the intake tract with the result that when you first try and start it when it's still hot the mixture is far too rich and it won't go until it's been turned over enough to clear it. However, since it goes instantly with a push this is probably not the problem.

An ignition component on the edge of failure due to heat would not necessarily show up when driving if it wasn't that far gone. When the battery voltage is being pulled down by the starter it weakens the spark and any deficiencies in the system become more obvious.

[catdog47]

Update: After considering all the comments above (many thanks), I decide to fit a new coil. Ordered it, received it, fitted it - same problem (Grrrr !)

Incidentally it is a standard 12v feed. When it stopped (and didn't start with a few turns) I took a plug lead off to check for spark. Not only did it spark, it started up on 3 cylinders !

My neighbour has suggested a condenser (comments ?) but I'm so fed-up I'm close to callng in the hometune man and throwing cash at the problem.

Anyway, asuuming I get the answer eventually I'll let you all know. Thanks again for all the advice.

[Pigeon]

catdog47 said:

Update: After considering all the comments above (many thanks), I decide to fit a new coil. Ordered it, received it, fitted it - same problem (Grrrr !) Incidentally it is a standard 12v feed. When it stopped (and didn't start with a few turns) I took a plug lead off to check for spark. Not only did it spark, it started up on 3 cylinders !

...it started first pot over, or nearly so?

catdog47 said:

My neighbour has suggested a condenser (comments ?) but I'm so fed-up I'm close to callng in the hometune man and throwing cash at the problem.

Pigeon said:

check the condenser

ARH said:

Could be the condenser overheating

Condensers are cheap...

[catdog47]

OK, you persuaded me (I was just a bit P'd off that the coil didn't fix it!) Off to the local spares shop I go...

[LuS1fer]

It never harms to replace all the ignition bits. I would have said the coil too. I had an A40 and had a similar problem traced to the wire between the ignition and the coil. A wiring diagram works wonders. I also assume you've checked for leaks on the vacuum pipe.

[catdog47]

Finally solved it - the problem appears to have been a poor electrical connection to the distributor plate, along with less than perfect points (I did try a new condensor first - no effect). OK I admit it, when the condensor didn't fix it I got the hometune man in (I ran out of both time and patience), but for £40 I was just happy to get it sorted. I still don't understand why it started cold but not hot..

Anyway., big thanks to everyone who offered help and advice - much appreciated.