Misfiring Morris

[crankedup]

Every week I seem to find another ailment to be put right

This week it is a misfire, on start up, which is instant on the button, the engine only runs on 2/3 pots until its warm when it chimes in on the 4 pots. Then just as you feel all is well it will start misfiring again when the engine is hot. I have found that by easing off the throttle for a short while and gently coaxing it will chime back onto 4 pots and run fine for a number of miles, then repeats the same process!!

I have replaced and correctly gapped the plugs, replaced the plug leads. The electronic ignition system is all new and at this point I am a bit puzzeled. I asked the same question on General Gassing forum but am still puzzelled.

Apart from the new ignition system failing (jeez please not that)could it be the fuel flow a problem? The car is fitted with a SU HV2 carb, the suction chamber appeared very low on oil and my Bro' filled it up to just under the oil pot lid thread saying keep it topped up. However I have since heard that this is not so and it should only be a light oiling to the piston rod?? If this is correct I wonder if the suction chamber full of oil may be the cause of the misfire?? or perhaps a partial blockage in jet?? or indeed any suggestions please.

I have come to understand that the reality is that I am carring out a light recommishing to the Morris after its years of apparent inactivity. Steep learnuing curve but well worth it.

[Pigeon]

Your brother was right about the dashpot oil level. The oil isn't (primarily) there for its lubrication properties, it's there for its viscosity, which enables the damper piston to provide resistance to raising of the carb piston. It should be kept topped up to just below the top of the hollow rod that the damper piston fits down inside. If you only "lightly oil the piston rod" the damper won't work and you'll get hesitation and misfiring when you open the throttle due to the lack of acceleration enrichment.

WRT the ignition I've reread your original post and looked up "Magnatronic" on Lumenition's website. It seems to be simply a magnetic-sensor replacement for the points. If that's all you've got - no CDI unit - then the points gap should remain at the original setting of 25 thou, not 40.

[incorrigible]

Try a different coil, and standard plug gaps. Some electronic ignition systems have a habit of loading the coil quite heavily

[crankedup]

incorrigible said:

Try a different coil, and standard plug gaps. Some electronic ignition systems have a habit of loading the coil quite heavily

The car spluttered onto just 2/3 pots today and I only just managed to coax it home. I've booked it into the local garage (they are superb independant)for them to diagnose. They sorted the timing for me following the ignition changes so are familier with the system. The coil was replaced with a 'correct'type by the people who did the ignition work, if its found to be faulty at least I have a two year warrenty. The plugs are as previously used just the gaps widened out to 40-45 thou as recommended.

I will try a spare coil tomorrow before it go'es to garage tho.

Thanks for comments and suggestions.

[M3 Mitch]

Offhand I'd suspect a bad plug, plug wire, or distributor cap, these being easy and cheap to check/replace.

Possibly a vacuum leak that just affects a certain cylinder (BTW is it always the same cylinder that does not fire consistenly? - easy to check, start the motor and run a few seconds, you will have one plug noticably cooler than the others)

Once these are checked, perhaps a sticky valve, or, more ominously, bad head gasket or worse?

[crankedup]

Well the old girl is in the hospital now and hopefully will benefit from the laying on of skilled and sensitive hands. She really is in a bad way with lots of popping back thru the carb, backfiring and misfiring

I shall post up as soon as the diagnosis and repairs are made. Pray that this may not be a wallet busting occasion.

Many thanks for all suggested solutions, sadly to no avail this time, altho I have a feeling it could be valve trouble.

[ARH]

Back fireing and stuff sounds like the timing has slipped. It could be as simple as tracking in the dizzy cap, or even the condenser if it still has one.

Have you checked the compression? Hope it isn't a burnt valve.

[crankedup]

ARH said:

Back fireing and stuff sounds like the timing has slipped. It could be as simple as tracking in the dizzy cap, or even the condenser if it still has one.

Have you checked the compression? Hope it isn't a burnt valve.

The condensor went along with the points when the ignition module was fitted. The car certainly still started up with ease even tho it was only only 2/3 pots, simply touched the starter button and it sprung into life immeadiately everytime. Still waiting for the garage to give me a call with 'car ready' or 'do you still want us to fix it?' They said they would fit it in with thier other work so not at this point overly concerned about time taken.

This could be the end of the road for me and my Morris, may sell her once all the issues are dealt with.

[crankedup]

Morris all sorted now : turned out to be several factors :

1. Plug gaps to wide
2. Carbon frass build up laying in the base of the dizzy, the new carbon button had worn in rather quickly causing the sudden build up.
3. The main culprit was 'end float' in the mag causing fluctuating gap.

So all fixed now and many thanks for all the suggestions to find a way forward.

compression test showed all pots fine and equal. phew.

Edited by crankedup on Tuesday 26th September 19:42