strange misfire
Turbo Mini Forums

Sorry, this is not a turbo related question, but this has me stumbled....

The car in question is a 1975 clubman estate (has HS4 carb and 45D dissy)

It has been parked for a year, but I have now gotten it through a MOT and its on the road, the only problem is this misfire.

It can do it both when cold and hot, but it typically starts when the revs are not too high (no rev counter). When it starts it will go on with higher or lower revs, and if let down to idle it can make the car stop. it can be just slight hesitations, or larger troubles where it really rocks the engine mounts, and it seems like there is more than one cylinder falling out.

It continues to do this for a while before eventually recovering and continues to work fine a for a while (up to 20 minutes maybe).

The plug leads, coil lead, rotor, cap, condenser and points are fairly new (looks brand new, possibly a bit more than a year old, very little use).

I have reset the points to a 0.35 mm gap.

I have tried another secondhand coil.

I have blown through the carb yet (from the yet towards the float), but could not empty the float afterwards as carb was still attached to car.

I have installed a new fuel filter.

I have reset the points once again.

I have fiddled slightly with the mixture, nothing changed with the misfires.

I have checked the low voltage leads to/from the coil, they are all good (no resistance)

I have measured the voltage to the coil, while rocking the ignition key (if the ignition switch was the problem), but no change in voltage.

The starter motor turns freely when it does this (if stopped and tested) so I do not think its the engine ground.

It has got 1/3 tank with 1 year old petrol, the rest is new (currently full), there was no difference after filling it up with the new petrol, it did the same both before and after doing that.


Any ideas? I am out of possible causes, and I am supposed to drive this car 300 miles on Sunday....

Any suggestions appreciated!

Dash pot oil?
rockers adjsted?
vac advance pipe?
vac leak at carb?
leaky float?
dodgy mech fuel pump?
LT wires breaking down?

MM points. There has been loads of problems recently with the quality of points. Bin them and fit electronic

There are also a lot of crap condensers about these days.

When Sturgeo was running his daily, the only condenser that I could find that would run the engine was from an old dizzy in the parts bin.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

vac pipe to dizzy, carb vac leak engine running lean
breather pipe to carb leaking, split
coil breaking down intermittent fault,
cracked dizzy cap, condenser fault this will be evident by the points tinged blue.

there is oil in the dashpot, breather pipe connection on carb is blocked, I have tried 3 coils, dizzy cap is good, points look good (not blue).

float does not leak and I have looked in the float when it has happened, there is fuel there.

HT leads are new.

I have bypassed the + wire to the coil (put it to constant battery + and disconnected the other) and it still happened.

VAC leaks from dizzy pipe would not give this sort of problems would it? and its also good, I just went outside to have a look.

Plugs are new BP5ES's (std 998 engine)

Try a new condensor would be my bet

dont rule out a goosed head gasket.

do a CR check usually between 2 and 3 bore its blown

How old is the dizzzy, might there be some wear in the bearing? This would give sloppy spark distribution/scatter!

sorry, never updated this.

Tried to change for new points, no change, tried 3 condensors, no change. Swapped the complete dissy. Voila, everything good, and have been since. It is now sporting a 23D dizzy from an 63 850, with what looks like original points and condensor :)

conclusion:- the dizzy was goosed giving excentric spark

job done

ah ha, that cheered me rightup. im not a dizzy after all