Morris Minor Owners Club

I'm presuming this is electrical as you will see:
67 Traveller. car starts OK and drives OK for anything between 4-5 miles and 10-15 miles. Then I start getting a misfire. It gradually gets worse and worse until the car cuts out completely. I have renewed the points, condenser and rotor arm, and am about to renew the coil, HT leads and distributor cap this afternoon. It appears that when this misfire starts there is fuel in the float chamber so I don't think it's that, plus if I disconnect the fuel line from the carb, put it in a container and turn the ignition on, the pump just sits there pumping out fuel. The only other thing that it could be is that the LT wire from the connector to the points pillar inside the distributor is exposed and seems to be quite thin. But if it's that, it would have an effect from start-up, wouldn't it, rather than as a factor of time/miles/temperature?

Can anyone suggest anything else that it might be, or whether I have missed anything? (It's getting very annoying having to double the travel times purely incase it starts misfiring!)

Thanks

It may well be the coil which is starting to break down as it warms up.

Judge wrote:It may well be the coil which is starting to break down as it warms up.

Yes I'm hoping and praying that when I renew that this afternoon, all will be well!

If not, it's worth changing the rotor arm again... (see parts quality thread!), had exactly this on a Triumph 1300FWD and a NOS rotor arm cured it - intermittent/weak spark when warm.

Phil.

I seem to recall a similar instance with a faulty condenser, but where do you stop

Thanks to all who replied - looks like it was the coil.

Thought so, I think most of us have suffered this problem. Glad your sorted.

I've just spent the last couple of weekends trying to sort out exactly the same problem with my 1971 Travaller. I could have saved myself a lot of time if I'd read this thread! I started on the fuel system and I now know a lot more about SU carbs. I finally tracked the problem down to the condenser that I replaced along with the points as a service item 500 miles ago. Luckily I kept the old condenser and sticking it back on cured the misfire.
Who was it that said 'if it ain't broke, don't fix it'?

I think with the quality of condensers these days the best advice has to be leave well alone.

Keep a spare in the boot but if the one in the distributor is OK, don't replace it.

Condensers and coils - both can fail when hot. Would be interesting to refit that old coil to see if the problem returns - if it does - throw it away.
Mark - : Si fractum non sit, noli id reficere.

I like your signature line, especially after I translated it with an online latin translator:

If you wish to break in pieces not he is , be unwilling this to repair

I've managed to acumalate several faulty coils and when testing them they've all caused radio interfierence (especially using tapes). So this may be a good indicator as to the health of the coil if you have a radio fitted.