Misfire woes

[speedbox]

Hello moggie chums another misfire problem, our 68 traveller is used daily and well serviced but has developed a misfire/fuel shortage at high speeds . I replaced the fuel pump with a new S.U pump thinking that was it, no change.All the leads, points,plugs,condenser,cap ,coil etc are changed every year and were last changed about six months ago.The odd thing is it doesn't do it on the morning run to work (30 miles) only in the afternoon on the way back, when going along at sixty suddenly the car will start to splutter and then if you back off the throttle it will pick up and carry on .The car has no modifications other than a stainless exhaust,brake servo and un-leaded head other than that all standard. Hope some of you knowledgeable types will be able to point me in the right direction, many thanks Darren

[bmcecosse]

Try another coil - they really don't need changing EVERY year - the one you have could be faulty. Could also be vacuum forming in the fuel tank - next time it happens take the filler cap off and listen for an inrush of air.

[kennatt]

strange that it only happens on the way back from work,whats different is back from work an uphill or different route whats the change If the cars stood all day then comming back should be no difference,from going after standing all night.Is going to work a slower drive and back faster.If you can identify the difference then you may be able to spot the problem

[speedbox]

No difference in the way i drive and certainly no hills to speak of up here in Norfolk! It was strange the way it picked up after dying as it would carry on as normal as soon as you back off the throttle for a couple of seconds then put your foot down it would be off again. This is what led me to think the fuel pump was not working correctly and my pump was a nasty looking after market one so i replaced it with a correct SU. No change there so i may try another coil fom my 68 van and see if there is any change. Forgot to mention two other mods i have an alternator and a larger capacity fuel tank , not sure if they would have any effect on my predicament. Many thanks again Darren

[bmcecosse]

Didn't know there was a 'larger capacity' fuel tank available! It my be fuel starvation from debris in the tank - still doesn't explain why only on way home!

[bigginger]

Has been available for a long, long time.
a

[steve4063]

definatley not saying its this but just a little thought for the day

a friend of mine had trouble with his classic after restoring it. he'd had the fuel tank out for a while while doing work and when it was all back together.

occasionly it would run fine and then every now and again it would stop.

they figured it out to occasional fuel starvation but couldn't figure out why.

after weeks and weeks of investigation it turned out there was a leaf in the tank and occasionly it moved towards the output tube blocking the fuel from coming out.

leaf removed no more troubles

makes u think hey

[bmcecosse]

Makes me wonder how he removed the leaf!

[speedbox]

Well thanks for all your thoughts on this matter but it appears to be sorted although i can't explain why. I tried a new coil with no luck, condenser, then looked at the points with nothing out of the ordinary, checked all the leads , plugs etc all ok there so i thought it must be a fuel problem. The only thing i noticed was a lot of that mayonnaise type oil that seems quite prevalent on our cars in the rocker oil filler and even more built up in the breather pipe and on removal of the air filter box an awful lot of condensation in the filter. I'm no mechanic but im guessing that as the engine got hotter the mayonnaise type stuff got thinner and the condensation got into the carb and started the poor running. All sounds a bit far fetched and a bit random but i removed the rocker breather pipe and went for a 30 mile trip without a hint of a misfire and the old girl ran like a dream. Will keep an eye on things and am not quite sure if it's a bad move to disconnect the pipe at the filter end hope it won't do any damage , all quite a relief to get it back to normal and thanks again for all your help what a lifeline this club is, all the best Darren

[bmcecosse]

Ahhh - that's it - the gunge has completely blocked the paper air filter element. It's much better to re-route that breather so it appears inside the air cleaner element - so the fumes etc are drawn straight into the engine - and not onto the paper filter. Your breathers must be well blocked to have all that mayonnaise - engine could also be running too cold - or just used for lots of short runs. Worst possibility is that the cylinder head gasket has blown - leaking water into the oil. I suggest remove and clean the rocker cover and the breather pipes (including the tappet cover breather) - and change the oil and filter - and of course a new air filter is urgently needed. Then take the car for a good hard run at least once a week - and keep an eye on Mayonnaise production rate!

[speedbox]

Good tip i shall give that a go in due course , running like a dream now and i have changed the air filter as it was saturated . I have left the breather disconnected at the air filter end and wil see what happens and then get on with cleaning out all that gunge, all part of the joy of old car ownership! Kind regards Darren