misfire

[glynny]

my morris minor has been running fine and i havent changed anything but mon my last two outings after approx 5-10 mins when i accelerate the engine seems to be misfiring and juddering it is not all the time but intermittent but it seems ok on tick over anybody here any ideas?

[oliver90owner]

Seems to me it needs a good service!

[bmcecosse]

Possibly fuel starvation - throw away any filters that have been fitted - and if that doesn't help -do a flow test on the pump ie pump fuel into a pint vessel and see how long that takes. Other (rather unlikely) possibility is a vacuum forming in the fuel tank after a few miles if the filler cap is not vented. Test here is to stop when the misfiring comes on -and listen for an inrush of air. If all that fails - check points gap and replace the condenser - pref with one from the Distributor Doctor - but just about anything will do in the short term to see if it cures the problem.

[mogbob]

If you not familiar with the vacuum test procedure , I believe Roy meant

" when misfire comes on "

... remove petrol filler cap..."

and listen for an inrush of air."

in his response.
Bob

[bmcecosse]

Indeed!

[oliver90owner]

Do not 'throw away' only. Replace with good ones just as a normal service replacement item, if there is any risk of unwanted solids coming from the tank

I have only experienced condenser failure 2 or 3 times in 40+ years - and one of those was a B&S cultivator engine.

Testing is easy with a mutimeter and simple observations can indicate whether a possible condenser problem exists.

Is the spark a good, sharp, bright blue flash or yellowish at all? Testing direct, from the coil to earth is best - you should get at least a 6mm spark if your ignition system is up to scratch, but there may be other faults if it is less than that.

Are the points being burned severely in double quick time? Particularly if the points gap was correct and metal is being eroded from one contact and deposited on the other. Using a 6 volt coil on a 12 volt system can also destroy points in a short time.

I have well over a dozen magnetos, all but one are over 70 years old, but I've never needed to change a condenser in one of those, yet. Changing a good condenser for a new one may not be a sensible move!

Has the fuel been contaminated? A different supply? Some engines require different timing for fuel used. Modern day fuels do not store as well as previous recipes.

But doesn't seem like anything a good service should not clear up.

[bmcecosse]

The SU fuel pump can't cope with filters - neither are any necessary. The pump itself has a basic filter in the base, but in any case the SU carb is not troubled by any dirt that may get past the pump filter - it doesn't have any tiny jets like lesser carbs. Filters - especially on the pump inlet side - are well known for causing fuel flow problems - especially in hot weather.

[glynny]

took it out for a test drive and was misfiring until i came to a steep hill then cleared up no misfiring for the ten minute journey home then misfire returned after been left for few hours

[liammonty]

Have you actually changed anything yet? It sounds like an ignition problem to me to be honest - they most often are these days as the components aren't as reliable as they once were (or if the car is fitted with 'reliable' old ignition components, they are likely years old). I would give it a good service (as already suggested) then replace ignition components one by one, keeping hold of the old ones in case any of the new are faulty. Condenser, points, HT leads, coil, rotor arm etc. are all potential culprits.

[dalebrignall]

if you change ignition parts get qualiaty stuff from distributer doctor ,accuspark or powerspark

[bmcecosse]

So - it was ok on a steep hill - going UP I assume... Is there enough petrol in the tank ????? Is the pump hammering away nineteen to the dozen when the misfiring occurs? May be something to do with the vacuum advance - which would not be doing anything on the uphill drag - but will pull the timing up on the flat. The movement in the plate may be disturbing the little 'low volts' wire that snakes across the baseplate.

[glynny]

i shall take all your post s into consideration when i get chance to look at the car on sunday and yes it was going uphill at the time with at least half a tank of fuel ill keep you posted

[glynny]

have been tinkering took off fuel pump and cleaned contacts as were rather dirty cleaned filter too which had about a cm of gunge in it, checked carb slide was opening and closing with air filter off and cleaned all the crap out of the distributor cap been out twice for a total of approx 50 mins at all speeds and no misfire so fingers crossed thanks for all your suggestions

[morris van]

One my MG it was the condenser but on my Morris van the choke wasn't going completely off. I fiddled about with the cable at the carburettor end and all is fine.

[glynny]

need to get a service kit then so where would you reccomend dont want to put rubbish parts on

[bmcecosse]

Why do you need a 'service kit'? And for what ?? Diagnose the problem before rushing in with 'service kits'....... Only ever change ONE part at a time, otherwise you can just get in to deeper trouble.

[glynny]

need a sevice kit so dont have to keep mail ordering lots of diferent parts .when i will need them all eventually so ordering one at a time seems to me to be a false economy, and yes am eliminating things one at a time

[glynny]

not the fuel pump bypassed with a seperate tank above the carb still ran the same

[glynny]

just recieved some spares for my distributor and nothing seems to fit i have a 1969 engine fitted anyone no what model distributor it is and where can i get spares for it rotor arm cap etc even the condensor and points are different[frame][/frame][frame][/frame][frame][/frame][frame][/frame][frame][/frame][frame][/frame]

[dalebrignall]

looks like you have the lucas 45 d distributer you need pionts condenser,rotor arm and cap for one of those . the new bits you have are for the 25 d distributer , and get a red rotorif you can as well . the 45 d is a much better unit .