Misfire on Moggy

[johnhannam]

Can anyone help.
My 948cc Morris Minor has had a persistant problem. If I drive it for more than about 20 miles it misfires and then stops. It will restart after a few minutes rest but will then stop again soon.After a good rest it will run for another 20miles. Perhaps I should confine myself to 15 mile journeys?
I have replaced the fuel pump with an electronic one, fitted an electronic ignition, replaced the cyliner head for an unleaded one. I have twice substituted the coil for another one. The dynamo charges well. The engine is in good condition and uses very little petrol or water. The ignition has no condensor and no points. the engine does not overheat and their is no oil or water leak. The carburettor is clean and seems to work well. Their is no sign of overheating.
What have I missed as the car continues to misbehave?
Regards,
John

[katy]

it misfires and then stops

Sounds like an electrical or ignition problem. Possibly a loose connection. Double check the connections on the coil, including the HT one inside the tower. You might try replacing the HT lead between the coil and the distributor. Also check the distributor cap and rotor very carefully.

[Neil MG]

Yes, could be the rotor arm or cap arcing when hot. Or if it could be the electronic ignition! Very common problem with the old Luminition system.

[phurn]

or a pressurised tank. when it dies, try opening your petrol cap. if it hisses then bingo!

[bmcecosse]

Yes - as above - I would suspect a vacuum (not pressure) in the fuel tank - sucking noise as you release the cap. The electronic fuel pumps don't have a good reputation - is it ticking ok when the engine cuts out? When you go for a restart after a wee rest - does the pump tick furiously at first as it fills up the carb bowl ?

[chrisryder]

does the pump tick furiously at first as it fills up the carb bowl ?

out of interest, mine's been doing that recently. what would cause that?

[phurn]

Leaky pipe? Partial blockage perhaps.. carb trouble? When I turn mine on, i get two loud clunks from the fuel pump, then its silent till next time.

[Stig]

Sounds similar to the problem I had recently:
http://www.mmoc.org.uk/viewtopic.php?f=4&t=38208

Drove it into work today and although it needs a bit of a tune-up it showed no sign of conking out with the replacement rotor arm.

[johnhannam]

Thanks for all the advice. I will work through the alternatives and report back.

It's unlikely to be the electronic ignition as the misfire/cutout happens both with my previous points and the electronic ignition that replaced it.
The electronic fuel pump is working well and does not click randomly. Again the problem also occured with the old mechanical pump.
The ignition components are all new but I have followed the debate on new rotor arms so I may refit the older Lucas one.
I will also check to see if the internal pipe in the carb has colapsed.

[rayofleamington]

fuel delivery - the dangerous but quick way to test this is to remove the pipe from the carb when it gets to this condition. You should get a good flow of fuel* as the fuel pump will tick into life!

If you only get a dribble then it's fuel delivery related!

* - maybe best not to smoke, keep the fuel away from the exhaust, don't have any rags underbonnet and have an open 2l coke bottle (filled with water) nearby in case of fire. I've done this many times with no problems (and without any precautions ), but I know that's more by luck than judgment!!

~if the fuel delivery is opk, either the block is in the carb or you aren't gettign a spark - carry a spare working plug and stick it on #1 lead and the plug on top of a bare metal head nut. Obviously check you can see a spark doing this before setting off!! then repaeat when you get the non-running and this will show if the spark has gone. On bright summer days this is much harder so do it at night or try and find shade.

[IanC]

Given the safety (not to mention cost) implications of Ray's advice it might be worth enlisting someone to help you do the old pipe removal test. Get a container small enough to get lower than the carb then place the end of the pipe into the container, whilst your help turns over the ignition. This will fill up pretty quick but would prevent any (or most) of the fuel spilling over the engine and you only need to see this for a second or two to make a judgment on the fuel delivery.

Added benefit - if you get a clean container you can then pour it back into the fuel tank rather than watch it evaporate from the garage/driveway!

[johnhannam]

Hi All ,
Thanks for all the advice. I think I have finally found the problem but only after replacing everything with working spares. The rubber fuel pipe between the pump and carb had a blockage which looked like a small bit of paper in it. This was free to move in the pipe but worked its way with the fuel flow to the carburetor inlet and blocked it as I drove. The engine cut out when the float chamber emptied but after a while the paper fell away from the carb inlet and the pump refilled the float chamber and the car started. i spotted the paper after testing the fuel pump by running fuel into a jam jar. The fuel flow was normal of course but the paper was visible. Thanks for all the help.
Regards,
John

[bmcecosse]

Well done - good detective work.

[MarkyB]

Tricky one, nice job sorting it out!

[mike.perry]

[quote="rayofleamington"]fuel delivery - the dangerous but quick way to test this is to remove the pipe from the carb when it gets to this condition. You should get a good flow of fuel* as the fuel pump will tick into life!

The safest way to carry out this test is to disconnect the wire from the terminal on the end of the pump, turn on the ignition and briefly touch the wire against the terminal. One ore two clicks should tell if the pump is working. You can put the end of the fuel line into a container.